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 C# (judge verdict: Accepted)

//?????????????????????????????????????????????
using System;

namespace DefaultNamespace
{
	/// <summary>
	/// Description of Class1.
	/// </summary>
	public class Class1
	{
		public static void Main(String[] args)
		{				
			var listA = new listArray();
			listA.start();
			listA.finish();
		}
	
	}

	public class listArray
	{
		public int first = 0;
		public int last = 0;
		public int[] list = new int[1000000];
		
		public void start()
		{
			int n = int.Parse(Console.ReadLine());
			for (int i = 0; i < n; i++) {
				string com = Console.ReadLine();
				string[] command = com.Split();
				switch (command[0]) {
					case "insert":
						list[first] = int.Parse(command[1]);//first?????¨????????????first-1????????????????????\??£?????????
						first++;
						break;
					case"deleteFirst":
						//deleteFirst();
						first--;
						while (list[first - 1] == -1) {
							first--;
						}
					
						break;
					case"deleteLast":
						//deleteLast();
						
						last++;
						while (list[last] == -1) {
							last++;
						}
						
						break;
					case "delete":
						//delete(int.Parse(command[1]));
						for (int j = first - 1; j >= last; j--) {
							if (list[j] == int.Parse(command[1])) {
								list[j] = -1;//?????????????????????-1???????????????
								while (list[first - 1] == -1) {
									first--;
								}
								while (list[last] == -1) {
									last++;
								}
								break;
							}
						}
						
						
						break;				
				}
			}
		}
		/*
		public void insert(int val)
		{
			list[first]=val;//first?????¨????????????first-1????????????????????\??£?????????
			first++;
		}
		
		public void deleteFirst()
		{
			first--;
			while(list[first-1]==-1)
			{
				first--;
			}
		}
		
		public void deleteLast()//last???????????\??£????????????
		{
			last++;
			while(list[last]==-1)
			{
				last++;
			}
		}
		
		public void delete(int val)
		{
			for(int j=first-1;j>=last;j--)
			{
				if(list[j]==val)
				{
					list[j]=-1;//?????????????????????-1???????????????
					while(list[first-1]==-1)
					{
						first--;
					}
					while(list[last]==-1)
					{
						last++;
					}
					return;
				}
			}
			return;
		}
		*/
		public void finish()
		{
			for (int k = first - 1; k > last; k--) {
				if (list[k] != -1) {
					Console.Write(list[k] + " ");
				}				
			}			
			Console.WriteLine(list[last]);	
		}
	}
}