[백준] 10845번 큐

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.util.Deque;
import java.util.LinkedList;
import java.util.StringTokenizer;
public class Main {

    public static void main(String[] args) throws NumberFormatException, IOException {
    	BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
    	
    	int n = Integer.parseInt(br.readLine());
    	
    	StringBuilder sb = new StringBuilder();
    	Deque<Integer> queue = new LinkedList<>();
    	
    	for(int i=0; i<n; i++) {
    		StringTokenizer st = new StringTokenizer(br.readLine());
    		String order = st.nextToken();
    		int addNumber = 0;
    		switch(order) {
    		
    		case "push":
    			addNumber = Integer.parseInt(st.nextToken());
    			queue.add(addNumber);
    			break;
    			
    		case "pop":
    			if(queue.isEmpty()) sb.append("-1").append('\n');
    			else {
    				sb.append(queue.remove()).append('\n');
    			}
    			break;
    			
    		case "size":
    			sb.append(queue.size()).append('\n');
    			break;
    		
    		case "empty":
    			if(queue.isEmpty()) sb.append("1").append('\n');
    			else {
    				sb.append("0").append('\n');
    			}
    			break;
    			
    		case "front":
    			if(queue.isEmpty()) sb.append("-1").append('\n');
    			else {
    				sb.append(queue.peek()).append('\n');
    			}
    			break;
    			
    		case "back":
    			if(queue.isEmpty()) sb.append("-1").append('\n');
    			else {
    				sb.append(queue.peekLast()).append('\n');
    			}
    			break;

    		}
    	}
    	
    	System.out.println(sb.toString());

    }
}