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: Wrong Answer)

using System;
using System.Collections.Generic;

public class Program
{
  static void Main(string[] args)
  {
    int n = int.Parse( Console.ReadLine() );

    DoublyLinkedList dll = new DoublyLinkedList();
    
    for( int i = 0; i < n; i++ )
      {
        string input = Console.ReadLine();
        switch (input)
          {
          case "deleteFirst":
            dll.deleteFirst();
            break;
          case "deleteLast":
            dll.deleteLast();
            break;
          default:
            string[] inputs = input.Split(' ');
            if(inputs[0] == "insert")
              {
                dll.insert(int.Parse(inputs[1]));
              }
            else
              {
                dll.delete(int.Parse(inputs[1]));
              }
            break;
          }
      }
    dll.show();
  }
}

public class DoublyLinkedList
{
  public Node head;
  public Node tail;

  public DoublyLinkedList()
  {
    head = null;
    tail = null;
  }
  
  public void insert( int x )
  {
    Node n = new Node(x);

    if(head == null)
      {
        head = n;
        tail = n;
        n.next = null;
        n.prev = null;
      }
    else
      {
        n.next = head;
        head.prev = n;
        head = n;
        n.prev = null;
      }
  }

  public void delete( int x )
  {
    if(head == null) return;

    for(Node tp = head; tp != null; tp = tp.next)
      {
        if(tp.value == x)
          {
            if(tp == head)
              {
                deleteFirst();
              }
            else if(tp == tail)
              {
                deleteLast();
              }
            else
              {
                tp.next.prev = tp.prev;
                tp.prev.next = tp.next;
              }
          }
      }
  }

  public void deleteAll()
  {
    head = null;
    tail = null;
  }

  public void deleteFirst()
  {
    if(head == null) return;

    if(head == tail)
      {
        deleteAll(); 
      }
    else
      {
        head.next.prev = null;
        head = head.next;
      }
  }
  
  public void deleteLast()
  {
    if(head == null) return;

    if(head == tail)
      {
        deleteAll(); 
      }
    else
      {
        tail.prev.next = null;
        tail = tail.prev;
      }
  }
  
  public void show()
  {
    if (head == null) Console.WriteLine("");

    for(Node tp = head; tp != null; tp = tp.next)
      {
        if(tp == head)
          Console.Write("{0}",tp.value);
        else
          Console.Write(" {0}",tp.value);
      }
    Console.WriteLine("");
  }
}

public class Node
{
  public int value;
  public Node prev;
  public Node next;
  
  public Node(int a)
  {
    value = a;
    prev = null;
    next = null;
  }
}