Leetcode028. Implement strStr()

class Solution {
public:
    int strStr(string haystack, string needle) {
        if(needle.empty())return ;    //needle empty
        if(haystack.empty()) return -;    //haystack empty
        for(int i = , j = ; i+j < haystack.size();) {
            if(haystack[i+j] != needle[j])i++, j = ;     //no equal   needle index to 0, haystack index move to next.
            else j++;   //equal both move to next
            if(j == needle.size())return i;     //thr first time find substr.
        }
        return -;
    }
};