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: Time Limit Exceeded)

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

public class Main {
	void run() {
		Scanner sc = new Scanner(System.in);
		Deque<Integer> Q = new ArrayDeque<>(2000000);
		int n = sc.nextInt();
		for(int i = 0; i < n; i++) {
			String s = sc.next();
			int a;
			if(s.equals("insert")) {
				a = sc.nextInt();
				Q.addFirst(a);
			}
			else if(s.equals("delete")) {
				a = sc.nextInt();
				Q.remove(a);
			}
			else if(s.equals("deleteFirst")) {
				Q.pollFirst();
			}
			else if(s.equals("deleteLast")) {
					Q.pollLast();
			}	
		}

        boolean first = true;
        for(int i : Q){
            System.out.print((first ? "" : " ") + i);
             
            if(first){
                first = false;
            }
        }
        System.out.println();

		sc.close();
	}

	void debug(Object... o) {
		System.out.println(Arrays.deepToString(o));
	}

	public static void main(String[] args) {
		new Main().run();
	}
}