Problem:
Doubly Linked List

Your task is to implement a double linked list.

Write a program which performs the following operations:

insert x: insert an element with key x into the front of the list.

delete x: delete the first element which has the key of x from the list. If there is not such element, you need not do anything.

deleteFirst: delete the first element from the list.

deleteLast: delete the last element from the list.

Input

The input is given in the following format:

n

command1

command2

...

commandn

In the first line, the number of operations n is given. In the following n lines, the above mentioned operations are given in the following format:

insert x

delete x

deleteFirst

deleteLast

Output

Print all the element (key) in the list after the given operations. Two consequtive keys should be separated by a single space.

Constraints

The number of operations ≤ 2,000,000

The number of delete operations ≤ 20

0 ≤ value of a key ≤ 109

The number of elements in the list does not exceed 106

For a delete, deleteFirst or deleteLast operation, there is at least one element in the list.

Sample Input 1

7
insert 5
insert 2
insert 3
insert 1
delete 3
insert 6
delete 5

Sample Output 1

6 1 2

Sample Input 2

9
insert 5
insert 2
insert 3
insert 1
delete 3
insert 6
delete 5
deleteFirst
deleteLast

Sample Output 2

1

Solution in JAVA (judge verdict: Memory Limit Exceeded)

import java.util.LinkedList;
import java.util.Scanner;

/**
 * ZAKIREN第5章
 *
 * @author K.Yamauchi
 *
 */
public class Main {

	/** 入力用 */
	private static Scanner scan = new Scanner(System.in);

	/** 出力用 */
//	private static StringBuilder stringBuilder = new StringBuilder();

	/**
	 * メイン。
	 * @param args
	 */
	public static void main(String[] args) {

		// １行目の読み込み
		int commandNum = Integer.parseInt(scan.nextLine());

		// 2行目以降（プロセスとクオンタム）の読み込み
		String[] commands = new String[commandNum];
		for (int i = 0; i < commandNum; i++) {
			commands[i] = scan.nextLine();
		}

		// 読み込み終了
		scan.close();
		scan = null;

		// 計算を実行
		LinkedList<Integer> list = execution(commandNum, commands);

		// 結果出力
		for (int i = 0, size = list.size(); i < size; i++) {
			System.out.print(list.poll() + (i < size - 1 ? " " : "\n"));
		}

	}

	/**
	 *
	 * @param commandNum
	 * @param commands
	 */
	private static LinkedList<Integer> execution(int commandNum, String[] commands) {

		// 計算用リスト
		LinkedList<Integer> linkedList = new LinkedList<>();

		// キューの中身がなくなるまで計算
		for (int i = 0; i < commandNum; i++) {
			// コマンドを一つ取得
			String[] command = commands[i].split(" ");

			// コマンドごとの処理を実行
			if (command[0].equals("insert")) {
				linkedList.push(Integer.parseInt(command[1]));
			} else if (command[0].equals("delete")) {
				int index = linkedList.indexOf(Integer.parseInt(command[1]));
				if (index >= 0) {
					linkedList.remove(index);
				}
			} else if (command[0].equals("deleteFirst")) {
				linkedList.removeFirst();
			} else if (command[0].equals("deleteLast")) {
				linkedList.removeLast();
			}
		}

		return linkedList;

	}

}