题解 | #字符统计#

import java.util.Scanner;
import java.util.TreeMap;

public class Main {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        String str = scanner.next();

        //将字符存入TreeMap
        TreeMap<Character,Integer> map = new TreeMap<>();
        for(int i = 0; i < str.length(); i++){
            if(!map.containsKey(str.charAt(i))){
                map.put(str.charAt(i),1);
            }else{
                map.put(str.charAt(i),map.get(str.charAt(i)) + 1);
            }
        }

        //找到max值
        int max = 0;
        for(int ch : map.values()){
            if(max < ch){
                max = ch;
            }
        }

        //输出
        while(max != 0){
            for(char ch : map.keySet()){
                if(map.get(ch) == max){
                    System.out.print(ch);
                }
            }
            max--;
        }

    }
}