백준 11723번 (출력은 StringBuilder)

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.util.*;

// Press Shift twice to open the Search Everywhere dialog and type show whitespaces,
// then press Enter. You can now see whitespace characters in your code.
public class Main {
public static void main(String[] args) throws IOException {

    BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
    StringBuilder sb = new StringBuilder();
    int x = Integer.parseInt(br.readLine());


    Set set = new HashSet();


    for (int i = 0; i < x; i++) {
        StringTokenizer st = new StringTokenizer(br.readLine());
        String method = st.nextToken();




        if(method.equals("add"))
        {
            int count = Integer.parseInt(st.nextToken());
            set.add(count);
        }
        if(method.equals("check"))
        {
            int count = Integer.parseInt(st.nextToken());
            if(set.contains(count))
            {
                sb.append("1\n");
            }
            else{
                sb.append("0\n");
            }
        }
        if(method.equals("remove"))
        {
            int count = Integer.parseInt(st.nextToken());
            set.remove(count);
        }
        if(method.equals("toggle"))
        {
            int count = Integer.parseInt(st.nextToken());
            if(set.contains(count))
            {
                set.remove(count);
            }
            else{
                set.add(count);
            }
        }
        if(method.equals("all"))
        {
            for (int j = 1; j <= 20 ; j++) {
                set.add(j);
            }
        }
        if(method.equals("empty"))
        {
            set.clear();
        }




    }
    System.out.println(sb);






}

} 출력은 확실히 StringBuilder을 이용해야지 시간 초과가 발생하지 않는 것 같다.