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.LinkedList;
public class Main {

	public static void main(String[] args) {
		Scanner scan=new Scanner(System.in);
		LinkedList<Integer> ll=new LinkedList<Integer>();
		
		String s;
		int x;
		int n=scan.nextInt();
		for(int i=0;i<n;i++){
			s=scan.next();
			if(s.equals("insert")){
				x=scan.nextInt();
				ll.addFirst(x);
			}else if(s.equals("delete")){
				x=scan.nextInt();
				ll.removeFirstOccurrence(x);
			}else if(s.equals("deleteFirst")){
				ll.removeFirst();
			}else{
				ll.removeLast();
			}
		}
		boolean b=false;
		while(!ll.isEmpty()){
			if(!b){
				System.out.print(ll.pollFirst());
				b=true;
			}else{
				System.out.print(" "+ll.pollFirst());
			}
		}
		System.out.println();
		scan.close();
	}

}