230309 호텔 방 배정

public long[] solution(long k, long[] room_number) {
    Map<Long, Long> nextRooms = new HashMap<>();
    long[] answer = new long[room_number.length];

    for (int i = 0; i < room_number.length; i++) {
        long emptyRoom = findEmptyRoom(room_number[i], nextRooms);
        answer[i] = emptyRoom;
        nextRooms.put(room_number[i], emptyRoom + 1);
    }

    return answer;
}

private long findEmptyRoom(long request, Map<Long, Long> nextRooms) {
    if (!nextRooms.containsKey(request)) {
        nextRooms.put(request, request + 1);
        return request;
    }

    long emptyRoom = findEmptyRoom(nextRooms.get(request), nextRooms);
    nextRooms.put(request, emptyRoom);
    return emptyRoom;
}