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: Memory Limit Exceeded)

import java.util.*;
 
public class Main {
 
    /**
     * @param args
     */
    public static void main(String[] args) {
        Scanner s = new Scanner(System.in);
        s.nextLine();
        ArrayDeque<Integer> seq = new  ArrayDeque<Integer>(2000000);
        String command;
        Integer num = 0;
        while(s.hasNext()){
            String input = s.nextLine();
            String[] input_array = input.split(" ");
            if(input_array.length == 1){
                command = input_array[0];
            }
            else{
                command = input_array[0];
                num = Integer.parseInt(input_array[1]);
            }
            if(command.equals("insert")){
                seq.addFirst(num);
            }
            else if(command.equals("delete")){
                seq.remove(num);
            }
            else if(command.equals("deleteFirst")){
                seq.removeFirst();
            }
            else if(command.equals("deleteLast")){
                seq.removeLast();
            }
        }
        while(seq.size() > 0){
        	if(seq.size() == 1){
                System.out.print(seq.poll() + "\n");
        	}
        	else{
                System.out.print(seq.poll() + " ");
        	}
        }
    }
}