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: WA: Presentation Error)

import java.util.*;
public class Main {
	Scanner sc = new Scanner(System.in);
	Deque<Integer> List = new ArrayDeque<Integer>();
	int n;
	String order;
	int data;
	int ans;
	public void input() {
		n = sc.nextInt();
		for(int i=0; i<n; i++) {
			order = sc.next();
			if( order.equals("insert") ) {
				data = sc.nextInt();
				List.addFirst(data);
			}else if( order.equals("delete") ) {
				data = sc.nextInt();
				List.remove(data);
			}
			else if( order.equals("deleteFirst") ) {List.removeFirst();}
			else{List.removeLast();}
		}
	}
	public void output() {
		while(List.size() != 0) {
			ans = List.poll();
			if(List.size() == 0) System.out.print(ans+" \n");
			else System.out.print(ans+" ");
		}
		System.out.println();
	}
	public static void main(String[] args) {
		Main obj = new Main();
		obj.input();
		obj.output();
	}
}