题解 | #字符统计#

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.util.ArrayList;
import java.util.Scanner;

/**
 * @author eagle2020
 * @date 2021/9/29
 */
public class Main {

    public static void main(String[] args) throws IOException {
        BufferedReader reader = new BufferedReader(new InputStreamReader(System.in));
        String str;
        while((str = reader.readLine()) != null){
            int[] arr = new int[128];
            int len = str.length();
            int maxCount = 0;
            for(int i = 0; i < len; i++){
                char c = str.charAt(i);
                arr[c]++;
                if(arr[c] > maxCount){
                    maxCount = arr[c];
                }
            }

            StringBuilder sb = new StringBuilder();
            while (maxCount != 0){
                int nextCount = 0;
                for(int i = 0; i < 128; i++){
                    if(arr[i] == maxCount){
                        sb.append((char) i);
                    }
                    if(arr[i] > nextCount && arr[i] < maxCount){
                        nextCount = arr[i];
                    }
                }
                maxCount = nextCount;
            }
            System.out.println(sb);
        }


    }
}