[Level 2] 오픈채팅방

import java.util.*;

class Solution {
    public String[] solution(String[] record) {
        Map<String, String> map = new HashMap<>();
        List<String> list1 = new ArrayList<>();
        List<String> list2 = new ArrayList<>();
        int len = 0;
        
        for(int i=0; i<record.length; i++) {
            String[] arr =  record[i].split(" ");
            
            switch(arr[0]) {
                case "Enter":
                    list1.add(arr[1]);
                    list2.add("님이 들어왔습니다.");
                    len++;
                    map.put(arr[1], arr[2]);
                    break;
                case "Leave":
                    list1.add(arr[1]);
                    list2.add("님이 나갔습니다.");
                    len++;
                    break;
                default:
                    map.put(arr[1], arr[2]);
            }
        }
        
        String[] answer = new String[len];
        
        for(int i=0; i<answer.length; i++) { answer[i] = map.get(list1.get(i))+list2.get(i); }
        
        return answer;
    }
}