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.next();
            char[] array = str.toCharArray();
            Map<Character,Integer> map = new HashMap<>();
            for(char c : array){
                if(map.containsKey(c)){
                    map.put(c,map.get(c)+1);
                }else{
                    map.put(c,1);
                }
            }
            List<Map.Entry<Character,Integer>> list = new ArrayList<>(map.entrySet());//改变封装
            //将map 转换成list 排序
            Collections.sort(list,new Comparator<Map.Entry<Character,Integer>>(){
                @Override
                public int compare(Map.Entry<Character,Integer> o1,Map.Entry<Character,Integer> o2){
                    if(o1.getValue() < o2.getValue()){
                        return 1;//返回正数说明 o1 o2 要交换
                    }else if(o1.getValue() == o2.getValue()){
                        if(o1.getKey() < o2.getKey()){
                            return -1;
                        }else{
                            return 1;
                        }
                    }else{
                        return -1;//返回负数说明 o1 o2 不要交换
                    }
                }
            });
            for(Map.Entry entry : list){//注意这里要遍历list
                System.out.print(entry.getKey());
            }
             System.out.println();
        }
    }
}