オープンチャットルーム

import java.util.*;
class Solution {
    public String[] solution(String[] record) {
       Map<String, String> idmap = new HashMap<String, String>();
       ArrayList<String> arr = new ArrayList<String>();
       for(String str : record){
          String[] line = str.split(" ");
          if(line[0].equals("Enter") || line[0].equals("Change")){
              idmap.put(line[1],line[2]);
          }
       }
        for(String str : record){
            String[] line = str.split(" ");
            if(line[0].equals("Enter")){
                arr.add(idmap.get(line[1])+"님이 들어왔습니다.");
            }else if(line[0].equals("Leave")){
                arr.add(idmap.get(line[1])+"님이 나갔습니다.");
            }
        }
        String[] answer = new String[arr.size()];
        arr.toArray(answer);
        
        return answer;
    }
}

		1. Arrays.asList()

List<String> list = new ArrayList<>(Arrays.asList(arr));

		2. Collectors.toList()

String[] arr = { "A", "B", "C" };
// 배열 -> List로 변환
List<String> list = Stream.of(arr).collect(Collectors.toList());