백준 JAVA 10866 덱

https://www.acmicpc.net/problem/10866

10866번: 덱

package BAEKJOON.Silver.Ⅳ;

import java.util.ArrayDeque;
import java.util.Deque;
import java.util.Scanner;

public class NO10866 {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        Deque<Integer> deque = new ArrayDeque<>();
        StringBuilder sb = new StringBuilder();

        int n = sc.nextInt();
        for (int i = 0; i < n; i++) {
            String str = sc.next();
            if(str.equals("push_back")) {
                int num = sc.nextInt();
                deque.addLast(num);
            } else if (str.equals("push_front")) {
                int num = sc.nextInt();
                deque.addFirst(num);
            }

            if(str.equals("pop_front")) {
                if(deque.isEmpty()) {
                    sb.append(-1).append("\n");
                } else {
                    sb.append(deque.pollFirst()).append("\n");
                }
            }

            if(str.equals("pop_back")) {
                if(deque.isEmpty()) {
                    sb.append(-1).append("\n");
                } else {
                    sb.append(deque.pollLast()).append("\n");
                }
            }

            if(str.equals("size")) {
                sb.append(deque.size()).append("\n");
            }

            if(str.equals("empty")) {
                if(deque.isEmpty()) {
                    sb.append(1).append("\n");
                } else {
                    sb.append(0).append("\n");
                }
            }

            if(str.equals("front")) {
                if(deque.isEmpty()) {
                    sb.append(-1).append("\n");
                } else {
                    sb.append(deque.peekFirst()).append("\n");
                }
            }

            if(str.equals("back")) {
                if(deque.isEmpty()) {
                    sb.append(-1).append("\n");
                } else {
                    sb.append(deque.peekLast()).append("\n");
                }
            }
        }
        System.out.println(sb);
    }
}