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.IO;
using System.Linq;
using static System.Console;

namespace DoubleyLinkedList
{
    internal class Program
    {
        public static void Main(string[] args)
        {
            var n = int.Parse(ReadLine());
            var d_list = new DoubleLinkedList<int>();
            for (var i = 0; i < n; i++)
            {
                var command = ReadLine().Split(' ');
                switch (command[0])
                {
                    case "insert":
                        d_list.Insert(int.Parse(command[1]));
                        break;
                    case "delete":
                        d_list.Delete(int.Parse(command[1]));
                        break;
                    case "deleteFirst":
                        d_list.DeleteFirst();
                        break;
                    case "deleteLast":
                        d_list.DeleteLast();
                        break;
                }
            }

            var sw = new StreamWriter(OpenStandardOutput()) {AutoFlush = false};
            SetOut(sw);
            var result = new List<int>();
            for (var i = d_list.First; i != d_list.End; i = i.Next)
            {
                result.Add(i.Value);
            }
            WriteLine(string.Join(" ",result).Trim());
            Out.Flush();

        }
    }

    public class Node<T>
    {
        private Node<T> prev;
        private Node<T> next;

        internal Node(T val, Node<T> prev, Node<T> next)
        {
            this.Value = val;
            this.prev = prev;
            this.next = next;
        }

        public T Value { get; }

        public Node<T> Previous
        {
            get { return prev; }
            set { prev = value; }
        }

        public Node<T> Next
        {
            get { return next; }
            set { next = value; }
        }
    }

    public class DoubleLinkedList<T> where T : IComparable
    {
        public DoubleLinkedList()
        {
            End = new Node<T>(default(T), null, null);
            End.Next = End;
            End.Previous = End;
        }

        public Node<T> First
        {
            get { return End.Next; }
        }

        private Node<T> Last 
        {
            get { return End.Previous; }
        }

        public Node<T> End { get; }

        public Node<T> Insert(T elem)
        {
            var node = new Node<T>(elem, End, End.Next);
            End.Next.Previous = node;
            End.Next = node;
            return node;
        }

        private Node<T> Erase(Node<T> n)
        {
            n.Previous.Next = n.Next;
            n.Next.Previous = n.Previous;
            return n.Next;           
        }
        public Node<T> Delete(T elem)
        {
            var n = Search(elem);
            return n == null ? null : Erase(n);
        }

        public Node<T> DeleteFirst()
        {
            return Erase(First);
        }

        public Node<T> DeleteLast()
        {
            return Erase(Last);
        }

        private Node<T> Search(T elem)
        {
             for (var i = First; i != End; i = i.Next)
            {
                if (elem.CompareTo(i.Value) == 0)
                {
                    return i;
                }
            }

            return null;
        }
    }
}