implement strStr

/*Implement strStr().Returns the index of the first occurrence of needle in haystack, or -1 if needle is not part of haystack.寻找子串并返回第一次出现的位置，采用KMP算法来解决。KMP算法的核心是无回溯，利用next数字记录子串每次失配后应该从子串的何处继续匹配，重点在于next数组的求解。*/#include <stdio.h>#include <string.h>void get_next(char *t,int *next){int i=0,j=-1;next[0]=-1;while(t[i]!='\0'){if(j==-1 || t[i]==t[j]){i++,j++;if(t[i]!=t[j])next[i]=j;elsenext[i]=next[j];}elsej=next[j];}}int KMP(char *s,char *t,int *next){if(s==NULL || t==NULL)return -1;int i=0,j=0;int len=strlen(t);if(len==0) return 0;//空串 ""while(s[i]!='\0'){if(j==-1 || s[i]==t[j])i++,j++;elsej=next[j];if(j==len)return i-len; }return -1;}int strStr(char* haystack, char* needle){int needle_len=strlen(needle);printf("len:%d\n",needle_len);int next[needle_len+1];get_next(needle,next);return KMP(haystack,needle,next);    }int main(int argc,char **argv){char s[128]="";char t[64]="";printf("%d\n",strStr(s,t));return 0;}