오픈채팅방

package prog;

import java.util.ArrayList;
import java.util.Arrays;
import java.util.HashMap;

import java.util.StringTokenizer;

public class 오픈채팅방 {
    public static void main(String[] args) {
        Solution_오픈채팅방 s = new Solution_오픈채팅방();
        String[] result;
        result = s.solution(new String[] {"Enter uid123 uid1234", "Leave uid1234", "Enter uid4567 uid123", "Change uid4567 uid1234", "Leave uid4567"});
        result = s.solution(new String[] {"Enter uid1234 Muzi", "Enter uid4567 Prodo","Leave uid1234","Enter uid1234 Prodo","Change uid4567 Ryan"});
        System.out.println("Arrays.toString(result) = " + Arrays.toString(result));
    }

}

class Solution_오픈채팅방{
    public String[] solution(String[] record) {
        String[] answer = {};

        HashMap<String,String> map= new HashMap<>();
        StringTokenizer st;

        for (int i = record.length-1; i >= 0; i--) {
            st = new StringTokenizer(record[i]," ");
            String action = st.nextToken();
            if(action.equals("Enter") || action.equals("Change")){
                String uid = st.nextToken();
                if(!map.containsKey(uid)){
                    map.put(uid,st.nextToken());
                }
            }

        }
        ArrayList<String> tmpAnswer = new ArrayList<>();
        for (int i = 0; i < record.length; i++) {
            st = new StringTokenizer(record[i]," ");
            String action = st.nextToken();
            if(action.equals("Enter")){
                tmpAnswer.add(map.get(st.nextToken())+"님이 들어왔습니다.");
            }
            else if(action.equals("Leave")){
                tmpAnswer.add(map.get(st.nextToken())+"님이 나갔습니다.");
            }

        }
        answer = new String[tmpAnswer.size()];
        for (int i = 0; i < tmpAnswer.size(); i++) {
            answer[i] = tmpAnswer.get(i);
        }
        return answer;
    }
}