[LeetCode-28] Implement strStr（KMP 字符串匹配）

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Implement strStr().

Returns the index of the first occurrence of needle in haystack, or -1 if needle is not part of haystack.

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【解题思路】

采用字符串匹配算法 KMP 算法的思想

void getNext(char *strSub,int *strSubnext)  {if(!strSub||!strSubnext)return;int strSubLen = strlen(strSub);int i = 0;/*后缀字符的当前位置*/int j = -1;/*前缀字符的当前位置*/strSubnext[0] = -1;while(i<(strSubLen-1)) {if(j==-1||strSub[i]==strSub[j]) { /*后缀字符和前缀字符相等时*/i++;j++;strSubnext[i] = j;/*前缀字符当前对应值是在后缀位置+1*/} else {j = strSubnext[j];/*回溯回去，回到后缀位置*/}}}int strStr(char* haystack, char* needle){if(!haystack||!needle) {return -1;}int srcStringLen = strlen(haystack);int keyStringLen = strlen(needle);if(srcStringLen<keyStringLen)return -1;if(srcStringLen==0||keyStringLen==0)return 0;int *strSubnext = (int *)malloc(sizeof(int)*(keyStringLen));int i = 0;int j = 0;getNext(needle,strSubnext);while(i<srcStringLen&&j<keyStringLen) {if(j==-1||haystack[i]==needle[j]) {++i;++j;} else {j = strSubnext[j];}if(j==keyStringLen) {free(strSubnext);return (i-keyStringLen);/*返回当前位置*/}}return -1; /*没找到*/}

完整代码如下：

// LeetCode28-Implement strStr.cpp : 定义控制台应用程序的入口点。//LeetCode28-Implement strStr//Written by ZP1015//2015.11.20#include "stdafx.h"#include <stdio.h>#include <stdlib.h>#include <string.h>#include<time.h>void getNext(char *strSub,int *strSubnext)  {if(!strSub||!strSubnext)return;int strSubLen = strlen(strSub);int i = 0;/*后缀字符的当前位置*/int j = -1;/*前缀字符的当前位置*/strSubnext[0] = -1;while(i<(strSubLen-1)) {if(j==-1||strSub[i]==strSub[j]) { /*后缀字符和前缀字符相等时*/i++;j++;strSubnext[i] = j;/*前缀字符当前对应值是在后缀位置+1*/} else {j = strSubnext[j];/*回溯回去，回到后缀位置*/}}}int strStr(char* haystack, char* needle){if(!haystack||!needle) {return -1;}int srcStringLen = strlen(haystack);int keyStringLen = strlen(needle);if(srcStringLen<keyStringLen)return -1;if(srcStringLen==0||keyStringLen==0)return 0;int *strSubnext = (int *)malloc(sizeof(int)*(keyStringLen));int i = 0;int j = 0;getNext(needle,strSubnext);while(i<srcStringLen&&j<keyStringLen) {if(j==-1||haystack[i]==needle[j]) {++i;++j;} else {j = strSubnext[j];}if(j==keyStringLen) {free(strSubnext);return (i-keyStringLen);/*返回当前位置*/}}return -1; /*没找到*/}int main(){clock_t start,stop;double duringtime;start = clock();char *srcString ="aaaab";char *keyString = "b";int result = strStr(srcString, keyString);printf("%d\n",result);stop = clock();duringtime=(double)(stop-start)/CLOCKS_PER_SEC;printf("%f\n",duringtime);getchar();return 0;}

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