From 768c60cf6c60cd0370f70492cc8f5e0bc4979347 Mon Sep 17 00:00:00 2001
From: Leon <LiXiao.Dev@gmail.com>
Date: Thu, 6 May 2021 06:21:56 +0800
Subject: [PATCH] =?UTF-8?q?feat:=20KMP=20=E7=AE=97=E6=B3=95?=
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---
 __test__/strings/index.spec.ts | 16 ++++++------
 src/algs4/strings/kmp.ts       | 47 +++++++++++++++++-----------------
 2 files changed, 31 insertions(+), 32 deletions(-)

diff --git a/__test__/strings/index.spec.ts b/__test__/strings/index.spec.ts
index 88e4a378..b7029bc7 100644
--- a/__test__/strings/index.spec.ts
+++ b/__test__/strings/index.spec.ts
@@ -172,12 +172,12 @@ describe('字符串算法测试', () => {
     })
   })
 
-  // describe('KMP', () => {
-  //   test('KMP 构造函数 lix', () => {
-  //     const kmp = new KMP('ababac')
-  //     expect(kmp).not.toBeNull()
-  //     const index = kmp.search('aaaaabbbbbababacaaaaaaaaaaaaaaaaaa')
-  //     expect(index).toBe(0)
-  //   })
-  // })
+  describe('KMP', () => {
+    test('KMP 构造函数 lix', () => {
+      const kmp = new KMP('ababac')
+      expect(kmp).not.toBeNull()
+      const index = kmp.search('aaaaabbbbbababacaaaaaaaaaaaaaaaaaa')
+      expect(index).toBe(10)
+    })
+  })
 })
diff --git a/src/algs4/strings/kmp.ts b/src/algs4/strings/kmp.ts
index 1efce3f5..88559f82 100644
--- a/src/algs4/strings/kmp.ts
+++ b/src/algs4/strings/kmp.ts
@@ -1,41 +1,40 @@
-const ACode = 97
+const RADIX = 256
 
 export default class KMP {
   private pat: string
   private dfa: number[][]
 
+  // 由模式字符串构造 DFA
   constructor(pat: string) {
     this.pat = pat
-    const M = pat.length
-    const R = 26
-    this.dfa = Array.from({ length: R }, () => [])
-    for (const sub of this.dfa) {
-      for (let i = 0; i < M; i++) {
-        sub[i] = null
-      }
+    this.dfa = new Array(RADIX)
+    const n = this.pat.length
+    for (let i = 0; i < RADIX; i++) {
+      this.dfa[i] = new Array(n).fill(0)
     }
-    this.dfa[this.pat.charCodeAt(0) - ACode][0] = 1
 
-    for (let X = 0, j = 1; j < M; j++) {
-      for (let c = 0; c < R; c++) {
-        this.dfa[c][j] = this.dfa[c][X]
+    this.dfa[this.pat.charCodeAt(0)][0] = 1
+
+    // 计算 dfa[][curr]
+    for (let prev = 0, curr = 1; curr < n; curr++) {
+      for (let ch = 0; ch < RADIX; ch++) {
+        this.dfa[ch][curr] = this.dfa[ch][prev] // 复制匹配失败情况下的值
       }
-      this.dfa[this.pat.charCodeAt(j) - ACode][j] = j + 1
-      X = this.dfa[this.pat.charCodeAt(j) - ACode][X]
+      this.dfa[this.pat.charCodeAt(curr)][curr] = curr + 1 // 设置匹配成功情况下的值
+      prev = this.dfa[this.pat.charCodeAt(curr)][prev] // 更新重启状态
     }
   }
 
-  search(txt: string): number {
+  // 在 txt 上模拟 DFA 的运行
+  search(txt: string) {
     let i, j
-    const N = txt.length
-    const M = this.pat.length
-    for (i = 0, j = 0; i < N && j < M; i++) {
-      j = this.dfa[txt.charCodeAt(i) - ACode][j]
-    }
-    if (j === M) {
-      return i - M
-    } else {
-      return N
+    const m = this.pat.length
+    const n = txt.length
+    for (i = 0, j = 0; i < n && j < m; i++) {
+      j = this.dfa[txt.charCodeAt(i)][j]
     }
+
+    // 找到匹配（到达模式字符串的结尾）则返回 i-m
+    return j === m ? i - m : -1
   }
 }