567. Permutation in String

Medium

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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.

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