854. K-Similar Strings

Strings s1 and s2 are k-similar (for some non-negative integer k) if we can swap the positions of two letters in s1 exactly k times so that the resulting string equals s2. Given two anagrams s1 and s2, return the smallest k for which s1 and s2 are k-similar. Example 1: Input: s1 = "ab", s2 = "ba" Output: 1 Explanation: The two string are 1-similar because we can use one swap to change s1 to s