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: Runtime Error)


import java.util.LinkedList;
import java.util.Scanner;

public class Main {

	public static void main(String[] args) {
		LinkedList<Integer> ll = new LinkedList<Integer>();
		Scanner sc = new Scanner(System.in);
		int size = Integer.parseInt(sc.nextLine());
		for (int i=0; i<size; i++) {
			String[] tmp = sc.nextLine().split(" ");
			if ("insert".equals(tmp[0]))
				ll.add(0, Integer.parseInt(tmp[1]));
			else if ("deleteFirst".equals(tmp[0]))
				ll.removeFirst();
			else if ("deleteLast".equals(tmp[0]))
				ll.removeLast();
			else {
				int pos = ll.indexOf(Integer.parseInt(tmp[1]));
				ll.remove(pos);
			}
		}
		int i=0, llsize=ll.size();
		while (i<llsize) {
			if (i==llsize-1) System.out.println(ll.get(i));
			else System.out.print(ll.get(i) + " ");
			i ++;
		}
	}

}