Solution.txt

import java.io.*;
import java.util.*;
import java.lang.*;

public class solution
{
  public static void main(String[] args) 
    {
        // TODO Auto-generated method stub
  		Scanner sc = new Scanner(System.in);
		String s = sc.next();
		int n = s.length();
		
		String ans = frequencySort(s);
		System.out.println(ans);
    }
		    public static String frequencySort(String s) 
		   {
		    Map<Character,Integer> map =new HashMap<Character,Integer>();
		    for(int i=0;i<s.length();i++)
		    {
		        if(map.containsKey(s.charAt(i)))
		            map.put(s.charAt(i),map.get(s.charAt(i))+1);
		        else
		            map.put(s.charAt(i),1);
		    }

		    List<Map.Entry<Character,Integer>> sortedlist = new ArrayList<>(map.entrySet());
		    Collections.sort(sortedlist, new Comparator<Map.Entry<Character,Integer>>() {

		    @Override
		    public int compare(Map.Entry<Character, Integer> o1,
		            Map.Entry<Character, Integer> o2) {
		        return o2.getValue() - o1.getValue();
		    }
		    });

		    String lastString="";
		    for (Map.Entry<Character,Integer>  e : sortedlist) 
		    {
		        for(Integer j=0;j <  e.getValue();j++)
		           lastString+= e.getKey().toString();
		    }
		    return lastString;
		   }
}