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: Accepted)

import java.io.PrintWriter;
import java.util.ArrayDeque;
import java.util.Scanner;

public class Main {

	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);

		int n = sc.nextInt();
		ArrayDeque<Long> list = new ArrayDeque<>();
		long ele = 0;

		for (int i = 0; i < n; i++) {
			switch (sc.next()) {
			case "insert":
				ele = Integer.parseInt(sc.next());
				list.offerFirst(ele);
				break;
			case "delete":
				ele = Long.parseLong(sc.next());
				list.remove(ele);
				break;
			case "deleteFirst":
				list.pollFirst();
				break;
			case "deleteLast":
				list.pollLast();
				break;
			}
		}

		PrintWriter out = new PrintWriter(System.out);

		for (int i = 0; i < list.size();) {
			out.print(list.pollFirst());
			out.print(list.size() == 0 ? "" : " ");
		}
		out.println();
		out.flush();
	}
}