240306 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();

		if (command.equals("Enter") || command.equals("Change")) {
			String nickname = st.nextToken();
			nickMap.put(userId, nickname);
		}

		if (command.equals("Enter")) {
			chatLog.add(userId + "님이 들어왔습니다.");
		} else if (command.equals("Leave")) {
			chatLog.add(userId + "님이 나갔습니다.");
		}
	}

	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