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 {
	public static void main(String[] args) {
		LinkedList<Integer> list = new LinkedList<Integer>();
		Scanner scanner = new Scanner(System.in);
		
		long n = scanner.nextLong();
		scanner.nextLine();
		
		for (long i = 0; i < n; i ++) {
			String command = scanner.nextLine();
			if (command.substring(0,7).intern().equals("insert ")){
				Integer x = Integer.valueOf(command.substring(7).intern());
				list.addFirst(x);
			} else if (command.substring(0,7).intern().equals("delete ")) {
				Integer x = Integer.valueOf(command.substring(7).intern());
				list.remove(x);
			} else if (command.equals("deleteFirst")) {
				list.remove();
			} else {
				list.removeLast();
			}
		}
		
		scanner.close();
		
		for (int i = 0; i < list.size() - 1; i++) {
			System.out.print(list.get(i) + " ");
		}
		System.out.println(list.getLast());
	}
}