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: WA: Presentation Error)

/*
 * Created by SharpDevelop.
 * User: yog-sothoth
 * Date: 2017/02/24
 * Time: 7:12
 * 
 * To change this template use Tools | Options | Coding | Edit Standard Headers.
 */
using System;

namespace DoublyLinkedList
{
	class Program
	{
		public static void Main(string[] args)
		{
			var list=new LinkedList<int>();
			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.insertFirst(int.Parse(command[1]));
						break;
					case "delete":
						list.deletX(int.Parse(command[1]));
						break;
					case"deleteFirst":
						list.deleteFirst();
						break;
					case"deleteLast":
						list.deleteLast();
						break;
				
				}
			}
			var target=list.First;
			while(target!=list.End)
			{
				if(target.Next==list.End)
				{
					Console.Write(target.Value);
				}
				else {Console.Write(target.Value+" ");}
				target=target.Next;
			}
			
		}
	}
	
	public class Node<T>
	{
		
		
		public T Value{get;set;}
		 public Node<T> Next{get;set;}
		public Node<T> Previous{get;set;}
		
		public Node(T val,Node<T> prev, Node<T> next)
		{
			Value=val;
			Previous=prev;
			Next=next;
		}
		
	}
	public class LinkedList<T>
	{
		Node<T> dummy;
		public LinkedList()
		{
			this.dummy=new Node<T>(default(T),null,null);
			dummy.Next=dummy;
			dummy.Previous=dummy;			
		}
		public Node<T> First{get{return this.dummy.Next;}}
		public Node<T> Last{get{return this.dummy.Previous;}}
		public Node<T> End{get{return this.dummy;}}
		
		private int size=0;
		public int Count{get{return size;}}
		
		public void insertAfter(Node<T> n, T elem)
		{
			var m=new Node<T>(elem,n,n.Next);
			n.Next.Previous=m;
			n.Next=m;
			size++;
			
			
		}
		public void insertBefore(Node<T> n,T elem)
		{
			var m =new Node<T>(elem ,n.Previous,n);
			n.Previous.Next=m;
			n.Previous=m;
			size++;
		}
		
		public void insertFirst(T val)
		{
			insertAfter(dummy,val);
			
		}
		
		public Node<T> search(T val)
		{
			Node<T> target=First;
			while(target!=End)
			{
				if(target.Value.Equals(val))
				{
					return target;
				
				}
				target=target.Next;
				
			}
			return dummy;
		}
		public void deletX(T val)
		{
			Node<T> x=search(val);
			if(x!=dummy)
			{erase(x);}
			size--;
		}
		public void deleteFirst(){erase(First);
			size--;}
		public void deleteLast(){erase(Last);size--;}
		
		public void erase(Node<T> n)
		{
			n.Previous.Next=n.Next;
			n.Next.Previous=n.Previous;
		}
		
		
	}
}