# 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.

```python
from collections import defaultdict
class Solution:
    def checkInclusion(self, s1: str, s2: str) -> bool:
        d1 = defaultdict(int)
        d2 = defaultdict(int)
        for s in s1:
            d1[s] += 1
        for s in s2[:len(s1)]:
            d2[s] += 1
        i = 0
        j = len(s1)
        while j < len(s2):
            if d1 == d2:
                return True
            d2[s2[i]] -= 1
            if d2[s2[i]] < 1:
                d2.pop(s2[i])
            d2[s2[j]] = d2[s2[j]] + 1
            i += 1
            j += 1
        return d1 == d2
        
```