567. Permutation in String 
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Problem
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 <= 104s1ands2consist of lowercase English letters.