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;
using System.Threading.Tasks;

namespace _1_3_C_DoublyLinkedList
{
    class Program
    {
        static void Main(string[] args)
        {
            var n = int.Parse(Console.ReadLine());
            var linkedList = new LinkedList<int>();
            for (int i = 0; i < n; i++)
            {
                var input = Console.ReadLine().Split(' ');
                int num = 0;
                var command = input[0];
                if (input.Length > 1)
                {
                    num = int.Parse(input[1]);
                }

                switch (command)
                {
                    case "insert":
                        linkedList = Insert(linkedList, num);
                        continue;

                    case "delete":
                        linkedList = Delete(linkedList, num);
                        continue;

                    case "deleteFirst":
                        linkedList = DeleteFirst(linkedList);
                        continue;

                    case "deleteLast":
                        linkedList = DeleteLast(linkedList);
                        continue;
                }
            }
            Console.WriteLine(string.Join(" ",linkedList));
        }

        public static LinkedList<int> Insert(LinkedList<int> list, int num)
        {
            list.AddFirst(num);
            return list;
        }

        public static LinkedList<int> Delete(LinkedList<int> list, int num)
        {
            var deleteIndex = list.Find(num);
            if (deleteIndex == null)
            {
                return list;
            }
            list.Remove(deleteIndex);
            return list;
        }

        public static LinkedList<int> DeleteFirst(LinkedList<int> list)
        {
            list.RemoveFirst();
            return list;
        }

        public static LinkedList<int> DeleteLast(LinkedList<int> list)
        {
            list.RemoveLast();
            return list;
        }
    }
}