Method isDuplicate

Java/buddy-strings.java:10–20

(String str)

*/
class Solution {
    public boolean isDuplicate(String str){
        int[] fre = new int[26];
        for(int i=0; i<str.length(); i++){
            int ind = str.charAt(i) - 'a';
            fre[ind]++;
            if(fre[ind] > 1){
                return true;
            }
        }
        return false;
    }
    public boolean buddyStrings(String A, String B) {
        if(A.length() != B.length()){
            return false;