class Solution(object):

    def strStr(self, haystack, needle):

        """

        :type haystack: str

        :type needle: str

        :rtype: int

        """

        if not needle:

            return 0

        n_len = len(needle)

        h_len = len(haystack)

        if n_len > h_len:

            return -1

        elif n_len == h_len:

            if haystack == needle:

                return 0

            return -1

        for i in range(h_len-n_len+1):

            if haystack[i:i+n_len] == needle:

                return i

        return -1