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.Collections.Generic;
using System.Linq;
using System.Text;

namespace ConsoleApplication1
{
    class Program
    {
        static void Main(string[] args)
        {
            LinkedList dll = new LinkedList();

            int n = int.Parse(Console.ReadLine());

            for (int i = 0; i < n; i++)
            {
                string[] input = Console.ReadLine().Split(' ');

                switch (input[0])
                {
                    case "insert":
                        dll.Insert(input[1]);
                        break;
                    case "delete":
                        Node temp = dll.Search(input[1]);
                        dll.Erace(temp);
                        break;
                    case "deleteFirst":
                        dll.Erace(dll.first);
                        break;
                    case "deleteLast":
                        dll.Erace(dll.last);
                        break;
                }
            }

            StringBuilder sb = new StringBuilder();

            for (Node node = dll.first; node != dll.end; node = node.next)
            {
                sb.Append(" " + node.val);
            }
            Console.WriteLine(sb.ToString().TrimStart());
        }
    }

    class Node
    {
        internal string val;
        internal Node prev;
        internal Node next;

        internal Node(string val, Node prev, Node next)
        {
            this.val = val;
            this.prev = prev;
            this.next = next;
        }
    }

    class LinkedList
    {
        Node dummy;

        public Node first { get { return dummy.next; } }
        public Node last { get { return dummy.prev; } }
        public Node end { get { return dummy; } }

        public LinkedList()
        {
            dummy = new Node(null, null, null);
            dummy.next = dummy;
            dummy.prev = dummy;
        }

        public void Insert(string val)
        {
            Node temp = new Node(val, dummy, dummy.next);
            dummy.next.prev = temp;
            dummy.next = temp;
        }

        public Node Search(string val)
        {
            Node ret = dummy.next;

            while (ret.val != val && ret != end)
            {
                ret = ret.next;
            }

            return ret;
        }

        public Node Erace(Node node)
        {
            if (node == dummy)
            {
                return dummy;
            }

            node.prev.next = node.next;
            node.next.prev = node.prev;

            return node.next;
        }
    }
}