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.Scanner;
import java.util.Arrays;
import java.util.Deque;
import java.util.ArrayDeque;


class Main{
	public static void main(String[] args)throws Exception{
		Scanner scanner = new Scanner(System.in);
		Deque<Integer> stack = new ArrayDeque<>();
		int n = Integer.parseInt(scanner.nextLine());
		StringBuilder sb = new StringBuilder();
		
		for(int i = 0; i < n; i++){
			String command = scanner.next();
			if(command.equals("insert")){
				stack.offerFirst(scanner.nextInt());
			}else if(command.equals("delete")){
				stack.remove(scanner.nextInt());
			}else if(command.equals("deleteFirst")){
				stack.removeFirst();
			}else{
				stack.removeLast();
			}
			
			if(i != n-1){
				String nothing = scanner.nextLine();
			}
		}

		sb.append(String.valueOf(stack.poll()));
		for(int num: stack){
		    sb.append(" ");
		    sb.append(String.valueOf(stack.poll()));
		}
		
		System.out.println(sb);

	}
}