[프로그래머스/Java] 정수 내림차순으로 배치하기

-Code

import java.util.*;

class Solution {
    public long solution(long n) {
        ArrayList<Long> arr = new ArrayList<>();
        while (n > 0) {
            arr.add(n % 10);
            n /= 10;
        }
        arr.sort(Collections.reverseOrder());

        StringBuilder answer = new StringBuilder();
        for (Long num : arr) answer.append(num);

        return Long.parseLong(answer.toString());
    }
}