[アルゴリズム]標準-10866(DEX)/Java

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

class Main {
	public static void main(String args[]) throws IOException {
		BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
		StringBuilder sb = new StringBuilder();
		StringTokenizer st;
		Deque<Integer> deque = new LinkedList<Integer>();
		int N = Integer.parseInt(br.readLine());
		for (int i = 0; i < N; i++) {
			st = new StringTokenizer(br.readLine());
			String type = st.nextToken();
			switch (type) {
			case "push_front":
				deque.addFirst(Integer.parseInt(st.nextToken()));
				break;
			case "push_back":
				deque.addLast(Integer.parseInt(st.nextToken()));
				break;
			case "pop_front":
				sb.append((deque.isEmpty() ? -1 : deque.pollFirst())).append("\n");
				break;
			case "pop_back":
				sb.append((deque.isEmpty() ? -1 : deque.pollLast())).append("\n");
				break;
			case "size":
				sb.append(deque.size()).append("\n");
				break;
			case "empty":
				sb.append((deque.isEmpty() ? 1 : 0)).append("\n");
				break;
			case "front":
				sb.append((deque.isEmpty() ? -1 : deque.peekFirst())).append("\n");
				break;
			case "back":
				sb.append((deque.isEmpty() ? -1 : deque.peekLast())).append("\n");
				break;

			}
		}
		System.out.println(sb);

	}
}