> For the complete documentation index, see [llms.txt](https://maksimdan.gitbook.io/interview-practice-problems/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://maksimdan.gitbook.io/interview-practice-problems/leetcode_sessions/567-permutation-in-string.md).

# 567 Permutation in String

Given two strings s1 and s2, write a function to return true if s2 contains the permutation of s1. In other words, one of the first string's permutations is the substring of the second string.

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

```
Input:s1= "ab" s2 = "eidboaoo"
Output: False
```

Note: 1. The input strings only contain lower case letters. 2. The length of both given strings is in range \[1, 10,000].

**Brute Force Approach**: Every substring of length |s1| in |s2| and find at least one instance of where the sorted substring == sorted s1.

**Time Complexity**: Let s1 be len(s1) and s2 be len(s2). O((s1-s2)\*s1logs1 + s1(s1-s2)) for sorting each substring and string comparison.

```python
def checkInclusion(self, s1, s2):
    """
    :type s1: str
    :type s2: str
    :rtype: bool
    """

    sorted_s1 = sorted(s1)
    go_till = len(s2) - len(s1) + 1
    for i in range(0, go_till):
        if sorted_s1 == sorted(s2[i:i+len(s1)]):
            return True

    return False
```


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