UVA - 11577 - Letter Frequency

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;

public class Main {

    public static void main(String[] args) throws IOException {
        InputStreamReader isr = new InputStreamReader(System.in);
        BufferedReader br = new BufferedReader(isr);
        StringBuffer sb = new StringBuffer("");
        String m="";
        int cases=Integer.parseInt(br.readLine());
        for(int i=0;i<cases;i++) {
            int[] arr=new int[26];
            m=br.readLine().toLowerCase();
            int max=-1;
            for(int j=0;j<m.length();j++){
                if(m.charAt(j)>='a' &&m.charAt(j)<='z' ){
                    arr[m.charAt(j)-97]++;
                    if(arr[m.charAt(j)-97]>max)
                        max=arr[m.charAt(j)-97];
                }
            }
             for(int j=0;j<26;j++){
                 if(arr[j]==max){
                     sb.append((char)(j+97));
                 }
             }
            sb.append("\n");
        }
        System.out.print(sb);
    } 
}