Problem:###

Implement strStr().
Returns the index of the first occurrence of needle in haystack, or -1 if needle is not part of haystack.

Solution:###

class Solution {
public:
    int strStr(string haystack, string needle) {
        if(haystack == needle)
            return 0;
        if(haystack.size() < needle.size())
            return -1;
        for(int i = 0;i <= haystack.size() - needle.size();i++) //notice the <= here
        {
            if(haystack.substr(i,needle.size()) == needle)
                return i;
        }
        return -1;
    }
};

Memo###

the use of substr