[LeetCode] strStr

Implement strStr().

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

Update (2014-11-02):
The signature of the function had been updated to return the index instead of the pointer. If you still see your function signature returns a char * or String, please click the reload button  to reset your code definition.

class Solution {
public:
    int strStr(string haystack, string needle) {
        string::size_type pos = 0;
        if (( pos = haystack.find(needle)) != string::npos)
            return pos;
        else
            return -1;
    }
};