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youngyangyang04 committed Apr 26, 2021
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51 changes: 24 additions & 27 deletions README.md
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1. [数组过于简单，但你该了解这些！](./problems/数组理论基础.md)
2. [数组：每次遇到二分法，都是一看就会，一写就废](./problems/0704.二分查找.md)
3. [数组：就移除个元素很难么？](./problems/0027.移除元素.md)
4. [数组：滑动窗口拯救了你](https://mp.weixin.qq.com/s/UrZynlqi4QpyLlLhBPglyg)
5. [数组：这个循环可以转懵很多人！](https://mp.weixin.qq.com/s/KTPhaeqxbMK9CxHUUgFDmg)
6. [数组：总结篇](https://mp.weixin.qq.com/s/LIfQFRJBH5ENTZpvixHEmg)
4. [数组：滑动窗口拯救了你](./problems/0209.长度最小的子数组.md)
5. [数组：这个循环可以转懵很多人！](./problems/0059.螺旋矩阵II.md)
6. [数组：总结篇](./problems/数组总结篇.md)

## 链表

1. [关于链表，你该了解这些！](https://mp.weixin.qq.com/s/ntlZbEdKgnFQKZkSUAOSpQ)
2. [链表：听说用虚拟头节点会方便很多？](https://mp.weixin.qq.com/s/slM1CH5Ew9XzK93YOQYSjA)
3. [链表：一道题目考察了常见的五个操作！](https://mp.weixin.qq.com/s/Cf95Lc6brKL4g2j8YyF3Mg)
4. [链表：听说过两天反转链表又写不出来了？](https://mp.weixin.qq.com/s/pnvVP-0ZM7epB8y3w_Njwg)
5. [链表：删除链表的倒数第 N 个结点](https://leetcode-cn.com/problems/remove-nth-node-from-end-of-list/solution/dai-ma-sui-xiang-lu-19-shan-chu-lian-bia-2hxt/)
5. [链表：环找到了，那入口呢？](https://mp.weixin.qq.com/s/_QVP3IkRZWx9zIpQRgajzA)
6. [链表：总结篇！](https://mp.weixin.qq.com/s/vK0JjSTHfpAbs8evz5hH8A)
1. [关于链表，你该了解这些！](./problems/链表理论基础.md)
2. [链表：听说用虚拟头节点会方便很多？](./problems/0203.移除链表元素.md)
3. [链表：一道题目考察了常见的五个操作！](./problems/0707.设计链表.md)
4. [链表：听说过两天反转链表又写不出来了？](./problems/0206.翻转链表.md)
5. [链表：删除链表的倒数第 N 个结点](./problems/0019.删除链表的倒数第N个节点.md)
5. [链表：环找到了，那入口呢？](./problems/0142.环形链表II.md)
6. [链表：总结篇！](./problems/链表总结篇.md)

## 哈希表

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## 字符串

1. [字符串：这道题目，使用库函数一行代码搞定](https://mp.weixin.qq.com/s/X02S61WCYiCEhaik6VUpFA)
2. [字符串：简单的反转还不够！](https://mp.weixin.qq.com/s/XGSk1GyPWhfqj2g7Cb1Vgw)
3. [字符串：替换空格](https://mp.weixin.qq.com/s/t0A9C44zgM-RysAQV3GZpg)
4. [字符串：花式反转还不够！](https://mp.weixin.qq.com/s/X3qpi2v5RSp08mO-W5Vicw)
5. [字符串：反转个字符串还有这个用处？](https://mp.weixin.qq.com/s/PmcdiWSmmccHAONzU0ScgQ)
6. [帮你把KMP算法学个通透！（理论篇）B站视频](https://www.bilibili.com/video/BV1PD4y1o7nd)
7. [帮你把KMP算法学个通透！（代码篇）B站视频](https://www.bilibili.com/video/BV1M5411j7Xx)
8. [字符串：都来看看KMP的看家本领！](https://mp.weixin.qq.com/s/Gk9FKZ9_FSWLEkdGrkecyg)
9. [字符串：KMP算法还能干这个！](https://mp.weixin.qq.com/s/lR2JPtsQSR2I_9yHbBmBuQ)
10. [字符串：前缀表不右移，难道就写不出KMP了？](https://mp.weixin.qq.com/s/p3hXynQM2RRROK5c6X7xfw)
11. [字符串：总结篇！](https://mp.weixin.qq.com/s/gtycjyDtblmytvBRFlCZJg)
1. [字符串：这道题目，使用库函数一行代码搞定](./problems/0344.反转字符串.md)
2. [字符串：简单的反转还不够！](./problems/0541.反转字符串II.md)
3. [字符串：替换空格](./problems/剑指Offer05.替换空格.md)
4. [字符串：花式反转还不够！](./problems/0151.翻转字符串里的单词.md)
5. [字符串：反转个字符串还有这个用处？](./problems/剑指Offer58-II.左旋转字符串.md)
6. [帮你把KMP算法学个通透](./problems/0028.实现strStr.md)
8. [字符串：KMP算法还能干这个！](./problems/0459.重复的子字符串.md)
9. [字符串：总结篇！](./problems/字符串总结.md)

## 双指针法

双指针法基本都是应用在数组，字符串与链表的题目上

1. [数组：就移除个元素很难么？](https://mp.weixin.qq.com/s/wj0T-Xs88_FHJFwayElQlA)
2. [字符串：这道题目，使用库函数一行代码搞定](https://mp.weixin.qq.com/s/X02S61WCYiCEhaik6VUpFA)
3. [字符串：替换空格](https://mp.weixin.qq.com/s/t0A9C44zgM-RysAQV3GZpg)
4. [字符串：花式反转还不够！](https://mp.weixin.qq.com/s/X3qpi2v5RSp08mO-W5Vicw)
5. [链表：听说过两天反转链表又写不出来了？](https://mp.weixin.qq.com/s/pnvVP-0ZM7epB8y3w_Njwg)
6. [链表：环找到了，那入口呢？](https://mp.weixin.qq.com/s/_QVP3IkRZWx9zIpQRgajzA)
1. [数组：就移除个元素很难么？](./problems/0027.移除元素.md)
2. [字符串：这道题目，使用库函数一行代码搞定](./problems/0344.反转字符串.md)
3. [字符串：替换空格](./problems/剑指Offer05.替换空格.md)
4. [字符串：花式反转还不够！](./problems/0151.翻转字符串里的单词.md)
5. [链表：听说过两天反转链表又写不出来了？](./problems/0206.翻转链表.md)
6. [链表：环找到了，那入口呢？](./problems/0142.环形链表II.md)
7. [哈希表：解决了两数之和，那么能解决三数之和么？](https://mp.weixin.qq.com/s/r5cgZFu0tv4grBAexdcd8A)
8. [双指针法：一样的道理，能解决四数之和](https://mp.weixin.qq.com/s/nQrcco8AZJV1pAOVjeIU_g)
9. [双指针法：总结篇！](https://mp.weixin.qq.com/s/_p7grwjISfMh0U65uOyCjA)
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<p align="center">
<a href="https://mp.weixin.qq.com/s/QVF6upVMSbgvZy8lHZS3CQ"><img src="https://img.shields.io/badge/知识星球-代码随想录-blue" alt=""></a>
<a href="https://mp.weixin.qq.com/s/b66DFkOp8OOxdZC_xLZxfw"><img src="https://img.shields.io/badge/刷题-微信群-green" alt=""></a>
<a href="https://img-blog.csdnimg.cn/20201210231711160.png"><img src="https://img.shields.io/badge/公众号-代码随想录-brightgreen" alt=""></a>
<a href="https://space.bilibili.com/525438321"><img src="https://img.shields.io/badge/B站-代码随想录-orange" alt=""></a>
</p>

## 19.删除链表的倒数第N个节点

## 思路

双指针的经典应用，如果要删除倒数第n个节点，让fast移动n步，然后让fast和slow同时移动，直到fast指向链表末尾。删掉slow所指向的节点就可以了。

思路是这样的，但要注意一些细节。

分为如下几步：

* 首先这里我推荐大家使用虚拟头结点，这样方面处理删除实际头结点的逻辑，如果虚拟头结点不清楚，可以看这篇： [链表：听说用虚拟头节点会方便很多？](https://mp.weixin.qq.com/s/slM1CH5Ew9XzK93YOQYSjA)


* 定义fast指针和slow指针，初始值为虚拟头结点，如图：

<img src='https://code-thinking.cdn.bcebos.com/pics/19.%E5%88%A0%E9%99%A4%E9%93%BE%E8%A1%A8%E7%9A%84%E5%80%92%E6%95%B0%E7%AC%ACN%E4%B8%AA%E8%8A%82%E7%82%B9.png' width=600> </img></div>

* fast首先走n + 1步 ，为什么是n+1呢，因为只有这样同时移动的时候slow才能指向删除节点的上一个节点（方便做删除操作），如图：
<img src='https://code-thinking.cdn.bcebos.com/pics/19.%E5%88%A0%E9%99%A4%E9%93%BE%E8%A1%A8%E7%9A%84%E5%80%92%E6%95%B0%E7%AC%ACN%E4%B8%AA%E8%8A%82%E7%82%B91.png' width=600> </img></div>

* fast和slow同时移动，之道fast指向末尾，如题：
<img src='https://code-thinking.cdn.bcebos.com/pics/19.%E5%88%A0%E9%99%A4%E9%93%BE%E8%A1%A8%E7%9A%84%E5%80%92%E6%95%B0%E7%AC%ACN%E4%B8%AA%E8%8A%82%E7%82%B92.png' width=600> </img></div>

* 删除slow指向的下一个节点，如图：
<img src='https://code-thinking.cdn.bcebos.com/pics/19.%E5%88%A0%E9%99%A4%E9%93%BE%E8%A1%A8%E7%9A%84%E5%80%92%E6%95%B0%E7%AC%ACN%E4%B8%AA%E8%8A%82%E7%82%B93.png' width=600> </img></div>

此时不难写出如下C++代码：

```C++
class Solution {
public:
ListNode* removeNthFromEnd(ListNode* head, int n) {
ListNode* dummyHead = new ListNode(0);
dummyHead->next = head;
ListNode* slow = dummyHead;
ListNode* fast = dummyHead;
while(n-- && fast != NULL) {
fast = fast->next;
}
fast = fast->next; // fast再提前走一步，因为需要让slow指向删除节点的上一个节点
while (fast != NULL) {
fast = fast->next;
slow = slow->next;
}
slow->next = slow->next->next;
return dummyHead->next;
}
};
```
## 其他语言补充
java:
```java
class Solution {
public ListNode removeNthFromEnd(ListNode head, int n) {
ListNode dummy = new ListNode(-1);
dummy.next = head;
ListNode slow = dummy;
ListNode fast = dummy;
while (n-- > 0) {
fast = fast.next;
}
// 记住 待删除节点slow 的上一节点
ListNode prev = null;
while (fast != null) {
prev = slow;
slow = slow.next;
fast = fast.next;
}
// 上一节点的next指针绕过 待删除节点slow 直接指向slow的下一节点
prev.next = slow.next;
// 释放 待删除节点slow 的next指针, 这句删掉也能AC
slow.next = null;
return dummy.next;
}
}
```

------------------------

* 微信：[程序员Carl](https://mp.weixin.qq.com/s/b66DFkOp8OOxdZC_xLZxfw)
* B站：[代码随想录](https://space.bilibili.com/525438321)
* 知识星球：[代码随想录](https://mp.weixin.qq.com/s/QVF6upVMSbgvZy8lHZS3CQ)

![](../pics/公众号.png)

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