src/main/java/com/fishercoder/solutions/_859.java

package com.fishercoder.solutions;

import java.util.HashSet;
import java.util.Set;

public class _859 {
    public static class Solution1 {
        public boolean buddyStrings(String A, String B) {
            if (A.length() != B.length()) {
                return false;
            }
            Character c1 = null;
            Character c2 = null;
            Set<Character> set = new HashSet<>();
            int count = 0;
            for (int i = 0; i < A.length(); i++) {
                if (A.charAt(i) != B.charAt(i)) {
                    if (count > 2) {
                        return false;
                    }
                    if (c1 == null) {
                        c1 = B.charAt(i);
                        c2 = A.charAt(i);
                        count++;
                        continue;
                    }
                    if (c1 != A.charAt(i) || c2 != B.charAt(i)) {
                        return false;
                    }
                    count++;
                }
                set.add(A.charAt(i));
            }
            return count == 2 || (count == 0 && set.size() < A.length());
        }
    }
}