题解 | #字符统计#

import java.util.Arrays;
import java.util.Scanner;
import java.util.Map;
import java.util.TreeMap;
import java.util.Collection;
import java.util.ArrayList;
import java.util.Comparator;
public class Main {
    public static void main(String[] args) {
        Scanner in = new Scanner(System.in);
        String s = in.nextLine();
        char chars[] = s.toCharArray();
        Map<Character, Integer> map = new TreeMap<>();
        for (int i = 0; i < chars.length; i++) {
            if (!map.containsKey(chars[i])) {
                map.put(chars[i], 1);
            } else {
                map.put(chars[i], map.get(chars[i]) + 1);
            }
        }
        int occurrences = 0;
        for (int i : map.values()) {
            if (occurrences < i) occurrences = i;
        }
        while (occurrences > 0) {
            for (Character c : map.keySet()) {
                if (occurrences == map.get(c)) System.out.print(c);
            }
            occurrences--;
        }

    }
}