28_Implement_strStr.py

#!/usr/bin/python
# -*- coding: utf-8 -*-
"""
Desc: 28. 实现 strStr()  (简单)
Author: wangluyu
Date: 2020/1/14
"""


class Solution:
    """
    Implement strStr().
    Return the index of the first occurrence of needle in haystack, or -1 if needle is not part of haystack.
    Example 1:
    Input: haystack = "hello", needle = "ll"
    Output: 2
    Example 2:
    Input: haystack = "aaaaa", needle = "bba"
    Output: -1
    Clarification:
    What should we return when needle is an empty string? This is a great question to ask during an interview.
    For the purpose of this problem, we will return 0 when needle is an empty string. This is consistent to C's strstr() and Java's indexOf().
    实现 strStr() 函数。
    给定一个 haystack 字符串和一个 needle 字符串，在 haystack 字符串中找出 needle 字符串出现的第一个位置 (从0开始)。如果不存在，则返回  -1。
    示例 1:
    输入: haystack = "hello", needle = "ll"
    输出: 2
    示例 2:
    输入: haystack = "aaaaa", needle = "bba"
    输出: -1
    说明:
    当 needle 是空字符串时，我们应当返回什么值呢？这是一个在面试中很好的问题。
    对于本题而言，当 needle 是空字符串时我们应当返回 0 。这与C语言的 strstr() 以及 Java的 indexOf() 定义相符。
    """
    def strStr(self, haystack: str, needle: str) -> int:
        if needle == "":
            return 0
        needle_len = len(needle)
        haystack_len = len(haystack)
        if needle_len > haystack_len:
            return -1
        elif needle_len == haystack_len and haystack == needle:
            return 0
        for i in range(haystack_len - needle_len + 1):
            if needle == haystack[i:i+needle_len]:
                return i
        return -1

    def strStr_KMP(self, haystack: str, needle: str) -> int:
        # TODO KMP实现
        return -1


if __name__ == '__main__':
    haystack = "mississippi"
    needle = "pi"
    s = Solution()
    print(s.strStr(haystack, needle))