LeetCode 實現strStr()

# Leetcode 實現strStr()
# 找子串的問題 一遍遍歷就行了 很簡單
class Solution:
    def strStr(self, haystack: str, needle: str) -> int:
        if haystack == "" and needle == "":
            return 0
        elif haystack == "" and len(needle) > 0:
            return -1
        elif len(haystack) > 0 and needle == "":
            return 0
        else:
            len_needle = len(needle)
            len_haystack = len(haystack)
            if len_haystack < len_needle:
                return -1
            else:
                i = 0
                while i <= len_haystack - 1:
                    if haystack[i:i+len_needle] == needle:
                        return i
                    else:
                        i += 1
                return -1