백준 11723번(Java)

import java.io.*;
import java.util.*;

public class Main {

	public static void main(String[] args) throws IOException {
		BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
		StringBuilder sb = new StringBuilder();
		
		int M = Integer.parseInt(br.readLine());
		Set<Integer> set = new HashSet<>();
		
		for(int i=0; i<M; i++) {
			StringTokenizer st = new StringTokenizer(br.readLine());
			String command = st.nextToken();
			int input = -1;
			
			switch(command) {
			case "add":		set.add(Integer.parseInt(st.nextToken())); break;
			case "remove":	set.remove(Integer.parseInt(st.nextToken())); break;
			case "check":	input = Integer.parseInt(st.nextToken()); 
							if(set.contains(input)) {
								sb.append(1);
							} else {
								sb.append(0);
							}
							sb.append('\n');
							break;
			case "toggle": 	input = Integer.parseInt(st.nextToken());
							if(set.contains(input)) {
								set.remove(input);
							} else {
								set.add(input);
							}
							break;
			case "all": 	set = new HashSet<>();
							for(int j=1; j<=20; j++) {
								set.add(j);
							}
							break;
			case "empty": 	set.clear(); break;
			}
		}
		System.out.println(sb);
	}
}