buddy-strings.java

/*
solution to Buddy Strings at leetcode in Java.
Author : Neha Labhasetwar.
Ref : https://leetcode.com/problems/buddy-strings


Description:
Given two strings A and B of lowercase letters, return true if you can swap two letters in A so the result is equal to B, otherwise, return false.
Swapping letters is defined as taking two indices i and j (0-indexed) such that i != j and swapping the characters at A[i] and A[j]. For example, swapping at indices 0 and 2 in "abcd" results in "cbad".

Example1:
Input: A = "ab", B = "ba"
Output: true

Example2:
Input: A = "ab", B = "ab"
Output: false
*/

class Solution {
    public boolean buddyStrings(String A, String B) {
        if (A.length() != B.length()) return false;
        if (A.equals(B)) {
            int[] count = new int[26];
            for (int i = 0; i < A.length(); ++i)
                count[A.charAt(i) - 'a']++;

            for (int c: count)
                if (c > 1) return true;
            return false;
        } else {
            int first = -1, second = -1;
            for (int i = 0; i < A.length(); ++i) {
                if (A.charAt(i) != B.charAt(i)) {
                    if (first == -1)
                        first = i;
                    else if (second == -1)
                        second = i;
                    else
                        return false;
                }
            }

            return (second != -1 && A.charAt(first) == B.charAt(second) &&
                    A.charAt(second) == B.charAt(first));
        }
    }
}