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;

namespace AizuOnlineJudge
{
    class Program
    {
        static void Main(string[] args)
        {
            var list = new DoublyLinkedList();

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

            for(var i = 0; i < n; ++i)
            {
                var ops = Console.ReadLine().Split(' ');
                switch(ops[0])
                {
                    case "insert":
                        list.Insert(int.Parse(ops[1]));
                        break;
                    case "delete":
                        list.Delete(int.Parse(ops[1]));
                        break;
                    case "deleteFirst":
                        list.DeleteFirst();
                        break;
                    case "deleteLast":
                        list.DeleteLast();
                        break;
                }
            }
            list.Print();
        }
    }

    internal class DoublyLinkedList
    {
        private int[] _list = new int[2000000];
        private int First { set; get; }
        private int Last { set; get; }

        public DoublyLinkedList()
        {
            First = _list.Length;
            Last = _list.Length - 1;
        }

        internal void Insert(int v)
        {
            First--;
            _list[First] = v;
        }

        internal void Delete(int v)
        {
            if (_list[First] == v)
            {
                DeleteFirst(); return;
            }
            for(var i = First + 1; i <= Last; ++i)
            {
                if(_list[i] == v)
                {
                    _list[i] = -1;
                    if (i == Last) DeleteLast();
                    break;
                }
            }
        }

        internal void DeleteFirst()
        {
            First++;
        }

        internal void DeleteLast()
        {
            Last--;
        }

        public void Print()
        {
            var isOut = false;
            for(var i = First; i <= Last; ++i)
            {
                var v = _list[i];
                if (v >= 0)
                {
                    if (isOut) Console.Write(" ");
                    Console.Write(v);
                    isOut = true;
                }
            }
            Console.WriteLine();
        }
    }
}