[LeetCode] 859. Buddy Strings

Problem

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

Note:

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 == null || B == null || A.length() != B.length()) return false;
        char[] s1 = A.toCharArray();
        char[] s2 = B.toCharArray();
        if (A.equals(B)) {
            int[] dict = new int[26];
            for (char ch: s1) {
                dict[ch-'a']++;
                if (dict[ch-'a'] >= 2) return true;
            }
            return false;
        }
        
        List diffIndex = new ArrayList<>();
        for (int i = 0; i < s1.length; i++) {
            if (s1[i] != s2[i]) diffIndex.add(i);
        }
        if (diffIndex.size() != 2) return false;
        int i = diffIndex.get(0), j = diffIndex.get(1);
        if (A.charAt(i) == B.charAt(j) && A.charAt(j) == B.charAt(i)) return true;
        return false;
    }
}