-
Notifications
You must be signed in to change notification settings - Fork 0
/
index.html
1405 lines (959 loc) · 135 KB
/
index.html
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
764
765
766
767
768
769
770
771
772
773
774
775
776
777
778
779
780
781
782
783
784
785
786
787
788
789
790
791
792
793
794
795
796
797
798
799
800
801
802
803
804
805
806
807
808
809
810
811
812
813
814
815
816
817
818
819
820
821
822
823
824
825
826
827
828
829
830
831
832
833
834
835
836
837
838
839
840
841
842
843
844
845
846
847
848
849
850
851
852
853
854
855
856
857
858
859
860
861
862
863
864
865
866
867
868
869
870
871
872
873
874
875
876
877
878
879
880
881
882
883
884
885
886
887
888
889
890
891
892
893
894
895
896
897
898
899
900
901
902
903
904
905
906
907
908
909
910
911
912
913
914
915
916
917
918
919
920
921
922
923
924
925
926
927
928
929
930
931
932
933
934
935
936
937
938
939
940
941
942
943
944
945
946
947
948
949
950
951
952
953
954
955
956
957
958
959
960
961
962
963
964
965
966
967
968
969
970
971
972
973
974
975
976
977
978
979
980
981
982
983
984
985
986
987
988
989
990
991
992
993
994
995
996
997
998
999
1000
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<meta name="viewport" content="width=device-width, initial-scale=1, maximum-scale=2">
<meta name="theme-color" content="#222">
<meta name="generator" content="Hexo 4.2.1">
<link rel="apple-touch-icon" sizes="180x180" href="/images/apple-touch-icon-next.png">
<link rel="icon" type="image/png" sizes="32x32" href="/images/favicon-32x32-next.png">
<link rel="icon" type="image/png" sizes="16x16" href="/images/favicon-16x16-next.png">
<link rel="mask-icon" href="/images/logo.svg" color="#222">
<link rel="stylesheet" href="/css/main.css">
<link rel="stylesheet" href="/lib/font-awesome/css/all.min.css">
<script id="hexo-configurations">
var NexT = window.NexT || {};
var CONFIG = {"hostname":"yonglife.com","root":"/","scheme":"Mist","version":"7.8.0","exturl":false,"sidebar":{"position":"left","display":"always","padding":18,"offset":12,"onmobile":false},"copycode":{"enable":false,"show_result":false,"style":null},"back2top":{"enable":true,"sidebar":false,"scrollpercent":false},"bookmark":{"enable":false,"color":"#222","save":"auto"},"fancybox":false,"mediumzoom":false,"lazyload":false,"pangu":false,"comments":{"style":"tabs","active":null,"storage":true,"lazyload":false,"nav":null},"algolia":{"hits":{"per_page":10},"labels":{"input_placeholder":"Search for Posts","hits_empty":"We didn't find any results for the search: ${query}","hits_stats":"${hits} results found in ${time} ms"}},"localsearch":{"enable":true,"trigger":"auto","top_n_per_article":1,"unescape":false,"preload":false},"motion":{"enable":true,"async":false,"transition":{"post_block":"fadeIn","post_header":"slideDownIn","post_body":"slideDownIn","coll_header":"slideLeftIn","sidebar":"slideUpIn"}},"path":"search.xml"};
</script>
<meta name="description" content="Record . Grow . Evolve">
<meta property="og:type" content="website">
<meta property="og:title" content="Yong's Blog">
<meta property="og:url" content="http://yonglife.com/index.html">
<meta property="og:site_name" content="Yong's Blog">
<meta property="og:description" content="Record . Grow . Evolve">
<meta property="og:locale" content="en_US">
<meta property="article:author" content="Yong Cao">
<meta name="twitter:card" content="summary">
<link rel="canonical" href="http://yonglife.com/">
<script id="page-configurations">
// https://hexo.io/docs/variables.html
CONFIG.page = {
sidebar: "",
isHome : true,
isPost : false,
lang : 'en'
};
</script>
<title>Yong's Blog</title>
<noscript>
<style>
.use-motion .brand,
.use-motion .menu-item,
.sidebar-inner,
.use-motion .post-block,
.use-motion .pagination,
.use-motion .comments,
.use-motion .post-header,
.use-motion .post-body,
.use-motion .collection-header { opacity: initial; }
.use-motion .site-title,
.use-motion .site-subtitle {
opacity: initial;
top: initial;
}
.use-motion .logo-line-before i { left: initial; }
.use-motion .logo-line-after i { right: initial; }
</style>
</noscript>
</head>
<body itemscope itemtype="http://schema.org/WebPage">
<div class="container use-motion">
<div class="headband"></div>
<header class="header" itemscope itemtype="http://schema.org/WPHeader">
<div class="header-inner"><div class="site-brand-container">
<div class="site-nav-toggle">
<div class="toggle" aria-label="Toggle navigation bar">
<span class="toggle-line toggle-line-first"></span>
<span class="toggle-line toggle-line-middle"></span>
<span class="toggle-line toggle-line-last"></span>
</div>
</div>
<div class="site-meta">
<a href="/" class="brand" rel="start">
<span class="logo-line-before"><i></i></span>
<h1 class="site-title">Yong's Blog</h1>
<span class="logo-line-after"><i></i></span>
</a>
</div>
<div class="site-nav-right">
<div class="toggle popup-trigger">
<i class="fa fa-search fa-fw fa-lg"></i>
</div>
</div>
</div>
<nav class="site-nav">
<ul id="menu" class="main-menu menu">
<li class="menu-item menu-item-home">
<a href="/" rel="section"><i class="fa fa-home fa-fw"></i>Home</a>
</li>
<li class="menu-item menu-item-tags">
<a href="/tags/" rel="section"><i class="fa fa-tags fa-fw"></i>Tags</a>
</li>
<li class="menu-item menu-item-categories">
<a href="/categories/" rel="section"><i class="fa fa-th fa-fw"></i>Categories</a>
</li>
<li class="menu-item menu-item-archives">
<a href="/archives/" rel="section"><i class="fa fa-archive fa-fw"></i>Archives</a>
</li>
<li class="menu-item menu-item-search">
<a role="button" class="popup-trigger"><i class="fa fa-search fa-fw"></i>Search
</a>
</li>
</ul>
</nav>
<div class="search-pop-overlay">
<div class="popup search-popup">
<div class="search-header">
<span class="search-icon">
<i class="fa fa-search"></i>
</span>
<div class="search-input-container">
<input autocomplete="off" autocapitalize="off"
placeholder="Searching..." spellcheck="false"
type="search" class="search-input">
</div>
<span class="popup-btn-close">
<i class="fa fa-times-circle"></i>
</span>
</div>
<div id="search-result">
<div id="no-result">
<i class="fa fa-spinner fa-pulse fa-5x fa-fw"></i>
</div>
</div>
</div>
</div>
</div>
</header>
<div class="back-to-top">
<i class="fa fa-arrow-up"></i>
<span>0%</span>
</div>
<main class="main">
<div class="main-inner">
<div class="content-wrap">
<div class="content index posts-expand">
<article itemscope itemtype="http://schema.org/Article" class="post-block" lang="en">
<link itemprop="mainEntityOfPage" href="http://yonglife.com/2022/05/22/Visitor-Pattern-in-Python/">
<span hidden itemprop="author" itemscope itemtype="http://schema.org/Person">
<meta itemprop="image" content="/images/headImage.jpg">
<meta itemprop="name" content="Yong Cao">
<meta itemprop="description" content="Record . Grow . Evolve">
</span>
<span hidden itemprop="publisher" itemscope itemtype="http://schema.org/Organization">
<meta itemprop="name" content="Yong's Blog">
</span>
<header class="post-header">
<h2 class="post-title" itemprop="name headline">
<a href="/2022/05/22/Visitor-Pattern-in-Python/" class="post-title-link" itemprop="url">Visitor Pattern in Python</a>
</h2>
<div class="post-meta">
<span class="post-meta-item">
<span class="post-meta-item-icon">
<i class="far fa-calendar"></i>
</span>
<span class="post-meta-item-text">Posted on</span>
<time title="Created: 2022-05-22 09:30:51 / Modified: 15:15:52" itemprop="dateCreated datePublished" datetime="2022-05-22T09:30:51-07:00">2022-05-22</time>
</span>
<span id="/2022/05/22/Visitor-Pattern-in-Python/" class="post-meta-item leancloud_visitors" data-flag-title="Visitor Pattern in Python" title="Views">
<span class="post-meta-item-icon">
<i class="fa fa-eye"></i>
</span>
<span class="post-meta-item-text">Views: </span>
<span class="leancloud-visitors-count"></span>
</span>
<span class="post-meta-item">
<span class="post-meta-item-icon">
<i class="far fa-comment"></i>
</span>
<span class="post-meta-item-text">Valine: </span>
<a title="valine" href="/2022/05/22/Visitor-Pattern-in-Python/#valine-comments" itemprop="discussionUrl">
<span class="post-comments-count valine-comment-count" data-xid="/2022/05/22/Visitor-Pattern-in-Python/" itemprop="commentCount"></span>
</a>
</span>
</div>
</header>
<div class="post-body" itemprop="articleBody">
<p>Quoting <a href="https://en.wikipedia.org/wiki/Visitor_pattern" target="_blank" rel="noopener">wikipedia</a></p>
<blockquote>
<p>In object-oriented programming and software engineering, the visitor design pattern is a way of separating an algorithm from an object structure on which it operates. A practical result of this separation is the ability to add new operations to existing object structures without modifying the structures. It is one way to follow the open/closed principle.</p>
</blockquote>
<p>As mentioned, the goal is to separate the algorithm from objects which it operates on.</p>
<p>As a result, it allow us to add new operations without modifying the objects.</p>
<h2 id="In-C"><a href="#In-C" class="headerlink" title="In C++"></a>In C++</h2><figure class="highlight cpp"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br></pre></td><td class="code"><pre><span class="line"><span class="comment">// ivisitor.h</span></span><br><span class="line"><span class="meta">#<span class="meta-keyword">ifndef</span> INCLUDE_VISITOR_H</span></span><br><span class="line"><span class="meta">#<span class="meta-keyword">define</span> INCLUDE_VISITOR_H</span></span><br><span class="line"></span><br><span class="line"><span class="class"><span class="keyword">struct</span> <span class="title">Rider</span>;</span></span><br><span class="line"><span class="class"><span class="keyword">struct</span> <span class="title">Skier</span>;</span></span><br><span class="line"></span><br><span class="line"><span class="class"><span class="keyword">struct</span> <span class="title">IVisitor</span> {</span></span><br><span class="line"> <span class="keyword">virtual</span> ~IVisitor() = <span class="keyword">default</span>;</span><br><span class="line"> <span class="function"><span class="keyword">virtual</span> <span class="keyword">void</span> <span class="title">visit</span><span class="params">(Rider *student)</span> </span>= <span class="number">0</span>;</span><br><span class="line"> <span class="function"><span class="keyword">virtual</span> <span class="keyword">void</span> <span class="title">visit</span><span class="params">(Skier *student)</span> </span>= <span class="number">0</span>;</span><br><span class="line">};</span><br><span class="line"></span><br><span class="line"><span class="meta">#<span class="meta-keyword">endif</span> <span class="comment">/* INCLUDE_VISITOR_H */</span></span></span><br></pre></td></tr></table></figure>
<figure class="highlight cpp"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br><span class="line">19</span><br><span class="line">20</span><br></pre></td><td class="code"><pre><span class="line"><span class="comment">// student.h</span></span><br><span class="line"><span class="meta">#<span class="meta-keyword">ifndef</span> INCLUDE_STUDENT_H</span></span><br><span class="line"><span class="meta">#<span class="meta-keyword">define</span> INCLUDE_STUDENT_H</span></span><br><span class="line"></span><br><span class="line"><span class="meta">#<span class="meta-keyword">include</span> <span class="meta-string">"ivisitor.h"</span></span></span><br><span class="line"></span><br><span class="line"><span class="class"><span class="keyword">struct</span> <span class="title">Student</span> {</span></span><br><span class="line"> <span class="keyword">virtual</span> ~Student() = <span class="keyword">default</span>;</span><br><span class="line"> <span class="function"><span class="keyword">virtual</span> <span class="keyword">void</span> <span class="title">accept</span><span class="params">(IVisitor *visitor)</span> </span>= <span class="number">0</span>;</span><br><span class="line">};</span><br><span class="line"></span><br><span class="line"><span class="class"><span class="keyword">struct</span> <span class="title">Skier</span> :</span> <span class="keyword">public</span> Student {</span><br><span class="line"> <span class="function"><span class="keyword">void</span> <span class="title">accept</span><span class="params">(IVisitor *visitor)</span> <span class="keyword">override</span> </span>{ visitor->visit(<span class="keyword">this</span>); } <span class="comment">// Second dispatch</span></span><br><span class="line">};</span><br><span class="line"></span><br><span class="line"><span class="class"><span class="keyword">struct</span> <span class="title">Rider</span> :</span> <span class="keyword">public</span> Student {</span><br><span class="line"> <span class="function"><span class="keyword">void</span> <span class="title">accept</span><span class="params">(IVisitor *visitor)</span> <span class="keyword">override</span> </span>{ visitor->visit(<span class="keyword">this</span>); } <span class="comment">// Second dispatch</span></span><br><span class="line">};</span><br><span class="line"></span><br><span class="line"><span class="meta">#<span class="meta-keyword">endif</span> <span class="comment">/* INCLUDE_STUDENT_H */</span></span></span><br></pre></td></tr></table></figure>
<figure class="highlight cpp"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br><span class="line">19</span><br><span class="line">20</span><br><span class="line">21</span><br><span class="line">22</span><br><span class="line">23</span><br><span class="line">24</span><br><span class="line">25</span><br><span class="line">26</span><br><span class="line">27</span><br><span class="line">28</span><br><span class="line">29</span><br><span class="line">30</span><br><span class="line">31</span><br><span class="line">32</span><br><span class="line">33</span><br></pre></td><td class="code"><pre><span class="line"><span class="comment">// main.cc</span></span><br><span class="line"><span class="meta">#<span class="meta-keyword">include</span> <span class="meta-string">"student.h"</span></span></span><br><span class="line"><span class="meta">#<span class="meta-keyword">include</span> <span class="meta-string">"student_visitor.h"</span></span></span><br><span class="line"><span class="meta">#<span class="meta-keyword">include</span> <span class="meta-string"><iostream></span></span></span><br><span class="line"><span class="meta">#<span class="meta-keyword">include</span> <span class="meta-string"><memory></span></span></span><br><span class="line"><span class="meta">#<span class="meta-keyword">include</span> <span class="meta-string"><vector></span></span></span><br><span class="line"></span><br><span class="line"><span class="keyword">using</span> <span class="keyword">namespace</span> <span class="built_in">std</span>;</span><br><span class="line"></span><br><span class="line"><span class="class"><span class="keyword">struct</span> <span class="title">RentalVisitor</span> :</span> IVisitor {</span><br><span class="line"> <span class="function"><span class="keyword">void</span> <span class="title">visit</span><span class="params">(Rider *rider)</span> </span>{ <span class="built_in">std</span>::<span class="built_in">cout</span> << <span class="string">"Prepare snowboard..."</span> << <span class="built_in">std</span>::<span class="built_in">endl</span>; }</span><br><span class="line"> <span class="function"><span class="keyword">void</span> <span class="title">visit</span><span class="params">(Skier *skier)</span> </span>{ <span class="built_in">std</span>::<span class="built_in">cout</span> << <span class="string">"Prepare ski..."</span> << <span class="built_in">std</span>::<span class="built_in">endl</span>; };</span><br><span class="line">};</span><br><span class="line"></span><br><span class="line"><span class="class"><span class="keyword">struct</span> <span class="title">TeachVisitor</span> :</span> IVisitor {</span><br><span class="line"> <span class="function"><span class="keyword">void</span> <span class="title">visit</span><span class="params">(Rider *rider)</span> </span>{ <span class="built_in">std</span>::<span class="built_in">cout</span> << <span class="string">"Teach a rider"</span> << <span class="built_in">std</span>::<span class="built_in">endl</span>; }</span><br><span class="line"> <span class="function"><span class="keyword">void</span> <span class="title">visit</span><span class="params">(Skier *skier)</span> </span>{ <span class="built_in">std</span>::<span class="built_in">cout</span> << <span class="string">"Teach a skier"</span> << <span class="built_in">std</span>::<span class="built_in">endl</span>; };</span><br><span class="line">};</span><br><span class="line"></span><br><span class="line"><span class="comment">// Add new visitor to perform new functionality</span></span><br><span class="line"></span><br><span class="line"><span class="function"><span class="keyword">int</span> <span class="title">main</span><span class="params">(<span class="keyword">int</span>, <span class="keyword">char</span> **)</span> </span>{</span><br><span class="line"> <span class="built_in">vector</span><<span class="built_in">unique_ptr</span><Student>> students;</span><br><span class="line"> students.emplace_back(make_unique<Skier>());</span><br><span class="line"> students.emplace_back(make_unique<Rider>());</span><br><span class="line"></span><br><span class="line"> RentalVisitor rental_visitor;</span><br><span class="line"> TeachVisitor teach_visitor;</span><br><span class="line"> <span class="keyword">for</span> (<span class="keyword">auto</span> &s : students) {</span><br><span class="line"> s->accept(&rental_visitor); <span class="comment">// First dispatch</span></span><br><span class="line"> s->accept(&teach_visitor); <span class="comment">// First dispatch</span></span><br><span class="line"> }</span><br><span class="line">}</span><br></pre></td></tr></table></figure>
<h2 id="In-Python"><a href="#In-Python" class="headerlink" title="In Python"></a>In Python</h2><h3 id="Traditional-double-dispatch"><a href="#Traditional-double-dispatch" class="headerlink" title="Traditional double dispatch"></a>Traditional double dispatch</h3><figure class="highlight py"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br><span class="line">19</span><br><span class="line">20</span><br><span class="line">21</span><br><span class="line">22</span><br><span class="line">23</span><br><span class="line">24</span><br><span class="line">25</span><br><span class="line">26</span><br><span class="line">27</span><br><span class="line">28</span><br><span class="line">29</span><br><span class="line">30</span><br><span class="line">31</span><br><span class="line">32</span><br><span class="line">33</span><br><span class="line">34</span><br><span class="line">35</span><br><span class="line">36</span><br><span class="line">37</span><br><span class="line">38</span><br><span class="line">39</span><br><span class="line">40</span><br><span class="line">41</span><br><span class="line">42</span><br><span class="line">43</span><br><span class="line">44</span><br><span class="line">45</span><br><span class="line">46</span><br><span class="line">47</span><br><span class="line">48</span><br><span class="line">49</span><br><span class="line">50</span><br><span class="line">51</span><br><span class="line">52</span><br><span class="line">53</span><br><span class="line">54</span><br><span class="line">55</span><br><span class="line">56</span><br><span class="line">57</span><br><span class="line">58</span><br><span class="line">59</span><br><span class="line">60</span><br><span class="line">61</span><br><span class="line">62</span><br><span class="line">63</span><br><span class="line">64</span><br><span class="line">65</span><br><span class="line">66</span><br><span class="line">67</span><br><span class="line">68</span><br><span class="line">69</span><br><span class="line">70</span><br></pre></td><td class="code"><pre><span class="line"><span class="string">'''</span></span><br><span class="line"><span class="string">Implement visitor pattern via double dispatch.</span></span><br><span class="line"><span class="string">'''</span></span><br><span class="line"><span class="keyword">from</span> __future__ <span class="keyword">import</span> annotations</span><br><span class="line"></span><br><span class="line"><span class="keyword">from</span> abc <span class="keyword">import</span> ABC, abstractmethod</span><br><span class="line"><span class="keyword">from</span> typing <span class="keyword">import</span> List</span><br><span class="line"></span><br><span class="line"></span><br><span class="line"><span class="class"><span class="keyword">class</span> <span class="title">IVisitor</span><span class="params">(ABC)</span>:</span></span><br><span class="line"> <span class="string">'''</span></span><br><span class="line"><span class="string"> Visitor interface</span></span><br><span class="line"><span class="string"> '''</span></span><br><span class="line"><span class="meta"> @abstractmethod</span></span><br><span class="line"> <span class="function"><span class="keyword">def</span> <span class="title">visit_skier</span><span class="params">(self, student)</span>:</span></span><br><span class="line"> ...</span><br><span class="line"></span><br><span class="line"><span class="meta"> @abstractmethod</span></span><br><span class="line"> <span class="function"><span class="keyword">def</span> <span class="title">visit_rider</span><span class="params">(self, student)</span>:</span></span><br><span class="line"> ...</span><br><span class="line"></span><br><span class="line"></span><br><span class="line"><span class="class"><span class="keyword">class</span> <span class="title">Student</span><span class="params">(ABC)</span>:</span></span><br><span class="line"><span class="meta"> @abstractmethod</span></span><br><span class="line"> <span class="function"><span class="keyword">def</span> <span class="title">accept</span><span class="params">(self, visitor)</span>:</span></span><br><span class="line"> ...</span><br><span class="line"></span><br><span class="line"></span><br><span class="line"><span class="class"><span class="keyword">class</span> <span class="title">Skier</span><span class="params">(Student)</span>:</span></span><br><span class="line"> <span class="function"><span class="keyword">def</span> <span class="title">accept</span><span class="params">(self, visitor)</span>:</span></span><br><span class="line"> visitor.visit_skier(self)</span><br><span class="line"></span><br><span class="line"></span><br><span class="line"><span class="class"><span class="keyword">class</span> <span class="title">Rider</span><span class="params">(Student)</span>:</span></span><br><span class="line"> <span class="function"><span class="keyword">def</span> <span class="title">accept</span><span class="params">(self, visitor)</span>:</span></span><br><span class="line"> visitor.visit_rider(self)</span><br><span class="line"></span><br><span class="line"></span><br><span class="line"><span class="comment">#</span></span><br><span class="line"><span class="comment"># Concrate visitors</span></span><br><span class="line"><span class="comment">#</span></span><br><span class="line"><span class="class"><span class="keyword">class</span> <span class="title">RentalVisitor</span><span class="params">(IVisitor)</span>:</span></span><br><span class="line"> <span class="function"><span class="keyword">def</span> <span class="title">visit_skier</span><span class="params">(self, student)</span>:</span></span><br><span class="line"> print(<span class="string">'Prepare ski...'</span>)</span><br><span class="line"></span><br><span class="line"> <span class="function"><span class="keyword">def</span> <span class="title">visit_rider</span><span class="params">(self, student)</span>:</span></span><br><span class="line"> print(<span class="string">'Prepare snowboard...'</span>)</span><br><span class="line"></span><br><span class="line"></span><br><span class="line"><span class="class"><span class="keyword">class</span> <span class="title">TeachVisitor</span><span class="params">(IVisitor)</span>:</span></span><br><span class="line"> <span class="function"><span class="keyword">def</span> <span class="title">visit_skier</span><span class="params">(self, student)</span>:</span></span><br><span class="line"> print(<span class="string">'Teach skier...'</span>)</span><br><span class="line"></span><br><span class="line"> <span class="function"><span class="keyword">def</span> <span class="title">visit_rider</span><span class="params">(self, student)</span>:</span></span><br><span class="line"> print(<span class="string">'Teach rider...'</span>)</span><br><span class="line"></span><br><span class="line"><span class="comment"># Add new visitor to perform new functionality</span></span><br><span class="line"></span><br><span class="line"><span class="function"><span class="keyword">def</span> <span class="title">main</span><span class="params">()</span>:</span></span><br><span class="line"> rental_visitor = RentalVisitor()</span><br><span class="line"> teach_visitor = TeachVisitor()</span><br><span class="line"></span><br><span class="line"> students: List[Student] = [Skier(), Skier(), Rider()]</span><br><span class="line"> <span class="keyword">for</span> s <span class="keyword">in</span> students:</span><br><span class="line"> s.accept(rental_visitor)</span><br><span class="line"> s.accept(teach_visitor)</span><br><span class="line"></span><br><span class="line"></span><br><span class="line"><span class="keyword">if</span> __name__ == <span class="string">"__main__"</span>:</span><br><span class="line"> main()</span><br></pre></td></tr></table></figure>
<h3 id="Annotation"><a href="#Annotation" class="headerlink" title="Annotation"></a>Annotation</h3><figure class="highlight py"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br><span class="line">19</span><br><span class="line">20</span><br><span class="line">21</span><br><span class="line">22</span><br><span class="line">23</span><br><span class="line">24</span><br><span class="line">25</span><br><span class="line">26</span><br><span class="line">27</span><br><span class="line">28</span><br><span class="line">29</span><br><span class="line">30</span><br><span class="line">31</span><br><span class="line">32</span><br><span class="line">33</span><br><span class="line">34</span><br><span class="line">35</span><br><span class="line">36</span><br><span class="line">37</span><br><span class="line">38</span><br><span class="line">39</span><br><span class="line">40</span><br><span class="line">41</span><br><span class="line">42</span><br><span class="line">43</span><br><span class="line">44</span><br><span class="line">45</span><br><span class="line">46</span><br><span class="line">47</span><br><span class="line">48</span><br><span class="line">49</span><br><span class="line">50</span><br><span class="line">51</span><br><span class="line">52</span><br><span class="line">53</span><br><span class="line">54</span><br><span class="line">55</span><br><span class="line">56</span><br><span class="line">57</span><br><span class="line">58</span><br><span class="line">59</span><br><span class="line">60</span><br><span class="line">61</span><br><span class="line">62</span><br><span class="line">63</span><br><span class="line">64</span><br><span class="line">65</span><br><span class="line">66</span><br><span class="line">67</span><br><span class="line">68</span><br><span class="line">69</span><br><span class="line">70</span><br><span class="line">71</span><br><span class="line">72</span><br><span class="line">73</span><br><span class="line">74</span><br><span class="line">75</span><br><span class="line">76</span><br><span class="line">77</span><br><span class="line">78</span><br></pre></td><td class="code"><pre><span class="line"><span class="keyword">from</span> __future__ <span class="keyword">import</span> annotations</span><br><span class="line"></span><br><span class="line"><span class="keyword">from</span> abc <span class="keyword">import</span> ABC, abstractmethod</span><br><span class="line"><span class="keyword">from</span> typing <span class="keyword">import</span> List</span><br><span class="line"></span><br><span class="line"></span><br><span class="line"><span class="class"><span class="keyword">class</span> <span class="title">Student</span><span class="params">(ABC)</span>:</span></span><br><span class="line"> ...</span><br><span class="line"></span><br><span class="line"></span><br><span class="line"><span class="class"><span class="keyword">class</span> <span class="title">Skier</span><span class="params">(Student)</span>:</span></span><br><span class="line"> ...</span><br><span class="line"></span><br><span class="line"></span><br><span class="line"><span class="class"><span class="keyword">class</span> <span class="title">Rider</span><span class="params">(Student)</span>:</span></span><br><span class="line"> ...</span><br><span class="line"></span><br><span class="line"></span><br><span class="line"><span class="comment"># A couple helper functions first</span></span><br><span class="line"></span><br><span class="line"><span class="function"><span class="keyword">def</span> <span class="title">_qualname</span><span class="params">(obj)</span>:</span></span><br><span class="line"> <span class="string">'''Get the fully-qualified name of an object (including module).'''</span></span><br><span class="line"> <span class="keyword">return</span> obj.__module__ + <span class="string">'.'</span> + obj.__qualname__</span><br><span class="line"></span><br><span class="line"></span><br><span class="line"><span class="function"><span class="keyword">def</span> <span class="title">_declaring_class</span><span class="params">(obj)</span>:</span></span><br><span class="line"> <span class="string">'''Get the name of the class that declared an object.'''</span></span><br><span class="line"> name = _qualname(obj)</span><br><span class="line"> <span class="keyword">return</span> name[:name.rfind(<span class="string">'.'</span>)]</span><br><span class="line"></span><br><span class="line"></span><br><span class="line"><span class="comment"># Stores the actual visitor methods</span></span><br><span class="line">_methods = {}</span><br><span class="line"></span><br><span class="line"></span><br><span class="line"><span class="function"><span class="keyword">def</span> <span class="title">_visitor_impl</span><span class="params">(self, arg)</span>:</span></span><br><span class="line"> <span class="string">'''Actual visitor method implementation.'''</span></span><br><span class="line"> method = _methods[(_qualname(type(self)), type(arg))]</span><br><span class="line"> <span class="keyword">return</span> method(self, arg)</span><br><span class="line"></span><br><span class="line"></span><br><span class="line"><span class="function"><span class="keyword">def</span> <span class="title">visitor</span><span class="params">(arg_type)</span>:</span></span><br><span class="line"> <span class="string">'''Decorator that creates a visitor method.'''</span></span><br><span class="line"></span><br><span class="line"> <span class="function"><span class="keyword">def</span> <span class="title">decorator</span><span class="params">(fn)</span>:</span></span><br><span class="line"> declaring_class = _declaring_class(fn)</span><br><span class="line"> _methods[(declaring_class, arg_type)] = fn</span><br><span class="line"></span><br><span class="line"> <span class="comment"># Replace all decorated methods with _visitor_impl</span></span><br><span class="line"> <span class="keyword">return</span> _visitor_impl</span><br><span class="line"></span><br><span class="line"> <span class="keyword">return</span> decorator</span><br><span class="line"></span><br><span class="line"></span><br><span class="line"><span class="class"><span class="keyword">class</span> <span class="title">RentalVisitor</span>:</span></span><br><span class="line"><span class="meta"> @visitor(Skier)</span></span><br><span class="line"> <span class="function"><span class="keyword">def</span> <span class="title">visit</span><span class="params">(self, student)</span>:</span></span><br><span class="line"> print(<span class="string">'Prepare ski...'</span>)</span><br><span class="line"></span><br><span class="line"><span class="meta"> @visitor(Rider)</span></span><br><span class="line"> <span class="function"><span class="keyword">def</span> <span class="title">visit</span><span class="params">(self, student)</span>:</span></span><br><span class="line"> print(<span class="string">'Prepare snowboard...'</span>)</span><br><span class="line"></span><br><span class="line"></span><br><span class="line"><span class="comment"># Add new visitor to perform new functionality</span></span><br><span class="line"></span><br><span class="line"><span class="function"><span class="keyword">def</span> <span class="title">main</span><span class="params">()</span>:</span></span><br><span class="line"> rental_visitor = RentalVisitor()</span><br><span class="line"></span><br><span class="line"> students: List[Student] = [Skier(), Skier(), Rider()]</span><br><span class="line"> <span class="keyword">for</span> s <span class="keyword">in</span> students:</span><br><span class="line"> rental_visitor.visit(s)</span><br><span class="line"> </span><br><span class="line"> print(_methods)</span><br><span class="line"></span><br><span class="line"></span><br><span class="line"><span class="keyword">if</span> __name__ == <span class="string">'__main__'</span>:</span><br><span class="line"> main()</span><br></pre></td></tr></table></figure>
</div>
<footer class="post-footer">
<div class="post-eof"></div>
</footer>
</article>
<article itemscope itemtype="http://schema.org/Article" class="post-block" lang="en">
<link itemprop="mainEntityOfPage" href="http://yonglife.com/2021/10/03/Empty-the-inbox-of-your-email/">
<span hidden itemprop="author" itemscope itemtype="http://schema.org/Person">
<meta itemprop="image" content="/images/headImage.jpg">
<meta itemprop="name" content="Yong Cao">
<meta itemprop="description" content="Record . Grow . Evolve">
</span>
<span hidden itemprop="publisher" itemscope itemtype="http://schema.org/Organization">
<meta itemprop="name" content="Yong's Blog">
</span>
<header class="post-header">
<h2 class="post-title" itemprop="name headline">
<a href="/2021/10/03/Empty-the-inbox-of-your-email/" class="post-title-link" itemprop="url">Empty the inbox of your email</a>
</h2>
<div class="post-meta">
<span class="post-meta-item">
<span class="post-meta-item-icon">
<i class="far fa-calendar"></i>
</span>
<span class="post-meta-item-text">Posted on</span>
<time title="Created: 2021-10-03 14:19:12 / Modified: 12:25:32" itemprop="dateCreated datePublished" datetime="2021-10-03T14:19:12-07:00">2021-10-03</time>
</span>
<span class="post-meta-item">
<span class="post-meta-item-icon">
<i class="far fa-folder"></i>
</span>
<span class="post-meta-item-text">In</span>
<span itemprop="about" itemscope itemtype="http://schema.org/Thing">
<a href="/categories/Program/" itemprop="url" rel="index"><span itemprop="name">Program</span></a>
</span>
</span>
<span id="/2021/10/03/Empty-the-inbox-of-your-email/" class="post-meta-item leancloud_visitors" data-flag-title="Empty the inbox of your email" title="Views">
<span class="post-meta-item-icon">
<i class="fa fa-eye"></i>
</span>
<span class="post-meta-item-text">Views: </span>
<span class="leancloud-visitors-count"></span>
</span>
<span class="post-meta-item">
<span class="post-meta-item-icon">
<i class="far fa-comment"></i>
</span>
<span class="post-meta-item-text">Valine: </span>
<a title="valine" href="/2021/10/03/Empty-the-inbox-of-your-email/#valine-comments" itemprop="discussionUrl">
<span class="post-comments-count valine-comment-count" data-xid="/2021/10/03/Empty-the-inbox-of-your-email/" itemprop="commentCount"></span>
</a>
</span>
</div>
</header>
<div class="post-body" itemprop="articleBody">
<p>To briefly explain why we want to empty the inbox and methods to quickly archive<br>hundreds or thousands emails if your already accumulated.</p>
<h1 id="WHY"><a href="#WHY" class="headerlink" title="WHY"></a>WHY</h1><p>Just google <code>Empty email inbox</code>, you will find lots of articles talk about why<br>you want to do it. In short, you needs empty inbox by archiving emails for </p>
<ul>
<li>Organization<ul>
<li>get rid of junk </li>
<li>unsubscribe from emails you do not want</li>
</ul>
</li>
<li>Feeling in control</li>
<li>Not missing important email </li>
<li>Efficiency<ul>
<li>Force to make decision when receiving new email</li>
</ul>
</li>
</ul>
<p>To those who are new to <code>Archive</code>, you will not lose any email by archiving it.<br>Archived emails can always be found in <code>All mails</code>.</p>
<h1 id="HOW-for-gmail-users"><a href="#HOW-for-gmail-users" class="headerlink" title="HOW - for gmail users."></a>HOW - for gmail users.</h1><h2 id="Manually"><a href="#Manually" class="headerlink" title="Manually"></a>Manually</h2><p>In gmail, setup following configs</p>
<ul>
<li><code>[All settings]</code> -> <code>[General]</code>: <code>Maximum page size: 100</code></li>
<li><code>[All settings]</code> -> <code>[General]</code>: <code>Keyboard shortcuts: ON</code></li>
</ul>
<p>Now, you can archive emails from your inbox with shortcut.</p>
<ul>
<li><code>* + a</code> to select all emails.</li>
<li><code>e</code> to archive selected emails.</li>
</ul>
<p>Repeated above steps until your inbox is empty.</p>
<h2 id="Automation-with-Apple-Script"><a href="#Automation-with-Apple-Script" class="headerlink" title="Automation with Apple Script"></a>Automation with Apple Script</h2><p>If you have couple thousands of email, the manual procedures will be quite annoying.<br>We can automate that with <code>Apple Script</code> if you are using MacOS.</p>
<ul>
<li>Open MacOS embedded application <code>Automator</code></li>
<li>Click <code>New Document</code></li>
<li>Select <code>Quick Action</code> as type of new document</li>
<li>Click <code>Choose</code></li>
<li>Change <code>Workflow receives current</code> to <code>no input</code></li>
<li>Click <code>Record</code></li>
<li>Open <code>gmail</code> in your browser and repeat steps in above section to archive 100 emails</li>
<li>Click <code>STOP</code> button in <code>Automator</code>‘s popup</li>
<li>Modify script to repeat the recorded operations</li>
</ul>
<p>Please check this <a href="https://youtu.be/J4nj13T7Iqk" target="_blank" rel="noopener">video</a>, for details.</p>
</div>
<footer class="post-footer">
<div class="post-eof"></div>
</footer>
</article>
<article itemscope itemtype="http://schema.org/Article" class="post-block" lang="en">
<link itemprop="mainEntityOfPage" href="http://yonglife.com/2020/10/10/Fundamental-Algorithm-Knowledge/">
<span hidden itemprop="author" itemscope itemtype="http://schema.org/Person">
<meta itemprop="image" content="/images/headImage.jpg">
<meta itemprop="name" content="Yong Cao">
<meta itemprop="description" content="Record . Grow . Evolve">
</span>
<span hidden itemprop="publisher" itemscope itemtype="http://schema.org/Organization">
<meta itemprop="name" content="Yong's Blog">
</span>
<header class="post-header">
<h2 class="post-title" itemprop="name headline">
<a href="/2020/10/10/Fundamental-Algorithm-Knowledge/" class="post-title-link" itemprop="url">Fundamental Algorithm Knowledge</a>
</h2>
<div class="post-meta">
<span class="post-meta-item">
<span class="post-meta-item-icon">
<i class="far fa-calendar"></i>
</span>
<span class="post-meta-item-text">Posted on</span>
<time title="Created: 2020-10-10 17:30:46 / Modified: 18:58:39" itemprop="dateCreated datePublished" datetime="2020-10-10T17:30:46-07:00">2020-10-10</time>
</span>
<span id="/2020/10/10/Fundamental-Algorithm-Knowledge/" class="post-meta-item leancloud_visitors" data-flag-title="Fundamental Algorithm Knowledge" title="Views">
<span class="post-meta-item-icon">
<i class="fa fa-eye"></i>
</span>
<span class="post-meta-item-text">Views: </span>
<span class="leancloud-visitors-count"></span>
</span>
<span class="post-meta-item">
<span class="post-meta-item-icon">
<i class="far fa-comment"></i>
</span>
<span class="post-meta-item-text">Valine: </span>
<a title="valine" href="/2020/10/10/Fundamental-Algorithm-Knowledge/#valine-comments" itemprop="discussionUrl">
<span class="post-comments-count valine-comment-count" data-xid="/2020/10/10/Fundamental-Algorithm-Knowledge/" itemprop="commentCount"></span>
</a>
</span>
</div>
</header>
<div class="post-body" itemprop="articleBody">
<blockquote>
<p>If all you have is a hammer, everything looks like a nail </p>
<pre><code>- Abraham Maslow, 1962
</code></pre></blockquote>
<h1 id="List-Stack-LinkedList"><a href="#List-Stack-LinkedList" class="headerlink" title="List, Stack, LinkedList"></a>List, Stack, LinkedList</h1><h2 id="Binary-Search"><a href="#Binary-Search" class="headerlink" title="Binary Search"></a>Binary Search</h2><h2 id="Heap-Priority-Queue"><a href="#Heap-Priority-Queue" class="headerlink" title="Heap, Priority Queue"></a>Heap, Priority Queue</h2><h2 id="Sliding-Window"><a href="#Sliding-Window" class="headerlink" title="Sliding Window"></a>Sliding Window</h2><h3 id="Monotonic-Stack"><a href="#Monotonic-Stack" class="headerlink" title="Monotonic Stack"></a>Monotonic Stack</h3><h3 id="Monotonic-Queue"><a href="#Monotonic-Queue" class="headerlink" title="Monotonic Queue"></a>Monotonic Queue</h3><h2 id="Rare-technique"><a href="#Rare-technique" class="headerlink" title="Rare technique"></a>Rare technique</h2><ol>
<li>KMP</li>
<li>Manacher’s algorithm</li>
</ol>
<h1 id="Tree"><a href="#Tree" class="headerlink" title="Tree"></a>Tree</h1><h2 id="DFS"><a href="#DFS" class="headerlink" title="DFS"></a>DFS</h2><h2 id="BFS"><a href="#BFS" class="headerlink" title="BFS"></a>BFS</h2><h2 id="Trie"><a href="#Trie" class="headerlink" title="Trie"></a>Trie</h2><h2 id="Advanced-Tree"><a href="#Advanced-Tree" class="headerlink" title="Advanced Tree"></a>Advanced Tree</h2><h3 id="Binary-Index-Tree-Fenwick-Tree"><a href="#Binary-Index-Tree-Fenwick-Tree" class="headerlink" title="Binary Index Tree (Fenwick Tree)"></a>Binary Index Tree (Fenwick Tree)</h3><h3 id="Segment-Tree"><a href="#Segment-Tree" class="headerlink" title="Segment Tree"></a>Segment Tree</h3><h3 id="Self-Balanced-Tree-RB-Tree"><a href="#Self-Balanced-Tree-RB-Tree" class="headerlink" title="Self-Balanced Tree, RB Tree"></a>Self-Balanced Tree, RB Tree</h3><h1 id="Union-Find"><a href="#Union-Find" class="headerlink" title="Union-Find"></a>Union-Find</h1><h1 id="Graph"><a href="#Graph" class="headerlink" title="Graph"></a>Graph</h1><h2 id="DFS-BFS"><a href="#DFS-BFS" class="headerlink" title="DFS/BFS"></a>DFS/BFS</h2><h2 id="Cycle-Detection"><a href="#Cycle-Detection" class="headerlink" title="Cycle Detection"></a>Cycle Detection</h2><h2 id="Topologic-Sort"><a href="#Topologic-Sort" class="headerlink" title="Topologic Sort"></a>Topologic Sort</h2><h2 id="Euler-Path"><a href="#Euler-Path" class="headerlink" title="Euler Path"></a>Euler Path</h2><h2 id="Shortest-Path"><a href="#Shortest-Path" class="headerlink" title="Shortest Path"></a>Shortest Path</h2><h3 id="Dijkstra"><a href="#Dijkstra" class="headerlink" title="Dijkstra"></a>Dijkstra</h3><h3 id="Bellman-Ford"><a href="#Bellman-Ford" class="headerlink" title="Bellman-Ford"></a>Bellman-Ford</h3><h3 id="Floyd-Warshall"><a href="#Floyd-Warshall" class="headerlink" title="Floyd-Warshall"></a>Floyd-Warshall</h3><h2 id="Minimal-Spanning-Tree"><a href="#Minimal-Spanning-Tree" class="headerlink" title="Minimal Spanning Tree"></a>Minimal Spanning Tree</h2><h3 id="Kruskal’s-Algorithm"><a href="#Kruskal’s-Algorithm" class="headerlink" title="Kruskal’s Algorithm"></a>Kruskal’s Algorithm</h3><h3 id="Prim’s-Algorithm"><a href="#Prim’s-Algorithm" class="headerlink" title="Prim’s Algorithm"></a>Prim’s Algorithm</h3><h2 id="Tarjan’s-Algorithm"><a href="#Tarjan’s-Algorithm" class="headerlink" title="Tarjan’s Algorithm"></a>Tarjan’s Algorithm</h2><h3 id="Strong-Connected-Component"><a href="#Strong-Connected-Component" class="headerlink" title="Strong Connected Component"></a>Strong Connected Component</h3><h3 id="Cutting-Edge"><a href="#Cutting-Edge" class="headerlink" title="Cutting Edge"></a>Cutting Edge</h3><h3 id="Cutting-Point"><a href="#Cutting-Point" class="headerlink" title="Cutting Point"></a>Cutting Point</h3><h1 id="Dynamic-Programming"><a href="#Dynamic-Programming" class="headerlink" title="Dynamic Programming"></a>Dynamic Programming</h1><h2 id="Bit-Mask"><a href="#Bit-Mask" class="headerlink" title="Bit Mask"></a>Bit Mask</h2><p>## </p>
<h1 id="uncategorized"><a href="#uncategorized" class="headerlink" title="uncategorized"></a>uncategorized</h1><ol>
<li>Binary Lifting</li>
</ol>
</div>
<footer class="post-footer">
<div class="post-eof"></div>
</footer>
</article>
<article itemscope itemtype="http://schema.org/Article" class="post-block" lang="en">
<link itemprop="mainEntityOfPage" href="http://yonglife.com/2020/09/27/Essential-Graph-Algorithms/">
<span hidden itemprop="author" itemscope itemtype="http://schema.org/Person">
<meta itemprop="image" content="/images/headImage.jpg">
<meta itemprop="name" content="Yong Cao">
<meta itemprop="description" content="Record . Grow . Evolve">
</span>
<span hidden itemprop="publisher" itemscope itemtype="http://schema.org/Organization">
<meta itemprop="name" content="Yong's Blog">
</span>
<header class="post-header">
<h2 class="post-title" itemprop="name headline">
<a href="/2020/09/27/Essential-Graph-Algorithms/" class="post-title-link" itemprop="url">Essential Graph Algorithms</a>
</h2>
<div class="post-meta">
<span class="post-meta-item">
<span class="post-meta-item-icon">
<i class="far fa-calendar"></i>
</span>
<span class="post-meta-item-text">Posted on</span>
<time title="Created: 2020-09-27 11:08:11" itemprop="dateCreated datePublished" datetime="2020-09-27T11:08:11-07:00">2020-09-27</time>
</span>
<span class="post-meta-item">
<span class="post-meta-item-icon">
<i class="far fa-calendar-check"></i>
</span>
<span class="post-meta-item-text">Edited on</span>
<time title="Modified: 2020-11-08 14:38:51" itemprop="dateModified" datetime="2020-11-08T14:38:51-08:00">2020-11-08</time>
</span>
<span class="post-meta-item">
<span class="post-meta-item-icon">
<i class="far fa-folder"></i>
</span>
<span class="post-meta-item-text">In</span>
<span itemprop="about" itemscope itemtype="http://schema.org/Thing">
<a href="/categories/Program/" itemprop="url" rel="index"><span itemprop="name">Program</span></a>
</span>
</span>
<span id="/2020/09/27/Essential-Graph-Algorithms/" class="post-meta-item leancloud_visitors" data-flag-title="Essential Graph Algorithms" title="Views">
<span class="post-meta-item-icon">
<i class="fa fa-eye"></i>
</span>
<span class="post-meta-item-text">Views: </span>
<span class="leancloud-visitors-count"></span>
</span>
<span class="post-meta-item">
<span class="post-meta-item-icon">
<i class="far fa-comment"></i>
</span>
<span class="post-meta-item-text">Valine: </span>
<a title="valine" href="/2020/09/27/Essential-Graph-Algorithms/#valine-comments" itemprop="discussionUrl">
<span class="post-comments-count valine-comment-count" data-xid="/2020/09/27/Essential-Graph-Algorithms/" itemprop="commentCount"></span>
</a>
</span>
</div>
</header>
<div class="post-body" itemprop="articleBody">
<a id="more"></a>
<h1 id="What-is-a-Graph"><a href="#What-is-a-Graph" class="headerlink" title="What is a Graph"></a>What is a Graph</h1><h2 id="Non-directed"><a href="#Non-directed" class="headerlink" title="Non-directed"></a>Non-directed</h2><h2 id="Directed"><a href="#Directed" class="headerlink" title="Directed"></a>Directed</h2><h1 id="Cycle-Detection"><a href="#Cycle-Detection" class="headerlink" title="Cycle Detection"></a>Cycle Detection</h1><h2 id="Non-directed-Graph"><a href="#Non-directed-Graph" class="headerlink" title="Non-directed Graph"></a>Non-directed Graph</h2><h3 id="Union-Find"><a href="#Union-Find" class="headerlink" title="Union-Find"></a>Union-Find</h3><figure class="highlight python"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br><span class="line">19</span><br><span class="line">20</span><br><span class="line">21</span><br><span class="line">22</span><br><span class="line">23</span><br><span class="line">24</span><br><span class="line">25</span><br><span class="line">26</span><br><span class="line">27</span><br><span class="line">28</span><br></pre></td><td class="code"><pre><span class="line"><span class="class"><span class="keyword">class</span> <span class="title">UF</span>:</span></span><br><span class="line"> <span class="function"><span class="keyword">def</span> <span class="title">__init__</span><span class="params">(self)</span>:</span></span><br><span class="line"> self.uf = {}</span><br><span class="line"> </span><br><span class="line"> <span class="function"><span class="keyword">def</span> <span class="title">find</span><span class="params">(self, x: int)</span> -> int:</span></span><br><span class="line"> uf = self.uf</span><br><span class="line"> uf.setdefault(x, x)</span><br><span class="line"> <span class="keyword">if</span> uf[x] != x:</span><br><span class="line"> uf[x] = self.find(uf[x])</span><br><span class="line"> <span class="keyword">return</span> uf[x]</span><br><span class="line"> </span><br><span class="line"> <span class="function"><span class="keyword">def</span> <span class="title">union</span><span class="params">(self, x: int, y: int)</span> -> <span class="keyword">None</span>:</span></span><br><span class="line"> <span class="comment"># x -> y</span></span><br><span class="line"> uf = self.uf</span><br><span class="line"> uf[self.find(x)] = self.find(y)</span><br><span class="line"></span><br><span class="line"><span class="function"><span class="keyword">def</span> <span class="title">detect_cycle</span><span class="params">(n: int, edges: List[Tuple[int, int]])</span> -> bool:</span></span><br><span class="line"> uf = UF()</span><br><span class="line"></span><br><span class="line"> <span class="keyword">for</span> u, v <span class="keyword">in</span> edges:</span><br><span class="line"> <span class="keyword">if</span> uf.find(u) == uf.find(v):</span><br><span class="line"> <span class="keyword">return</span> <span class="literal">True</span></span><br><span class="line"> uf.union(u, v)</span><br><span class="line"> </span><br><span class="line"> <span class="keyword">return</span> <span class="literal">False</span> </span><br><span class="line"></span><br><span class="line"><span class="keyword">assert</span> <span class="literal">True</span> == detect_cycle(<span class="number">4</span>, [(<span class="number">0</span>, <span class="number">2</span>), (<span class="number">1</span>, <span class="number">0</span>), (<span class="number">2</span>, <span class="number">1</span>), (<span class="number">1</span>, <span class="number">3</span>)])</span><br><span class="line"><span class="keyword">assert</span> <span class="literal">False</span> == detect_cycle(<span class="number">4</span>, [(<span class="number">0</span>, <span class="number">1</span>), (<span class="number">2</span>, <span class="number">1</span>), (<span class="number">1</span>, <span class="number">3</span>)])</span><br></pre></td></tr></table></figure>
<h3 id="DFS"><a href="#DFS" class="headerlink" title="DFS"></a>DFS</h3><figure class="highlight python"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br><span class="line">19</span><br><span class="line">20</span><br><span class="line">21</span><br><span class="line">22</span><br><span class="line">23</span><br><span class="line">24</span><br><span class="line">25</span><br></pre></td><td class="code"><pre><span class="line"><span class="function"><span class="keyword">def</span> <span class="title">detect_cycle</span><span class="params">(n: int, edges: List[Tuple[int, int]])</span> -> bool:</span></span><br><span class="line"></span><br><span class="line"> <span class="function"><span class="keyword">def</span> <span class="title">dfs</span><span class="params">(u: int, p: int)</span> -> bool:</span></span><br><span class="line"> visited.add(u)</span><br><span class="line"></span><br><span class="line"> <span class="keyword">for</span> v <span class="keyword">in</span> graph[u]:</span><br><span class="line"> <span class="keyword">if</span> v == p: <span class="keyword">continue</span></span><br><span class="line"> <span class="keyword">if</span> v <span class="keyword">in</span> visited <span class="keyword">or</span> dfs(v, u):</span><br><span class="line"> <span class="keyword">return</span> <span class="literal">True</span></span><br><span class="line"></span><br><span class="line"> <span class="keyword">return</span> <span class="literal">False</span></span><br><span class="line"> </span><br><span class="line"> graph, visited = defaultdict(set), set()</span><br><span class="line"></span><br><span class="line"> <span class="keyword">for</span> u, v <span class="keyword">in</span> edges:</span><br><span class="line"> graph[u].add(v)</span><br><span class="line"> graph[v].add(u)</span><br><span class="line"></span><br><span class="line"> <span class="keyword">for</span> u <span class="keyword">in</span> range(n):</span><br><span class="line"> <span class="keyword">if</span> u <span class="keyword">not</span> <span class="keyword">in</span> visited <span class="keyword">and</span> dfs(u, <span class="literal">None</span>):</span><br><span class="line"> <span class="keyword">return</span> <span class="literal">True</span></span><br><span class="line"> <span class="keyword">return</span> <span class="literal">False</span></span><br><span class="line"></span><br><span class="line"><span class="keyword">assert</span> <span class="literal">True</span> == detect_cycle(<span class="number">4</span>, [(<span class="number">0</span>, <span class="number">2</span>), (<span class="number">1</span>, <span class="number">0</span>), (<span class="number">2</span>, <span class="number">1</span>), (<span class="number">1</span>, <span class="number">3</span>)])</span><br><span class="line"><span class="keyword">assert</span> <span class="literal">False</span> == detect_cycle(<span class="number">4</span>, [(<span class="number">0</span>, <span class="number">1</span>), (<span class="number">2</span>, <span class="number">1</span>), (<span class="number">1</span>, <span class="number">3</span>)])</span><br></pre></td></tr></table></figure>
<h2 id="Directed-Graph"><a href="#Directed-Graph" class="headerlink" title="Directed Graph"></a>Directed Graph</h2><h3 id="DFS-1"><a href="#DFS-1" class="headerlink" title="DFS"></a>DFS</h3><figure class="highlight python"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br><span class="line">19</span><br><span class="line">20</span><br><span class="line">21</span><br><span class="line">22</span><br><span class="line">23</span><br><span class="line">24</span><br></pre></td><td class="code"><pre><span class="line"><span class="function"><span class="keyword">def</span> <span class="title">detect_cycle</span><span class="params">(n: int, edges: List[Tuple[int, int]])</span> -> bool:</span></span><br><span class="line"></span><br><span class="line"> <span class="function"><span class="keyword">def</span> <span class="title">dfs</span><span class="params">(u: int)</span> -> bool:</span></span><br><span class="line"> visited.add(u), stack.add(u)</span><br><span class="line"></span><br><span class="line"> <span class="keyword">for</span> v <span class="keyword">in</span> graph[u]:</span><br><span class="line"> <span class="keyword">if</span> v <span class="keyword">in</span> stack <span class="keyword">or</span> v <span class="keyword">not</span> <span class="keyword">in</span> visited <span class="keyword">and</span> dfs(v):</span><br><span class="line"> <span class="keyword">return</span> <span class="literal">True</span></span><br><span class="line"></span><br><span class="line"> stack.remove(u)</span><br><span class="line"> <span class="keyword">return</span> <span class="literal">False</span></span><br><span class="line"> </span><br><span class="line"> graph, visited, stack = defaultdict(set), set(), set()</span><br><span class="line"></span><br><span class="line"> <span class="keyword">for</span> u, v <span class="keyword">in</span> edges:</span><br><span class="line"> graph[u].add(v)</span><br><span class="line"></span><br><span class="line"> <span class="keyword">for</span> u <span class="keyword">in</span> range(n):</span><br><span class="line"> <span class="keyword">if</span> u <span class="keyword">not</span> <span class="keyword">in</span> visited <span class="keyword">and</span> dfs(u):</span><br><span class="line"> <span class="keyword">return</span> <span class="literal">True</span></span><br><span class="line"> <span class="keyword">return</span> <span class="literal">False</span></span><br><span class="line"></span><br><span class="line"><span class="keyword">assert</span> <span class="literal">True</span> == detect_cycle(<span class="number">4</span>, [(<span class="number">0</span>, <span class="number">2</span>), (<span class="number">1</span>, <span class="number">0</span>), (<span class="number">2</span>, <span class="number">1</span>), (<span class="number">1</span>, <span class="number">3</span>)])</span><br><span class="line"><span class="keyword">assert</span> <span class="literal">False</span> == detect_cycle(<span class="number">4</span>, [(<span class="number">0</span>, <span class="number">2</span>), (<span class="number">0</span>, <span class="number">1</span>), (<span class="number">2</span>, <span class="number">1</span>), (<span class="number">1</span>, <span class="number">3</span>)])</span><br></pre></td></tr></table></figure>
<h1 id="Euler-Path"><a href="#Euler-Path" class="headerlink" title="Euler Path"></a>Euler Path</h1><figure class="highlight python"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br></pre></td><td class="code"><pre><span class="line"><span class="function"><span class="keyword">def</span> <span class="title">find_euler_path</span><span class="params">(start: int, edges: List[Tuple[int, int]])</span> -> List[int]:</span></span><br><span class="line"> <span class="comment"># Assume euler path does exist</span></span><br><span class="line"> <span class="function"><span class="keyword">def</span> <span class="title">dfs</span><span class="params">(u)</span>:</span></span><br><span class="line"> <span class="keyword">while</span> graph[u]:</span><br><span class="line"> v = graph[u].pop()</span><br><span class="line"> dfs(v)</span><br><span class="line"> ret.append(u)</span><br><span class="line"></span><br><span class="line"> graph, ret = defaultdict(set), []</span><br><span class="line"> <span class="keyword">for</span> u, v <span class="keyword">in</span> edges:</span><br><span class="line"> graph[u].add(v)</span><br><span class="line"> </span><br><span class="line"> dfs(start)</span><br><span class="line"> <span class="keyword">return</span> ret[::<span class="number">-1</span>]</span><br><span class="line"></span><br><span class="line">print(find_euler_path(<span class="number">0</span>, [(<span class="number">0</span>, <span class="number">1</span>), (<span class="number">1</span>, <span class="number">0</span>), (<span class="number">1</span>, <span class="number">2</span>), (<span class="number">2</span>, <span class="number">3</span>), (<span class="number">3</span>, <span class="number">1</span>), (<span class="number">1</span>, <span class="number">4</span>)] ))</span><br></pre></td></tr></table></figure>
<h1 id="Shortest-Path"><a href="#Shortest-Path" class="headerlink" title="Shortest Path"></a>Shortest Path</h1><h2 id="Dijkstra"><a href="#Dijkstra" class="headerlink" title="Dijkstra"></a>Dijkstra</h2><figure class="highlight python"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br><span class="line">19</span><br><span class="line">20</span><br><span class="line">21</span><br><span class="line">22</span><br><span class="line">23</span><br><span class="line">24</span><br><span class="line">25</span><br><span class="line">26</span><br><span class="line">27</span><br><span class="line">28</span><br></pre></td><td class="code"><pre><span class="line"><span class="keyword">from</span> sortedcontainers <span class="keyword">import</span> SortedList</span><br><span class="line"><span class="function"><span class="keyword">def</span> <span class="title">dijkstra</span><span class="params">(n: int, edges: List[Tuple[int, int, int]], begin: int, end: int)</span> -> List[int]:</span></span><br><span class="line"> graph, dist, prev = defaultdict(dict), defaultdict(<span class="keyword">lambda</span>: math.inf), {}</span><br><span class="line"></span><br><span class="line"> <span class="keyword">for</span> u, v, w <span class="keyword">in</span> edges:</span><br><span class="line"> graph[u][v] = w</span><br><span class="line"> </span><br><span class="line"> q = SortedList([(<span class="number">0</span>, begin)])</span><br><span class="line"> dist[begin] = <span class="number">0</span></span><br><span class="line"> <span class="keyword">while</span> q:</span><br><span class="line"> _, u = q.pop(<span class="number">0</span>)</span><br><span class="line"> <span class="keyword">for</span> v, w <span class="keyword">in</span> graph[u].items():</span><br><span class="line"> <span class="keyword">if</span> dist[v] > dist[u] + w:</span><br><span class="line"> q.discard((dist[v], v)) <span class="comment"># this will reduce the time complexity from O(E*log(V)) to O(V*log(V))</span></span><br><span class="line"> prev[v] = u</span><br><span class="line"> dist[v] = dist[u] + w</span><br><span class="line"> q.add((dist[v], v))</span><br><span class="line"></span><br><span class="line"> <span class="keyword">if</span> dist[end] == math.inf:</span><br><span class="line"> <span class="keyword">return</span> []</span><br><span class="line"></span><br><span class="line"> <span class="function"><span class="keyword">def</span> <span class="title">bt</span><span class="params">(cur)</span>:</span></span><br><span class="line"> <span class="keyword">if</span> cur == begin:</span><br><span class="line"> <span class="keyword">return</span> [begin]</span><br><span class="line"> <span class="keyword">return</span> bt(prev[cur]) + [cur]</span><br><span class="line"> <span class="keyword">return</span> bt(end)</span><br><span class="line"></span><br><span class="line">print(dijkstra(<span class="number">5</span>, [[<span class="number">0</span>, <span class="number">1</span>, <span class="number">2</span>], [<span class="number">0</span>, <span class="number">2</span>, <span class="number">5</span>], [<span class="number">1</span>, <span class="number">3</span>, <span class="number">3</span>], [<span class="number">2</span>, <span class="number">4</span>, <span class="number">10</span>], [<span class="number">3</span>, <span class="number">4</span>, <span class="number">3</span>]], <span class="number">0</span>, <span class="number">4</span>))</span><br></pre></td></tr></table></figure>
<h2 id="Bellman-Ford"><a href="#Bellman-Ford" class="headerlink" title="Bellman Ford"></a>Bellman Ford</h2><figure class="highlight python"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br><span class="line">19</span><br><span class="line">20</span><br><span class="line">21</span><br><span class="line">22</span><br><span class="line">23</span><br><span class="line">24</span><br><span class="line">25</span><br></pre></td><td class="code"><pre><span class="line"><span class="function"><span class="keyword">def</span> <span class="title">bellman_ford</span><span class="params">(n: int, edges: List[Tuple[int, int, int]], begin: int, end: int)</span> -> List[int]:</span></span><br><span class="line"> dist = defaultdict(<span class="keyword">lambda</span>: math.inf)</span><br><span class="line"> dist[begin], prev = <span class="number">0</span>, {}</span><br><span class="line"></span><br><span class="line"> <span class="keyword">for</span> _ <span class="keyword">in</span> range(n):</span><br><span class="line"> upd = <span class="number">0</span></span><br><span class="line"> <span class="keyword">for</span> u, v, w <span class="keyword">in</span> edges:</span><br><span class="line"> <span class="keyword">if</span> dist[v] > dist[u] + w:</span><br><span class="line"> dist[v] = dist[u] + w</span><br><span class="line"> prev[v] = u</span><br><span class="line"> upd += <span class="number">1</span></span><br><span class="line"> <span class="keyword">if</span> <span class="keyword">not</span> upd:</span><br><span class="line"> <span class="keyword">break</span></span><br><span class="line"> </span><br><span class="line"> <span class="keyword">for</span> u, v, w <span class="keyword">in</span> edges:</span><br><span class="line"> <span class="keyword">if</span> dist[u] + w < dist[v]:</span><br><span class="line"> <span class="keyword">raise</span> Exception(<span class="string">'Negative cycle'</span>)</span><br><span class="line"> </span><br><span class="line"> <span class="function"><span class="keyword">def</span> <span class="title">bt</span><span class="params">(u)</span>:</span></span><br><span class="line"> <span class="keyword">if</span> u == begin:</span><br><span class="line"> <span class="keyword">return</span> [begin]</span><br><span class="line"> <span class="keyword">return</span> bt(prev[u]) + [u]</span><br><span class="line"> <span class="keyword">return</span> bt(end)</span><br><span class="line"></span><br><span class="line">print(bellman_ford(<span class="number">5</span>, [[<span class="number">0</span>, <span class="number">1</span>, <span class="number">2</span>], [<span class="number">0</span>, <span class="number">2</span>, <span class="number">5</span>], [<span class="number">1</span>, <span class="number">3</span>, <span class="number">3</span>], [<span class="number">2</span>, <span class="number">4</span>, <span class="number">10</span>], [<span class="number">3</span>, <span class="number">4</span>, <span class="number">3</span>]], <span class="number">0</span>, <span class="number">4</span>))</span><br></pre></td></tr></table></figure>
<h2 id="Floyd-Warshall"><a href="#Floyd-Warshall" class="headerlink" title="Floyd Warshall"></a>Floyd Warshall</h2><figure class="highlight python"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br></pre></td><td class="code"><pre><span class="line"><span class="function"><span class="keyword">def</span> <span class="title">floyd_warshall</span><span class="params">(n: int, edges: List[Tuple[int, int, int]], begin: int, end: int)</span> -> int:</span></span><br><span class="line"> dist = defaultdict(<span class="keyword">lambda</span>: math.inf)</span><br><span class="line"></span><br><span class="line"> <span class="keyword">for</span> u, v, w <span class="keyword">in</span> edges:</span><br><span class="line"> dist[(u, v)] = w</span><br><span class="line"> </span><br><span class="line"> <span class="keyword">for</span> k <span class="keyword">in</span> range(n):</span><br><span class="line"> <span class="keyword">for</span> u <span class="keyword">in</span> range(n):</span><br><span class="line"> <span class="keyword">for</span> v <span class="keyword">in</span> range(n):</span><br><span class="line"> <span class="keyword">if</span> dist[(u, k)] + dist[(k, v)] < dist[(u, v)]:</span><br><span class="line"> dist[(u, v)] = dist[(u, k)] + dist[(k, v)]</span><br><span class="line"> </span><br><span class="line"> <span class="keyword">return</span> dist[(begin, end)]</span><br><span class="line"></span><br><span class="line">print(floyd_warshall(<span class="number">5</span>, [[<span class="number">0</span>, <span class="number">1</span>, <span class="number">2</span>], [<span class="number">0</span>, <span class="number">2</span>, <span class="number">5</span>], [<span class="number">1</span>, <span class="number">3</span>, <span class="number">3</span>], [<span class="number">2</span>, <span class="number">4</span>, <span class="number">10</span>], [<span class="number">3</span>, <span class="number">4</span>, <span class="number">3</span>]], <span class="number">0</span>, <span class="number">4</span>))</span><br></pre></td></tr></table></figure>
<h1 id="Minimal-Spanning-Tree"><a href="#Minimal-Spanning-Tree" class="headerlink" title="Minimal Spanning Tree"></a>Minimal Spanning Tree</h1><h2 id="Kruskal’s-method"><a href="#Kruskal’s-method" class="headerlink" title="Kruskal’s method"></a>Kruskal’s method</h2><figure class="highlight python"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br></pre></td><td class="code"><pre><span class="line"><span class="function"><span class="keyword">def</span> <span class="title">kruskal</span><span class="params">(n: int, edges: List[Tuple[int, int, int]])</span> -> int:</span></span><br><span class="line"> uf, ret = UF(), []</span><br><span class="line"></span><br><span class="line"> <span class="keyword">for</span> u, v, w <span class="keyword">in</span> sorted(edges, key=<span class="keyword">lambda</span> x: x[<span class="number">2</span>]):</span><br><span class="line"> <span class="keyword">if</span> uf.find(u) != uf.find(v):</span><br><span class="line"> ret.append((u, v, w))</span><br><span class="line"> uf.union(u, v)</span><br><span class="line"> </span><br><span class="line"> <span class="keyword">return</span> ret <span class="keyword">if</span> len(set(map(uf.find, range(n)))) == <span class="number">1</span> <span class="keyword">else</span> []</span><br><span class="line"></span><br><span class="line">print(kruskal(<span class="number">5</span>, [[<span class="number">0</span>, <span class="number">1</span>, <span class="number">2</span>], [<span class="number">0</span>, <span class="number">2</span>, <span class="number">5</span>], [<span class="number">1</span>, <span class="number">3</span>, <span class="number">3</span>], [<span class="number">2</span>, <span class="number">4</span>, <span class="number">10</span>], [<span class="number">3</span>, <span class="number">4</span>, <span class="number">3</span>]]))</span><br></pre></td></tr></table></figure>
<h2 id="Prim’s-method"><a href="#Prim’s-method" class="headerlink" title="Prim’s method"></a>Prim’s method</h2><figure class="highlight python"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br><span class="line">19</span><br><span class="line">20</span><br><span class="line">21</span><br><span class="line">22</span><br><span class="line">23</span><br><span class="line">24</span><br><span class="line">25</span><br><span class="line">26</span><br><span class="line">27</span><br></pre></td><td class="code"><pre><span class="line"><span class="keyword">from</span> sortedcontainers <span class="keyword">import</span> SortedList</span><br><span class="line"><span class="function"><span class="keyword">def</span> <span class="title">prim</span><span class="params">(n: int, edges: List[Tuple[int, int, int]])</span> -> int:</span></span><br><span class="line"> graph = defaultdict(dict)</span><br><span class="line"> <span class="keyword">for</span> u, v, w <span class="keyword">in</span> edges:</span><br><span class="line"> graph[u][v] = w</span><br><span class="line"> </span><br><span class="line"> start = <span class="number">0</span></span><br><span class="line"> pq, ret, visited, prev = SortedList([(<span class="number">0</span>, start, <span class="literal">None</span>)]), [], set(), {}</span><br><span class="line"></span><br><span class="line"> <span class="keyword">while</span> pq:</span><br><span class="line"> <span class="keyword">if</span> len(visited) == n:</span><br><span class="line"> <span class="keyword">break</span></span><br><span class="line"> w, u, p = pq.pop(<span class="number">0</span>)</span><br><span class="line"> <span class="keyword">if</span> u <span class="keyword">in</span> visited: <span class="keyword">continue</span></span><br><span class="line"></span><br><span class="line"> visited.add(u), ret.append((p, u, w))</span><br><span class="line"></span><br><span class="line"> <span class="keyword">for</span> v, w <span class="keyword">in</span> graph[u].items():</span><br><span class="line"> <span class="keyword">if</span> v <span class="keyword">in</span> visited: <span class="keyword">continue</span></span><br><span class="line"> <span class="keyword">if</span> v <span class="keyword">in</span> prev <span class="keyword">and</span> prev[v][<span class="number">1</span>] >= w:</span><br><span class="line"> pq.remove((prev[v][<span class="number">1</span>], v, prev[v][<span class="number">0</span>]))</span><br><span class="line"> prev[v] = (u, w)</span><br><span class="line"> pq.add((w, v, u))</span><br><span class="line"> </span><br><span class="line"> <span class="keyword">return</span> ret[<span class="number">1</span>:] <span class="keyword">if</span> len(visited) == n <span class="keyword">else</span> []</span><br><span class="line"> </span><br><span class="line">print(prim(<span class="number">5</span>, [[<span class="number">0</span>, <span class="number">1</span>, <span class="number">2</span>], [<span class="number">0</span>, <span class="number">2</span>, <span class="number">5</span>], [<span class="number">1</span>, <span class="number">3</span>, <span class="number">3</span>], [<span class="number">2</span>, <span class="number">4</span>, <span class="number">10</span>], [<span class="number">3</span>, <span class="number">4</span>, <span class="number">3</span>]]))</span><br></pre></td></tr></table></figure>
<h1 id="Tarjan’s-algorithm"><a href="#Tarjan’s-algorithm" class="headerlink" title="Tarjan’s algorithm"></a>Tarjan’s algorithm</h1><h2 id="Strong-Connected-Component"><a href="#Strong-Connected-Component" class="headerlink" title="Strong Connected Component"></a>Strong Connected Component</h2><h2 id="Cutting-Edge"><a href="#Cutting-Edge" class="headerlink" title="Cutting Edge"></a>Cutting Edge</h2><h2 id="Cutting-Vertex"><a href="#Cutting-Vertex" class="headerlink" title="Cutting Vertex"></a>Cutting Vertex</h2>
</div>
<footer class="post-footer">
<div class="post-eof"></div>
</footer>
</article>
<article itemscope itemtype="http://schema.org/Article" class="post-block" lang="en">
<link itemprop="mainEntityOfPage" href="http://yonglife.com/2020/09/20/weekly-contest-207/">
<span hidden itemprop="author" itemscope itemtype="http://schema.org/Person">
<meta itemprop="image" content="/images/headImage.jpg">
<meta itemprop="name" content="Yong Cao">
<meta itemprop="description" content="Record . Grow . Evolve">
</span>
<span hidden itemprop="publisher" itemscope itemtype="http://schema.org/Organization">
<meta itemprop="name" content="Yong's Blog">
</span>
<header class="post-header">
<h2 class="post-title" itemprop="name headline">
<a href="/2020/09/20/weekly-contest-207/" class="post-title-link" itemprop="url">Weekly Contest 207</a>
</h2>
<div class="post-meta">
<span class="post-meta-item">
<span class="post-meta-item-icon">
<i class="far fa-calendar"></i>
</span>
<span class="post-meta-item-text">Posted on</span>
<time title="Created: 2020-09-20 12:38:28 / Modified: 10:32:22" itemprop="dateCreated datePublished" datetime="2020-09-20T12:38:28-07:00">2020-09-20</time>
</span>
<span class="post-meta-item">
<span class="post-meta-item-icon">
<i class="far fa-folder"></i>
</span>
<span class="post-meta-item-text">In</span>
<span itemprop="about" itemscope itemtype="http://schema.org/Thing">
<a href="/categories/Program/" itemprop="url" rel="index"><span itemprop="name">Program</span></a>
</span>
</span>
<span id="/2020/09/20/weekly-contest-207/" class="post-meta-item leancloud_visitors" data-flag-title="Weekly Contest 207" title="Views">
<span class="post-meta-item-icon">
<i class="fa fa-eye"></i>
</span>
<span class="post-meta-item-text">Views: </span>
<span class="leancloud-visitors-count"></span>
</span>
<span class="post-meta-item">
<span class="post-meta-item-icon">
<i class="far fa-comment"></i>
</span>
<span class="post-meta-item-text">Valine: </span>
<a title="valine" href="/2020/09/20/weekly-contest-207/#valine-comments" itemprop="discussionUrl">
<span class="post-comments-count valine-comment-count" data-xid="/2020/09/20/weekly-contest-207/" itemprop="commentCount"></span>
</a>
</span>
</div>
</header>
<div class="post-body" itemprop="articleBody">
<h1 id="Q1-1592-Rearrange-Spaces-Between-Words"><a href="#Q1-1592-Rearrange-Spaces-Between-Words" class="headerlink" title="Q1. 1592. Rearrange Spaces Between Words"></a>Q1. <a href="https://leetcode.com/problems/rearrange-spaces-between-words/" target="_blank" rel="noopener">1592. Rearrange Spaces Between Words</a></h1><figure class="highlight python"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br></pre></td><td class="code"><pre><span class="line"><span class="class"><span class="keyword">class</span> <span class="title">Solution</span>:</span></span><br><span class="line"> <span class="function"><span class="keyword">def</span> <span class="title">reorderSpaces</span><span class="params">(self, text: str)</span> -> str:</span></span><br><span class="line"> words = text.split()</span><br><span class="line"> spaces, n = text.count(<span class="string">' '</span>), len(words)</span><br><span class="line"> ret = <span class="string">''</span></span><br><span class="line"> </span><br><span class="line"> <span class="keyword">for</span> i, word <span class="keyword">in</span> enumerate(words):</span><br><span class="line"> ret += word</span><br><span class="line"> <span class="keyword">if</span> n > <span class="number">1</span> <span class="keyword">and</span> i != n<span class="number">-1</span>:</span><br><span class="line"> ret += <span class="string">' '</span> * (spaces // (n<span class="number">-1</span>))</span><br><span class="line"></span><br><span class="line"> <span class="keyword">return</span> ret + <span class="string">' '</span> * ((spaces % (n<span class="number">-1</span>)) <span class="keyword">if</span> n><span class="number">1</span> <span class="keyword">else</span> spaces)</span><br></pre></td></tr></table></figure>
<!--noindex-->
<div class="post-button">
<a class="btn" href="/2020/09/20/weekly-contest-207/#more" rel="contents">
Read more »
</a>
</div>
<!--/noindex-->
</div>
<footer class="post-footer">
<div class="post-eof"></div>
</footer>
</article>
<article itemscope itemtype="http://schema.org/Article" class="post-block" lang="en">
<link itemprop="mainEntityOfPage" href="http://yonglife.com/2020/09/20/Fraction/">
<span hidden itemprop="author" itemscope itemtype="http://schema.org/Person">
<meta itemprop="image" content="/images/headImage.jpg">
<meta itemprop="name" content="Yong Cao">
<meta itemprop="description" content="Record . Grow . Evolve">
</span>
<span hidden itemprop="publisher" itemscope itemtype="http://schema.org/Organization">
<meta itemprop="name" content="Yong's Blog">
</span>
<header class="post-header">
<h2 class="post-title" itemprop="name headline">
<a href="/2020/09/20/Fraction/" class="post-title-link" itemprop="url">Fraction</a>
</h2>
<div class="post-meta">
<span class="post-meta-item">
<span class="post-meta-item-icon">
<i class="far fa-calendar"></i>
</span>
<span class="post-meta-item-text">Posted on</span>
<time title="Created: 2020-09-20 12:30:08 / Modified: 09:33:07" itemprop="dateCreated datePublished" datetime="2020-09-20T12:30:08-07:00">2020-09-20</time>
</span>
<span class="post-meta-item">
<span class="post-meta-item-icon">
<i class="far fa-folder"></i>
</span>
<span class="post-meta-item-text">In</span>
<span itemprop="about" itemscope itemtype="http://schema.org/Thing">
<a href="/categories/Program/" itemprop="url" rel="index"><span itemprop="name">Program</span></a>
</span>
</span>
<span id="/2020/09/20/Fraction/" class="post-meta-item leancloud_visitors" data-flag-title="Fraction" title="Views">
<span class="post-meta-item-icon">
<i class="fa fa-eye"></i>
</span>
<span class="post-meta-item-text">Views: </span>
<span class="leancloud-visitors-count"></span>
</span>
<span class="post-meta-item">
<span class="post-meta-item-icon">
<i class="far fa-comment"></i>
</span>
<span class="post-meta-item-text">Valine: </span>
<a title="valine" href="/2020/09/20/Fraction/#valine-comments" itemprop="discussionUrl">
<span class="post-comments-count valine-comment-count" data-xid="/2020/09/20/Fraction/" itemprop="commentCount"></span>
</a>
</span>
</div>
</header>
<div class="post-body" itemprop="articleBody">
<figure class="highlight python"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br><span class="line">19</span><br><span class="line">20</span><br><span class="line">21</span><br></pre></td><td class="code"><pre><span class="line"><span class="class"><span class="keyword">class</span> <span class="title">Fraction</span>:</span></span><br><span class="line"> <span class="function"><span class="keyword">def</span> <span class="title">__init__</span><span class="params">(self, numerator: int, denominator: int)</span>:</span></span><br><span class="line"> self.numerator = numerator</span><br><span class="line"> self.denominator = denominator</span><br><span class="line"> </span><br><span class="line"> <span class="function"><span class="keyword">def</span> <span class="title">__str__</span><span class="params">(self)</span>:</span></span><br><span class="line"> <span class="keyword">return</span> <span class="string">f'<span class="subst">{self.numerator}</span> / <span class="subst">{self.denominator}</span>'</span></span><br><span class="line"></span><br><span class="line"> <span class="function"><span class="keyword">def</span> <span class="title">__lt__</span><span class="params">(self, rhs: Fraction)</span>:</span></span><br><span class="line"> l, r = self.numerator * rhs.denominator, self.denominator * rhs.numerator</span><br><span class="line"> <span class="keyword">return</span> l < r</span><br><span class="line"> </span><br><span class="line"> <span class="function"><span class="keyword">def</span> <span class="title">__add__</span><span class="params">(self, rhs: Fraction)</span>:</span></span><br><span class="line"> numerator, denominator = self.numerator * rhs.denominator + rhs.numerator * self.denominator, \</span><br><span class="line"> self.denominator * rhs.denominator</span><br><span class="line"> gcd_val = math.gcd(numerator, denominator)</span><br><span class="line"> <span class="keyword">return</span> Fraction(numerator // gcd_val, denominator // gcd_val)</span><br><span class="line"> </span><br><span class="line"> <span class="function"><span class="keyword">def</span> <span class="title">__sub__</span><span class="params">(self, rhs: Fraction)</span>:</span></span><br><span class="line"> numerator, denominator = rhs.numerator, rhs.denominator</span><br><span class="line"> <span class="keyword">return</span> self.__add__(Fraction(-numerator, denominator))</span><br></pre></td></tr></table></figure>
</div>
<footer class="post-footer">
<div class="post-eof"></div>
</footer>
</article>
<article itemscope itemtype="http://schema.org/Article" class="post-block" lang="en">
<link itemprop="mainEntityOfPage" href="http://yonglife.com/2020/08/23/Top-K-out-of-N-numbers/">
<span hidden itemprop="author" itemscope itemtype="http://schema.org/Person">
<meta itemprop="image" content="/images/headImage.jpg">
<meta itemprop="name" content="Yong Cao">
<meta itemprop="description" content="Record . Grow . Evolve">
</span>
<span hidden itemprop="publisher" itemscope itemtype="http://schema.org/Organization">
<meta itemprop="name" content="Yong's Blog">
</span>
<header class="post-header">
<h2 class="post-title" itemprop="name headline">
<a href="/2020/08/23/Top-K-out-of-N-numbers/" class="post-title-link" itemprop="url">Top K out of N numbers</a>
</h2>
<div class="post-meta">
<span class="post-meta-item">
<span class="post-meta-item-icon">
<i class="far fa-calendar"></i>
</span>
<span class="post-meta-item-text">Posted on</span>
<time title="Created: 2020-08-23 20:24:13 / Modified: 18:11:09" itemprop="dateCreated datePublished" datetime="2020-08-23T20:24:13-07:00">2020-08-23</time>
</span>
<span class="post-meta-item">
<span class="post-meta-item-icon">
<i class="far fa-folder"></i>
</span>
<span class="post-meta-item-text">In</span>
<span itemprop="about" itemscope itemtype="http://schema.org/Thing">
<a href="/categories/Program/" itemprop="url" rel="index"><span itemprop="name">Program</span></a>
</span>
</span>
<span id="/2020/08/23/Top-K-out-of-N-numbers/" class="post-meta-item leancloud_visitors" data-flag-title="Top K out of N numbers" title="Views">
<span class="post-meta-item-icon">
<i class="fa fa-eye"></i>
</span>
<span class="post-meta-item-text">Views: </span>
<span class="leancloud-visitors-count"></span>
</span>
<span class="post-meta-item">
<span class="post-meta-item-icon">
<i class="far fa-comment"></i>
</span>
<span class="post-meta-item-text">Valine: </span>
<a title="valine" href="/2020/08/23/Top-K-out-of-N-numbers/#valine-comments" itemprop="discussionUrl">
<span class="post-comments-count valine-comment-count" data-xid="/2020/08/23/Top-K-out-of-N-numbers/" itemprop="commentCount"></span>
</a>
</span>
</div>
</header>
<div class="post-body" itemprop="articleBody">
<h1 id="Prerequisite"><a href="#Prerequisite" class="headerlink" title="Prerequisite"></a>Prerequisite</h1><ol>
<li><a href="https://en.wikipedia.org/wiki/Binary_heap" target="_blank" rel="noopener">What is a binary-heap</a></li>
<li>It takes O(N) to heapify an array contains N integer</li>
</ol>
<h1 id="N-Log-K"><a href="#N-Log-K" class="headerlink" title="N*Log(K)"></a>N*Log(K)</h1><figure class="highlight python"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br></pre></td><td class="code"><pre><span class="line"><span class="function"><span class="keyword">def</span> <span class="title">get_k_smallest</span><span class="params">(k: int, arr: List[int])</span>:</span></span><br><span class="line"> heap = []</span><br><span class="line"> <span class="keyword">for</span> num <span class="keyword">in</span> arr:</span><br><span class="line"> heapq.heappush(heap, -num) <span class="comment"># we push -num as we want to build a max-heap</span></span><br><span class="line"> <span class="keyword">if</span> len(heap) > k:</span><br><span class="line"> heapq.heappop(heap)</span><br><span class="line"> <span class="keyword">return</span> [-num <span class="keyword">for</span> num <span class="keyword">in</span> heap]</span><br></pre></td></tr></table></figure>
<h1 id="K-Log-N"><a href="#K-Log-N" class="headerlink" title="K*Log(N)"></a>K*Log(N)</h1><figure class="highlight python"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br></pre></td><td class="code"><pre><span class="line"><span class="function"><span class="keyword">def</span> <span class="title">get_k_smallest</span><span class="params">(k: int, arr: List[int])</span>:</span></span><br><span class="line"> heapq.heapify(arr)</span><br><span class="line"> <span class="keyword">return</span> [heapq.heappop(arr) <span class="keyword">for</span> i <span class="keyword">in</span> range(k)]</span><br></pre></td></tr></table></figure>
<h1 id="K-Log-K"><a href="#K-Log-K" class="headerlink" title="K*Log(K)"></a>K*Log(K)</h1><figure class="highlight python"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br></pre></td><td class="code"><pre><span class="line"><span class="function"><span class="keyword">def</span> <span class="title">get_k_smallest</span><span class="params">(k: int, arr: List[int])</span>:</span></span><br><span class="line"> heapq.heapify(arr)</span><br><span class="line"> heap = [(arr[<span class="number">0</span>], <span class="number">0</span>)]</span><br><span class="line"> ret = []</span><br><span class="line"> <span class="keyword">for</span> _ <span class="keyword">in</span> range(k):</span><br><span class="line"> num, idx = heapq.heappop(heap)</span><br><span class="line"> ret.append(num)</span><br><span class="line"> heapq.heappush(heap, (arr[idx*<span class="number">2</span>+<span class="number">1</span>], idx*<span class="number">2</span>+<span class="number">1</span>))</span><br><span class="line"> heapq.heappush(heap, (arr[idx*<span class="number">2</span>+<span class="number">2</span>], idx*<span class="number">2</span>+<span class="number">2</span>))</span><br><span class="line"> <span class="keyword">return</span> ret</span><br></pre></td></tr></table></figure>
<h1 id="Test"><a href="#Test" class="headerlink" title="Test"></a>Test</h1><figure class="highlight python"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br><span class="line">19</span><br><span class="line">20</span><br><span class="line">21</span><br><span class="line">22</span><br><span class="line">23</span><br><span class="line">24</span><br><span class="line">25</span><br><span class="line">26</span><br><span class="line">27</span><br><span class="line">28</span><br><span class="line">29</span><br><span class="line">30</span><br><span class="line">31</span><br><span class="line">32</span><br><span class="line">33</span><br><span class="line">34</span><br><span class="line">35</span><br><span class="line">36</span><br><span class="line">37</span><br><span class="line">38</span><br><span class="line">39</span><br><span class="line">40</span><br><span class="line">41</span><br><span class="line">42</span><br><span class="line">43</span><br><span class="line">44</span><br><span class="line">45</span><br><span class="line">46</span><br><span class="line">47</span><br><span class="line">48</span><br><span class="line">49</span><br><span class="line">50</span><br><span class="line">51</span><br><span class="line">52</span><br><span class="line">53</span><br><span class="line">54</span><br><span class="line">55</span><br><span class="line">56</span><br><span class="line">57</span><br><span class="line">58</span><br><span class="line">59</span><br><span class="line">60</span><br><span class="line">61</span><br><span class="line">62</span><br><span class="line">63</span><br><span class="line">64</span><br></pre></td><td class="code"><pre><span class="line"><span class="keyword">import</span> heapq</span><br><span class="line"><span class="keyword">import</span> timeit</span><br><span class="line"></span><br><span class="line"></span><br><span class="line"><span class="function"><span class="keyword">def</span> <span class="title">timer</span><span class="params">(function)</span>:</span></span><br><span class="line"> <span class="function"><span class="keyword">def</span> <span class="title">new_function</span><span class="params">(*args, **kw)</span>:</span></span><br><span class="line"> start_time = timeit.default_timer()</span><br><span class="line"> ret = function(*args, **kw)</span><br><span class="line"> elapsed = timeit.default_timer() - start_time</span><br><span class="line"> print(<span class="string">'Function "{name}" took {time} seconds to complete.'</span>.format(name=function.__name__, time=elapsed))</span><br><span class="line"> <span class="keyword">return</span> ret</span><br><span class="line"> <span class="keyword">return</span> new_function</span><br><span class="line"></span><br><span class="line"><span class="meta">@timer</span></span><br><span class="line"><span class="function"><span class="keyword">def</span> <span class="title">addition</span><span class="params">()</span>:</span></span><br><span class="line"> total = <span class="number">0</span></span><br><span class="line"> <span class="keyword">for</span> i <span class="keyword">in</span> range(<span class="number">0</span>,<span class="number">1000000</span>):</span><br><span class="line"> total += i</span><br><span class="line"> <span class="keyword">return</span> total</span><br><span class="line"></span><br><span class="line"></span><br><span class="line"></span><br><span class="line"><span class="meta">@timer</span></span><br><span class="line"><span class="function"><span class="keyword">def</span> <span class="title">get_k_smallest1</span><span class="params">(k: int, arr: List[int])</span>:</span></span><br><span class="line"> heap = []</span><br><span class="line"> <span class="keyword">for</span> num <span class="keyword">in</span> arr:</span><br><span class="line"> heapq.heappush(heap, -num) <span class="comment"># we push -num as we want to build a max-heap</span></span><br><span class="line"> <span class="keyword">if</span> len(heap) > k:</span><br><span class="line"> heapq.heappop(heap)</span><br><span class="line"> <span class="keyword">return</span> [-num <span class="keyword">for</span> num <span class="keyword">in</span> heap]</span><br><span class="line"></span><br><span class="line"></span><br><span class="line"><span class="meta">@timer</span></span><br><span class="line"><span class="function"><span class="keyword">def</span> <span class="title">get_k_smallest2</span><span class="params">(k: int, arr: List[int])</span>:</span></span><br><span class="line"> heapq.heapify(arr)</span><br><span class="line"> <span class="keyword">return</span> [heapq.heappop(arr) <span class="keyword">for</span> i <span class="keyword">in</span> range(k)]</span><br><span class="line"></span><br><span class="line"></span><br><span class="line"><span class="meta">@timer</span></span><br><span class="line"><span class="function"><span class="keyword">def</span> <span class="title">get_k_smallest3</span><span class="params">(k: int, arr: List[int])</span>:</span></span><br><span class="line"> heapq.heapify(arr)</span><br><span class="line"> heap = [(arr[<span class="number">0</span>], <span class="number">0</span>)]</span><br><span class="line"> ret = []</span><br><span class="line"> <span class="keyword">for</span> _ <span class="keyword">in</span> range(k):</span><br><span class="line"> num, idx = heapq.heappop(heap)</span><br><span class="line"> ret.append(num)</span><br><span class="line"> heapq.heappush(heap, (arr[idx*<span class="number">2</span>+<span class="number">1</span>], idx*<span class="number">2</span>+<span class="number">1</span>))</span><br><span class="line"> heapq.heappush(heap, (arr[idx*<span class="number">2</span>+<span class="number">2</span>], idx*<span class="number">2</span>+<span class="number">2</span>))</span><br><span class="line"> <span class="keyword">return</span> ret</span><br><span class="line"></span><br><span class="line">k = <span class="number">5</span></span><br><span class="line">arr = [randrange(<span class="number">0</span>, <span class="number">100000000</span>) <span class="keyword">for</span> i <span class="keyword">in</span> range(<span class="number">10000000</span>)]</span><br><span class="line"></span><br><span class="line">ans = set(sorted(arr)[:k])</span><br><span class="line"><span class="keyword">assert</span> ans == set(get_k_smallest1(k, list(arr)))</span><br><span class="line"><span class="keyword">assert</span> ans == set(get_k_smallest2(k, list(arr)))</span><br><span class="line"><span class="keyword">assert</span> ans == set(get_k_smallest3(k, list(arr)))</span><br><span class="line"></span><br><span class="line"><span class="string">'''</span></span><br><span class="line"><span class="string">» /usr/local/opt/[email protected]/bin/python3.8 /Users/yongcao/Program/tmp/py.py yongs-MBP</span></span><br><span class="line"><span class="string">Function "get_k_smallest1" took 3.168419736999999 seconds to complete.</span></span><br><span class="line"><span class="string">Function "get_k_smallest2" took 0.3814774750000005 seconds to complete.</span></span><br><span class="line"><span class="string">Function "get_k_smallest3" took 0.37742361599999974 seconds to complete.</span></span><br><span class="line"><span class="string">'''</span></span><br></pre></td></tr></table></figure>
</div>
<footer class="post-footer">
<div class="post-eof"></div>
</footer>
</article>
<article itemscope itemtype="http://schema.org/Article" class="post-block" lang="en">
<link itemprop="mainEntityOfPage" href="http://yonglife.com/2020/08/23/Tarjan-s-algorithm/">
<span hidden itemprop="author" itemscope itemtype="http://schema.org/Person">
<meta itemprop="image" content="/images/headImage.jpg">
<meta itemprop="name" content="Yong Cao">
<meta itemprop="description" content="Record . Grow . Evolve">
</span>
<span hidden itemprop="publisher" itemscope itemtype="http://schema.org/Organization">
<meta itemprop="name" content="Yong's Blog">
</span>
<header class="post-header">
<h2 class="post-title" itemprop="name headline">
<a href="/2020/08/23/Tarjan-s-algorithm/" class="post-title-link" itemprop="url">Tarjan's algorithm</a>
</h2>
<div class="post-meta">
<span class="post-meta-item">
<span class="post-meta-item-icon">
<i class="far fa-calendar"></i>
</span>
<span class="post-meta-item-text">Posted on</span>
<time title="Created: 2020-08-23 13:00:07" itemprop="dateCreated datePublished" datetime="2020-08-23T13:00:07-07:00">2020-08-23</time>
</span>
<span class="post-meta-item">
<span class="post-meta-item-icon">
<i class="far fa-calendar-check"></i>
</span>
<span class="post-meta-item-text">Edited on</span>
<time title="Modified: 2020-09-28 19:53:19" itemprop="dateModified" datetime="2020-09-28T19:53:19-07:00">2020-09-28</time>
</span>
<span class="post-meta-item">
<span class="post-meta-item-icon">
<i class="far fa-folder"></i>
</span>
<span class="post-meta-item-text">In</span>
<span itemprop="about" itemscope itemtype="http://schema.org/Thing">
<a href="/categories/Program/" itemprop="url" rel="index"><span itemprop="name">Program</span></a>
</span>
</span>
<span id="/2020/08/23/Tarjan-s-algorithm/" class="post-meta-item leancloud_visitors" data-flag-title="Tarjan's algorithm" title="Views">
<span class="post-meta-item-icon">
<i class="fa fa-eye"></i>
</span>
<span class="post-meta-item-text">Views: </span>
<span class="leancloud-visitors-count"></span>
</span>
<span class="post-meta-item">
<span class="post-meta-item-icon">
<i class="far fa-comment"></i>
</span>
<span class="post-meta-item-text">Valine: </span>
<a title="valine" href="/2020/08/23/Tarjan-s-algorithm/#valine-comments" itemprop="discussionUrl">
<span class="post-comments-count valine-comment-count" data-xid="/2020/08/23/Tarjan-s-algorithm/" itemprop="commentCount"></span>
</a>
</span>
</div>
</header>
<div class="post-body" itemprop="articleBody">
<h1 id="Find-Strong-Connected-Components-SCC"><a href="#Find-Strong-Connected-Components-SCC" class="headerlink" title="Find Strong Connected Components (SCC)"></a>Find Strong Connected Components (SCC)</h1><p><a href="https://www.youtube.com/watch?v=wUgWX0nc4NY" target="_blank" rel="noopener">Video</a></p>
<figure class="highlight python"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br><span class="line">19</span><br><span class="line">20</span><br><span class="line">21</span><br><span class="line">22</span><br><span class="line">23</span><br><span class="line">24</span><br><span class="line">25</span><br><span class="line">26</span><br><span class="line">27</span><br><span class="line">28</span><br><span class="line">29</span><br><span class="line">30</span><br><span class="line">31</span><br><span class="line">32</span><br></pre></td><td class="code"><pre><span class="line"><span class="function"><span class="keyword">def</span> <span class="title">find_scc</span><span class="params">(n: int, edges: List[List[int]])</span>:</span></span><br><span class="line"> graph = defaultdict(set)</span><br><span class="line"> <span class="keyword">for</span> u, v <span class="keyword">in</span> edges:</span><br><span class="line"> graph[u].add(v)</span><br><span class="line"> graph[v].add(u)</span><br><span class="line"></span><br><span class="line"> ids, low = [<span class="number">-1</span>] * n, [<span class="number">-1</span>] * n</span><br><span class="line"> stack, in_stack = [], [<span class="literal">False</span>] * n</span><br><span class="line"> id_max = <span class="number">0</span></span><br><span class="line"></span><br><span class="line"> <span class="function"><span class="keyword">def</span> <span class="title">dfs</span><span class="params">(u)</span>:</span></span><br><span class="line"> <span class="keyword">nonlocal</span> id_max</span><br><span class="line"> stack.append(u)</span><br><span class="line"> in_stack[u] = <span class="literal">True</span></span><br><span class="line"> ids[u] = low[u] = id_max</span><br><span class="line"> id_max += <span class="number">1</span></span><br><span class="line"></span><br><span class="line"> <span class="keyword">for</span> v <span class="keyword">in</span> graph[u]:</span><br><span class="line"> <span class="keyword">if</span> ids[v] == <span class="number">-1</span>: dfs(v)</span><br><span class="line"> <span class="keyword">if</span> in_stack[v]:</span><br><span class="line"> low[u] = min(low[u], low[v])</span><br><span class="line"> </span><br><span class="line"> <span class="keyword">if</span> low[u] == ids[u]:</span><br><span class="line"> <span class="keyword">while</span> <span class="literal">True</span>:</span><br><span class="line"> node = stack.pop()</span><br><span class="line"> in_stack[node] = <span class="literal">False</span></span><br><span class="line"> <span class="keyword">if</span> node == u: <span class="keyword">break</span></span><br><span class="line"> </span><br><span class="line"> <span class="keyword">for</span> i <span class="keyword">in</span> range(n):</span><br><span class="line"> <span class="keyword">if</span> ids[i] == <span class="number">-1</span>:</span><br><span class="line"> dfs(i)</span><br><span class="line"> <span class="keyword">return</span> low</span><br></pre></td></tr></table></figure>
<!--noindex-->
<div class="post-button">
<a class="btn" href="/2020/08/23/Tarjan-s-algorithm/#more" rel="contents">
Read more »
</a>
</div>
<!--/noindex-->
</div>
<footer class="post-footer">
<div class="post-eof"></div>
</footer>
</article>
<article itemscope itemtype="http://schema.org/Article" class="post-block" lang="en">
<link itemprop="mainEntityOfPage" href="http://yonglife.com/2020/08/22/Detect-Cycle-in-a-Graph/">
<span hidden itemprop="author" itemscope itemtype="http://schema.org/Person">
<meta itemprop="image" content="/images/headImage.jpg">
<meta itemprop="name" content="Yong Cao">
<meta itemprop="description" content="Record . Grow . Evolve">
</span>
<span hidden itemprop="publisher" itemscope itemtype="http://schema.org/Organization">
<meta itemprop="name" content="Yong's Blog">
</span>
<header class="post-header">
<h2 class="post-title" itemprop="name headline">
<a href="/2020/08/22/Detect-Cycle-in-a-Graph/" class="post-title-link" itemprop="url">Detect Cycle in a Graph</a>
</h2>
<div class="post-meta">
<span class="post-meta-item">