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# 567. Permutation in String

## Medium

***

Given two strings `s1` and `s2`, return `true` *if* `s2` *contains a permutation of* `s1`*, or* `false` *otherwise*.

In other words, return `true` if one of `s1`'s permutations is the substring of `s2`.

 

**Example 1:**

```
Input: s1 = "ab", s2 = "eidbaooo"
Output: true
Explanation: s2 contains one permutation of s1 ("ba").
```

**Example 2:**

```
Input: s1 = "ab", s2 = "eidboaoo"
Output: false
```

 

**Constraints:**

* `1 <= s1.length, s2.length <= 104`
* `s1` and `s2` consist of lowercase English letters.