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.io.IOException;
import java.io.PrintWriter;
import java.util.LinkedList;
import java.util.Scanner;

public class Main {

	public static void main(String[] args) throws IOException {

		Scanner sc = new Scanner(System.in);

		int n = sc.nextInt();
		LinkedList<Integer> l = new LinkedList<Integer>();
		for (int i = 0; i < n; i++) {
			String command = sc.next();
			if (command.equals("insert")) {
				Integer operand = Integer.parseInt(sc.next());
				l.add(operand);
			} else if (command.equals("delete")) {
				Integer num = Integer.parseInt(sc.next());
				l.removeLastOccurrence(num);
			} else if (command.equals("deleteFirst")) {
				l.removeLast();
			} else if (command.equals("deleteLast")){
				l.removeFirst();
			} else {
				throw new IllegalArgumentException();
			}
		}

		PrintWriter out = new PrintWriter(System.out);
		for (int i = l.size()-1; i >= 0; i--) {
			out.print(l.get(i));
			if (i != 0) {
				out.print(" ");
			}
		}
		out.print("\n");
		out.flush();
	}

}