题解 | #字符统计#

import java.util.*;

public class Main {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        while (sc.hasNext()) {
            String str = sc.nextLine();
            Map<Character, Integer> map = new HashMap<>();
            for (char c : str.toCharArray()) {
                map.put(c, map.getOrDefault(c, 0) + 1);
            }
            ArrayList<Map.Entry<Character, Integer>> list = new ArrayList<>(map.entrySet());
            list.sort(new MyComparator());
            for (Map.Entry<Character, Integer> entry : list) {
                System.out.print(entry.getKey());
            }
        }
        sc.close();
    }

    private static class MyComparator implements Comparator<Map.Entry<Character, Integer>> {
        @Override
        public int compare(Map.Entry<Character, Integer> o1, Map.Entry<Character, Integer> o2) {
            if (Objects.equals(o1.getValue(), o2.getValue())) {
                return o1.getKey().compareTo(o2.getKey());
            } else {
                return o2.getValue().compareTo(o1.getValue());
            }
        }
    }
}