# LeetCode 28：Implement strStr()

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().

`package com.lihuia.leetcode28;/** * Copyright (C), lihuia.com * FileName: Solution * Author:   lihui * Date:     2018/7/24 */public class Solution {     public int strStr(String haystack, String needle) {         int maxLen = haystack.length();         int subLen = needle.length();                  int currentIndex = 0;         int currentPos = 0;                  for (int i = 0; i < maxLen - subLen + 1; i++) {             for (int j = 0; j < subLen; j++) {                 currentIndex = i + j;                 if (haystack.charAt(currentIndex) != needle.charAt(j)) {                     break;                 }                 currentPos = j + 1;             }                          if (currentPos == subLen) {                 return i;             }         }         return -1;    }}`