567. Permutation in String

Problem Link

Description

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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.

Solution

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Python3

class Solution:
    def checkInclusion(self, s1: str, s2: str) -> bool:
        mp = collections.Counter(s1)
        i = 0
        
        for j, x in enumerate(s2):
            mp[x] -= 1
            
            while mp[x] < 0:
                mp[s2[i]] += 1
                i += 1
            
            if j - i + 1 == len(s1):
                return True
        
        return False