854. K-Similar Strings

Hard

50 Points

Hash Table

String

Breadth-First Search

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.

Examples

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 s2: "ab" --> "ba".

Example 2

Input: s1 = "abc", s2 = "bca" Output: 2 Explanation: The two strings are 2-similar because we can use two swaps to change s1 to s2: "abc" --> "bac" --> "bca".

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.