class Solution:

    def strStr(self, haystack, needle):

        """

        :type haystack: str

        :type needle: str

        :rtype: int

        """

        # 法一

        # n = len(haystack)

        # m = len(needle)

        # if not m or haystack == needle:

        #     return 0

        # if n < m:

        #     return -1

        # for i in range(n-m+1):

        #     if haystack[i:i+m] == needle:

        #         return i

        # return -1

        # 法二

        # if needle in haystack:

        #     return haystack.index(needle)

        # elif not needle or haystack == needle:

        #     return 0

        # else:

        #     return -1

        # 法三

        return haystack.find(needle)