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.io.*;
import java.util.*;

public class Main {
    public static void main(String args[]) {
        int n;
        LinkedList<String> list = new LinkedList<String>();
        Scanner sc = new Scanner(System.in);

        n = sc.nextInt();
        sc.nextLine();

        for (int i = 0; i < n; i++) {
            String s[] = sc.nextLine().split(" ");

            switch (s[0]) {
                case "insert":
                    list.addFirst(s[1]);
                    break;
                case "delete":
                    int idx = list.indexOf(s[1]);
                    if (idx >= 0) list.remove(idx);
                    break;
                case "deleteFirst":
                    list.remove(0);
                    break;
                case "deleteLast":
                    list.remove(list.size() - 1);
                    break;
            }
        }

        for (int i = 0; i < list.size() - 1; i++) {
            System.out.print(list.get(i) + " ");
        }
        System.out.println(list.get(list.size() - 1));

    }
}