BuddyStrings.java

//859. Buddy Strings

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

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

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

        if(second==-1) return false;

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