Permutation in String

Permutation in String

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

Input: s1 = “ab”, s2 = “eidbaooo”

Output: true

Explanation: s2 contains one permutation of s1 (“ba”).

Approach 1:

Implementation:

from collections import Counter
class Solution:


    def checkInclusion(self, s1: str, s2: str) -> bool:
        if len(s1) > len(s2):
            return False
        dict_1 = Counter(s1)
        matched = 0
        required = len(dict_1)
        for i in range(len(s2)):
            if s2[i] in dict_1:
                dict_1[s2[i]] -= 1
                if dict_1[s2[i]] == 0:
                    matched += 1
            if i >= len(s1) and s2[i - len(s1)] in dict_1:
                if dict_1[s2[i - len(s1)]] == 0:
                    matched -= 1
                dict_1[s2[i-len(s1)]] += 1
            if matched == required:
                return True
        return False
        
        

Complexity Analysis:

Time Complexity: O(len(s1) + len(s2))

Space Complexity: O(len(s1)) for the hashmap created by the Counter

Reflection

I should really work hard on these questions:)