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: Time Limit Exceeded)

import java.util.Scanner;

class Node
{
	int key;
	Node prev, next;

	Node()
	{
		key = -1;
		prev = next = null;
	}
}

class DoublyLinkedList
{
	Node nil;
	int N;

	DoublyLinkedList()
	{
		nil = new Node();
		nil.next = nil;
		nil.prev = nil;
		N = 0;
	}

	//先頭に挿入
	void insertNode(Node t, int val)
	{
		Node x = new Node();
		x.key = val;
		x.next = t.next;
		t.next.prev = x;
		x.prev = t;
		t.next = x;
		N++;
	}

	void insertFirst(int val)
	{
		insertNode(nil, val);
	}

	void insertLast(int val)
	{
		insertNode(nil.prev, val);
	}

	void deleteNode(Node t)
	{
		if (t == nil)
		{
			return;
		}
		t.prev.next = t.next;
		t.next.prev = t.prev;
		N--;
	}

	void deleteFirst()
	{
		deleteNode(nil.next);
	}

	void deleteLast()
	{
		deleteNode(nil.prev);
	}

	Node searchKey(int key)
	{
		Node cur = nil.next;
		while (cur != nil && cur.key != key)
		{
			cur = cur.next;
		}
		return cur;
	}

	void deleteKey(int key)
	{
		deleteNode(searchKey(key));
	}

	void print()
	{
		for (Node cur = nil.next; cur != nil; cur = cur.next)
		{
			if (cur != nil.next)
			{
				System.out.print(" ");
			}
			System.out.print(cur.key);
		}
		System.out.println();
	}
}

public class Main
{
	public static void main(String[] args)
	{
		Scanner in = new Scanner(System.in);
		DoublyLinkedList L = new DoublyLinkedList();
		int n = in.nextInt();
		for (int i = 0; i < n; ++i)
		{
			String com = in.next();
			if (com.equals("deleteFirst"))
			{
				L.deleteFirst();
			} else if (com.equals("deleteLast"))
			{
				L.deleteLast();
			} else if (com.equals("insert"))
			{
				L.insertFirst(in.nextInt());
			} else if (com.equals("delete"))
			{
				L.deleteKey(in.nextInt());
			}
		}
		L.print();
		in.close();
	}
}