23.字符串匹配，KMP算法

#include<stdio.h>#include<string.h>#include<stdlib.h>#include<assert.h>//BF算法(一般思路的字符串匹配)int BF(const char *s, const char *sub, int pos)  //pos表示从s的pos位置处开始匹配{int i = pos;int j = 0;int lens = strlen(s);int lensub = strlen(sub);while ((i < lens) && (j < lensub)){if (s[i] == sub[j]){i++;j++;}else{i = i - j + 1;  //匹配失败，i回到开始匹配位置+1的下标处，j=0j = 0;}}if (j >= lensub){return i - j;}else{return -1;}}//KMP算法void GetNext(int *next, const char *sub){int lensub = strlen(sub);next[0] = -1;next[1] = 0;int i = 2;int k = 0;while (i < lensub){if ((k == -1) || (sub[i - 1] == sub[k])){//next[i] = k + 1;//i++;//k += 1;next[i++] = ++k;}else{k = next[k];  //不是k = next[i]，因为是在k位置处出现失配}}//对next数组进行优化，当发生不匹配且next[j]元素与当前j下标元素相同，直接跳过，减少不必要的匹配for (int j = 1; j < lensub; j++){if (sub[next[j]] == sub[j]){next[j] = next[next[j]];}}}int KMP(const char *s, const char *sub, int pos){int i = pos;int j = 0;int lens = strlen(s);int lensub = strlen(sub);int *next = (int*)malloc(lensub * sizeof(int));assert(next != NULL);GetNext(next, sub);  //得到sub的next数组while (i < lens && j < lensub){if ((j == -1) || (s[i] == sub[j])){i++;j++;}else{j = next[j];//匹配不相等时只改变j下标，i不用回退}}free(next);if (j >= lensub){return i - j;}else{return -1;}}int main(){char *s = "abcabababcabd";char *sub = "abcabd";//int pos = BF(s, sub, 0);int pos = KMP(s, sub, 0);printf("%d\n", pos);return 0;}