https://school.programmers.co.kr/learn/courses/30/lessons/64063

제출 코드

import java.util.HashMap;
import java.util.Map;

class Solution {
    Map<Long, Long> map = new HashMap<>();
    public long[] solution(long k, long[] room_number) {
        long[] answer = new long[room_number.length];
        for (int i = 0; i < room_number.length; i++) {
            answer[i] = findEmptyRoom(room_number[i]);
        }
        return answer;
    }
    long findEmptyRoom(long room) {
        if (!map.containsKey(room)) {
            map.put(room, room + 1);
            return room;
        }
        long next = map.get(room);
        long empty = findEmptyRoom(next);
        map.put(room, empty);
        return empty;
    }
}