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;

namespace ALDS1_3_C
{
    class Program
    {
        static int[] S = new int[2000000];

        static int top;
        static int last;

        static void Main(string[] args)
        {
            int n = getint("a");
            for (int i = 0; i < n; i++)
            {
                string[] d = getsplit();
                if (d[0] == "insert")
                {
                    insert(getint(d[1])); 
                }
                else if (d[0] == "delete")
                {
                    delete(getint(d[1]));
                }
                else if(d[0] == "deleteFirst" )
                {
                    deleteFirst();
                }
                else
                {
                    deleteLast();
                }
            }

            int a = 0;
            for (int i = top; i >= last; i--)
            {
                if (S[i] != 0 && a==1)
                {
                    Console.Write(" "+ (S[i] - 1));
                }
                else if (S[i] != 0)
                {
                    Console.Write(S[i] - 1);
                    a = 1;
                }               
            }
            Console.WriteLine();
        }

        public static string[] getsplit()
        {
            string[] x = Console.ReadLine().Split(' ');
            return x;
        }
        public static int getint(string a)
        {

            if (a == "a")
            {
                int x = int.Parse(Console.ReadLine());
                return x;
            }
            else
            {
                int x = int.Parse(a);
                return x;
            }
        }

        static void insert(int x)
        {
            S[top] = x+1;
            top++;
        }

        static void delete(int x)
        {
            for (int i = top - 1; i >= last; i--)
            {
                if (S[i] == x+1)
                {
                    S[i] = 0;
                    break;
                }
            }
        }

        static void deleteFirst()
        {
            while (S[top - 1] == 0) top--;
           
            S[top - 1] = 0;
            top--;
        }
        static void deleteLast()
        {
            while (S[last] == 0) last++;
            S[last] = 0;
            last++;
        }

    }
}