LeetCode 28. Implement strStr() C语言

题目描述：

Implement strStr().

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

意思就是找到匹配字符串开始的位置，kmp算法。

我的代码：

int strStr(char* haystack, char* needle) {
    int a = 0;
    int b = 0;
    int A = strlen(haystack);
    int B=  strlen(needle);
    if(B==0){
        return 0;
    }
    int index = -1;
    while(a<A&&b<B){
        if(haystack[a] == needle[b]){
            if(b == 0){
                index = a;
            }
            a++;
            b++;
        }
        else{
            a++;
            b = 0;
            if(index != -1){
                a = index + 1;
                index = -1;
            }
        }
    }
    if(b == B){
        return index;
    }
    return -1;
}