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;
using System.Text;

class Program
{

    public class Node
    {
        public static Node First = null;
        public static Node Last = null;
        public int Number;
        public Node Prev = null;
        public Node Next = null;

        public void Delete()
        {
            if(this.Prev != null)
            {
                this.Prev.Next = this.Next; 
            } else
            {
                First = this.Next;
            }
            if(this.Next != null)
            {
                this.Next.Prev = this.Prev;
            } else
            {
                Last = this.Prev;
            }
        }

        public void Add()
        {
            if(First == null)
            {
                First = this;
                Last = this;
            } else
            {
                First.Prev = this;
                this.Next = First;
                First = this;
            }
        }


    }
    public void Proc()
    {
        int commandCount = int.Parse(Console.ReadLine());
        for(int i=0; i<commandCount; i++)
        {
            string[] inpt = Console.ReadLine().Split(' ');
            int num = 0;
            if(inpt.Length > 1)
            {
                num = int.Parse(inpt[1]);
            }

            switch(inpt[0])
            {
                case "insert":
                    Node nd = new Node();
                    nd.Number = num;
                    nd.Add();
                    break;
                case "delete":
                    Node n = Node.First;
                    while(n != null)
                    {
                        if(n.Number == num)
                        {
                            n.Delete();
                            break;
                        } else
                        {
                            n = n.Next;
                        }
                    }
                    break;
                case "deleteFirst":
                    Node.First.Delete();
                    break;
                case "deleteLast":
                    Node.Last.Delete();
                    break;
            }
        }
        StringBuilder ans = new StringBuilder();
        Node node = Node.First;
        while (node != null)
        {
            if (ans.Length > 0)
            {
                ans.Append(" ");
            }
            ans.Append(node.Number);
            node = node.Next;
        }

        Console.WriteLine(ans.ToString());

    }

    static void Main(string[] args)

    {

        Program prg = new Program();
        prg.Proc();

    }
}