BuddyStrings.java

package LeetcodePractice;

public class BuddyStrings {
    public static boolean buddyStrings(String s, String goal) {
        if (s.length() != goal.length()) return false;

    
        if (s.equals(goal)) {
            int[] count = new int[26];
            for (char c : s.toCharArray()) {
                count[c - 'a']++;
                if (count[c - 'a'] > 1) return true; 
            }
            return false;
        }

        
        int first = -1, second = -1, diffCount = 0;
        for (int i = 0; i < s.length(); i++) {
            if (s.charAt(i) != goal.charAt(i)) {
                diffCount++;
                if (first == -1) first = i;
                else second = i;
            }
        }

       
        return diffCount == 2 &&
               s.charAt(first) == goal.charAt(second) &&
               s.charAt(second) == goal.charAt(first);
    }

    public static void main(String[] args) {
        System.out.println(buddyStrings("ab", "ba"));
        System.out.println(buddyStrings("ab", "ab")); 
        System.out.println(buddyStrings("aa", "aa")); 
    }
}