题解 | #字符统计#

import java.util.*;

public class Main {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        String str = sc.nextLine();
        TreeMap<Character, Integer> hm = new TreeMap<>();
        char[] ch = str.toCharArray();
        for (int i = 0; i < ch.length; i++) {
            hm.put(ch[i], 0);
        }
        for (int i = 0; i < ch.length; i++) {
            hm.put(ch[i], hm.get(ch[i]) + 1);
        }
        int max = 0;
        int num = hm.size();
        for (int i = 0; i < num; i++) {
            for (char c : hm.keySet()) {
                if (hm.get(c) > max) {
                    max = hm.get(c);
                }
            }
            for(char c : hm.keySet()){
                if(hm.get(c)==max){
                    System.out.print(c);
                    hm.put(c,0);
                    max = 0;
                    break;
                }
            }
        }
    }
}