public class Solution
extends Object
854 - K-Similar Strings\.
Hard
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
**Example 2:**
**Input:** s1 = "abc", s2 = "bca"
**Output:** 2
**Constraints:**
* `1 <= s1.length <= 20`
* `s2.length == s1.length`
* `s1` and `s2` contain only lowercase letters from the set `{'a', 'b', 'c', 'd', 'e', 'f'}`.
* `s2` is an anagram of `s1`.