Leetcode 859. 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

Note:

1. 0 <= A.length <= 20000
2. 0 <= B.length <= 20000
3. A and B consist only of lowercase letters.

Code (Java):

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class Solution {     public boolean buddyStrings(String A, String B) {         if (A.length() != B.length() || A.length() < 2 || B.length() < 2) {             return false;         }                   // case 1: if A == B, we only need to replace the same characters         //         if (A.equals(B)) {             int[] counts = new int[26];             for (char c : A.toCharArray()) {                 counts[c - 'a']++;                 if (counts[c - 'a'] > 1) {                     return true;                 }             }                           return false;         }                   // case 2: otherwise, we only swap once         //         int first = -1;         int second = -1;         for (int i = 0; i < A.length(); i++) {             if (A.charAt(i) != B.charAt(i)) {                 if (first == -1) {                     first = i;                 } else {                     second = i;                 }             }         }                   return A.charAt(first) == B.charAt(second) && A.charAt(second) == B.charAt(first);     } }