LeetCode: 28. 实现strStr() #71

class Solution:
    def strStr(self, haystack, needle):
        """
        :type haystack: str
        :type needle: str
        :rtype: int
        """
        if len(needle) == 0:
            return 0
        
        needle_len = len(needle)
        haystack_len = len(haystack)
        if needle_len > haystack_len:
            return -1
        
        for index in range(haystack_len - needle_len + 1):
            find = 0
            for s2 in needle:
                if haystack_len > find + index and s2 == haystack[find + index]:
                    find += 1
                else:
                    break
            if find == needle_len:
                return index
        return -1