28. Implement strStr() (String)

Implement strStr().

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

class Solution {
public:
    int strStr(string haystack, string needle) {
        int firstPos = 0;
        int i, j;
        int haySize = haystack.length();
        int needleSize = needle.length();
        
        if(needleSize == 0) return 0;
        
        for(i = 0; i < haySize; firstPos++){
            i = firstPos;
            for(j = 0; j < needleSize && i < haySize; j++, i++){
                if(needle[j]!=haystack[i]) break;
            }
            if(j == needleSize) return firstPos;
        }
        return -1;
    }
};