230619 오픈채팅방

public String[] solution(String[] record) {
	List<String> chatLog = new ArrayList<>();
	Map<String, String> nickMap = new HashMap<>();

	for (String log : record) {
		StringTokenizer st = new StringTokenizer(log);
		String command = st.nextToken();
		String userId = st.nextToken();
		String nickname = "";

		if (!command.equals("Leave")) {
			nickname = st.nextToken();
		}

		switch (command) {
			case "Enter":
				nickMap.put(userId, nickname);
				chatLog.add(userId + "님이 들어왔습니다.");
				break;
			case "Leave":
				chatLog.add(userId + "님이 나갔습니다.");
				break;
			case "Change":
				nickMap.put(userId, nickname);
				break;
			default:
				break;
		}
	}

	String[] answer = new String[chatLog.size()];
	int logIdx = 0;

	for (String str : chatLog) {
		int endOfId = str.indexOf("님");
		String userId = str.substring(0, endOfId);

		answer[logIdx++] = str.replace(userId, nickMap.get(userId));
	}

	return answer;
}

출처:https://school.programmers.co.kr/learn/courses/30/lessons/42888