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.ArrayList;
import java.util.Scanner;

public class Main {
    public static ArrayList<Integer> list = new ArrayList<Integer>();

    public static void main(String[] args) {
        int total;

        Scanner inp = new Scanner(System.in);
        total = inp.nextInt();

        for (int k = 0; k < total; k++) {
            String command = inp.next();

            switch (command) {
                case "insert": {
                    int num = inp.nextInt();

                    insert_x(num);
                    break;
                }
                case "delete": {
                    int num = inp.nextInt();

                    delete_x(num);
                    break;
                }
                case "deleteFirst":
                    deleteFirst();
                    break;
                case "deleteLast":
                    deleteLast();
                    break;
            }
        }

        for (int l = 0; l < list.size(); l++) {
            if (l == 0) {
                System.out.printf("%d", list.get(l));
            } else {
                System.out.printf(" %d", list.get(l));
            }

        }
    }

    public static void insert_x(int num) {
        list.add(0, num);
    }

    public static void delete_x(int num) {
        list.remove(list.indexOf(num));
    }

    public static void deleteFirst() {
        list.remove(0);
    }

    public static void deleteLast() {
        list.remove(list.size()-1);
    }
}