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 JAVA (judge verdict: Time Limit Exceeded)

import java.io.*;
import java.util.*;

public class Main
{
    public static void main(String[] args)
    {
        LinkedList<Integer> list = new LinkedList<Integer>();
        Scanner scan = new Scanner(System.in);
        int hash = 20000000;
        int n = scan.nextInt();
        int memory[] = new int[hash];
        int num;
        for(int i=0; i<n; i++)
        {
            String command = scan.next();
            switch(command)
            {
                case "insert":
                    num=scan.nextInt();
                    memory[num%hash]++;
                    list.offerFirst(num);
                    break;
                case "delete":
                    num=scan.nextInt();
                    if(memory[num%hash]>0)
                    {
                        list.remove((Integer)num);
                        memory[num%hash]--;
                    }
                    break;
                case "deleteFirst":
                    memory[list.getFirst()%hash]--;
                    list.pollFirst();
                    break;
                case "deleteLast":
                    memory[list.getLast()%hash]--;
                    list.pollLast();
                    break;
                default:
                    break;
            }
        }
        while(list.size()>1)
        {
            System.out.printf("%d ",list.poll());
        }
        System.out.println(list.poll());
    }
}