# [28. Implement strStr()](https://leetcode.com/problems/implement-strstr/)

## 题目

Implement strStr().

Return the index of the first occurrence of needle in haystack, or -1 if needle is not part of haystack.


Example 1:

```c
Input: haystack = "hello", needle = "ll"
Output: 2
```

Example 2:

```c
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().

## 题目大意


实现一个查找 substring 的函数。如果在母串中找到了子串，返回子串在母串中出现的下标，如果没有找到，返回 -1，如果子串是空串，则返回 0 。

## 解题思路

这一题比较简单，直接写即可。