暴力双指针

class Solution {
public:
    int strStr(string haystack, string needle) {
        int i, j, k;
        i = j = k = 0;
        while(i < haystack.size() && j < needle.size()){
            if(haystack[k] == needle[j])    k ++, j ++ ;
            else{
                j = 0;
                i ++ ;
                k = i;
                if(haystack.size() - k + 1 < needle.size()) return -1;
            }
        }
        if(j == needle.size())  return i;
        return -1;
    }
};

KMP(待续)