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# Implement strStr()

## Problem

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`.

{% hint style="info" %}
For example:

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

```
Input: haystack = "aaaaa", needle = "bba"
Output: -1
```

```
Input: haystack = "", needle = ""
Output: 0
```

{% endhint %}

## Solution

```
class Solution:
    def strStr(self, haystack: str, needle: str) -> int:
        
        length = len(needle)
        if needle == "":
            return 0
        
        for i in range(len(haystack)):
            if haystack[i:i+length] == needle:
                return i
        return -1
        
#Time: O(n)
#Space: O(1)

#Its just substring matching
```