028._implement_strstr().md

28. Implement strStr()

难度: Easy

刷题内容

原题连接

• https://leetcode.com/problems/implement-strstr/description/

内容描述

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().

解题方案

思路 1

一行解法如何？

class Solution(object):
    def strStr(self, haystack, needle):
        """
        :type haystack: str
        :type needle: str
        :rtype: int
        """
        return haystack.find(needle)

思路 2

这个题目其实可以引来一大类，那就是关于string的算法，但是此处先用暴力算法来AC，然后再来细读/品味别的string相关算法吧。

虽然是暴力算法，但是也不容易写对啊

class Solution(object):
    def strStr(self, haystack, needle):
        """
        :type haystack: str
        :type needle: str
        :rtype: int
        """
        if not needle or len(needle) == 0:
            return 0
        for i in range(len(haystack)-len(needle)+1):
            if haystack[i] == needle[0]:
                j = 1
                while j < len(needle) and haystack[i+j] == needle[j]:
                    j += 1
                if j == len(needle):
                    return i
        return -1