# 28. Implement strStr()

Implement [strStr()](http://www.cplusplus.com/reference/cstring/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()](http://www.cplusplus.com/reference/cstring/strstr/) and Java's [indexOf()](https://docs.oracle.com/javase/7/docs/api/java/lang/String.html#indexOf\(java.lang.String\)).

**Solution**

```
class Solution {
    public int strStr(String haystack, String needle) {
        for(int i = 0;; i++) {
            for(int j = 0;; j++){
                //if it goes to the end of needle without problems
                if(j == needle.length()) return i;
                //check if we are end of haystack
                if(i+j == haystack.length()) return -1;
                //check if the char is equal
                if(haystack.charAt(i+j) != needle.charAt(j)) break;
            }
        }
    }
}
```
