Buddy Strings

Given two strings A and B of lowercase letters, return true if and only if we can swap two letters in A so that the result equals B.

Example 1:

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

Example 2:

Input: A = "ab", B = "ab"
Output: false

Example 3:

Input: A = "aa", B = "aa"
Output: true

Example 4:

Input: A = "aaaaaaabc", B = "aaaaaaacb"
Output: true

Example 5:

Input: A = "", B = "aa"
Output: false

Constraints:

0 <= A.length <= 20000
0 <= B.length <= 20000
A and B consist only of lowercase letters.

Solution:

class Solution {
    public boolean buddyStrings(String A, String B) {
        if (A.length() != B.length()) {
            return false;
        }
        int[] chars = new int[26];
        boolean repeat = false;
        Map<Character, Character> map = new HashMap();
        for (int i = 0; i < A.length(); i ++) {
            char a = A.charAt(i);
            char b = B.charAt(i);
            chars[a - 'a'] ++;
            if (chars[a - 'a'] > 1) {
                repeat = true;
            }
            if (a == b) {
                continue;
            }
            if (map.size() >= 2) {
                return false;
            } else if (map.size() == 1) {
                if (map.containsKey(b)) {
                    if (map.get(b) == a) {
                        map.put(a, b);
                        continue;
                    }
                }
                return false;
            } else {
                map.put(a, b);
            }
        }
        return map.size() == 2 || (repeat && map.size() == 0);
    }
}