https://www.acmicpc.net/problem/1427
import java.util.ArrayList;
import java.util.Collections;
import java.util.Comparator;
import java.util.Scanner;
public class B1427 {
public static void main(String[] args) {
// TODO Auto-generated method stub
Scanner sc= new Scanner(System.in);
int num = sc.nextInt();
ArrayList<Integer> arr = new ArrayList<>();
// 각 자리를 나눠 List에 저장
int remain;
do {
remain = num % 10;
num = num / 10;
arr.add(remain);
}
while (num > 0);
// 내림차순으로 Sort
Collections.sort(arr, Comparator.reverseOrder());
for(int i:arr) {
System.out.print(i);
}
}
}