KMP算法(字符串匹配)

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KMP算法

基本思想：

求next数组：

代码实现：

#include <stdio.h>#include <string.h>#include <assert.h>#include <stdlib.h>static void GetNext(const char *str,int *next){int len = strlen(str);next[0] = -1;next[1] = 0;int j = 1;int k = 0;while(j + 1 < len){if((k == -1) || (str[k] == str[j]))//Pk == Pj{next[++j] = ++k;}else//Pk != Pj{k = next[k];//k相当于KMP中的j}}}int KMP(const char *str,const char *sub,int pos)//O(m+n){assert(str != NULL && sub != NULL && pos >= 0);int i = pos;int j = 0;int lenstr = strlen(str);int lensub = strlen(sub);int *next = (int *)malloc(lensub *sizeof(int));GetNext(sub,next);while(i < lenstr && j < lensub){if((j == -1) || (str[i] == sub[j])){i++;j++;}else{j = next[j];//i不用回退}}free(next);if(j >= lensub){return i - j;}else{return -1;}}int main(){printf("%d\n",KMP("ababcabcdabcde","abcdf",0));printf("%d\n",KMP("ababcabcdabcde","abcd",4));printf("%d\n",KMP("ababcabcdabcde","abc",8));return 0;}

运行结果：

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