K-Similar Strings

Strings A and B are K-similar (for some non-negative integer K) if we can swap the positions of two letters in A exactly K times so that the resulting string equals B.

Given two anagrams A and B, return the smallest K for which A and B are K-similar.

Example 1:

Input: A = "ab", B = "ba"
Output: 1

Example 2:

Input: A = "abc", B = "bca"
Output: 2

Example 3:

Input: A = "abac", B = "baca"
Output: 2

Example 4:

Input: A = "aabc", B = "abca"
Output: 2

Note:

1. 1 <= A.length == B.length <= 20

2. A and B contain only lowercase letters from the set {'a', 'b', 'c', 'd', 'e', 'f'}

class Solution {
    public int kSimilarity(String A, String B) {
        char[] strB = B.toCharArray();
        Queue<String> q = new LinkedList<>();
        q.add(A);
        int count = 0;
        while (q.size() != 0) {
            int size = q.size();
            while (size-- > 0) {
                char[] node = q.poll().toCharArray();
                int i = 0;
                while (i < strB.length && node[i] == strB[i])
                    i++;
                // If found match
                if (i == strB.length)
                    return count;
                for (int j = i + 1; j < node.length; j++) {
                    if (node[j] == strB[i]) {
                        swap(node, i, j);
                        q.add(new String(node));
                        swap(node, i, j);
                    }
                }
            }
            count++;
        }
        return -1;
    }

    public void swap(char[] str, int i, int j) {
        char t = str[i];
        str[i] = str[j];
        str[j] = t;
    }
}