Implement strStr(). Returns a pointer to the first occurrence of needle in haystack, or null if needle is not part of haystack. http://leetcode.com/onlinejudge

leetcode_strstr.cpp

class Solution {
public:
    char *strStr(char *haystack, char *needle) {
        if (*haystack == NULL && *needle == NULL)
            return haystack;
        char* ret;
        for (ret = haystack; *ret != NULL; ++ret) {
            int k;
            for (k = 0; needle[k] != NULL; ++k)
                if (ret[k] != needle[k])
                    break;
            if (needle[k] == NULL)
                return ret;
            if (ret[k] == NULL)
                break;
        }
        return NULL;
    }
};