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.ArrayList;
import java.util.Scanner;

public class Main {
	public static void main(String[] args) {
		Scanner stdIn = new Scanner(System.in);
		
		int n = stdIn.nextInt();
		ArrayList<Integer> list = new ArrayList<Integer>(n);
		String com = stdIn.nextLine();
		for (int i = 0; i < n; i++) {
			com = stdIn.nextLine();
			if (com.substring(0, 6).equals("insert"))
				insertKey(list, Integer.parseInt(com.substring(7)));
			else {
				if (com.charAt(6) == ' ')
					deleteKey(list, Integer.parseInt(com.substring(7)));
				else if (com.charAt(6) == 'F')
					deleteFirstMember(list);
				else
					deleteLastMember(list);
			}
		}
		
		for (int i = 0; i < list.size(); i++) {
			if (i !=list.size() - 1)
				System.out.print(list.get(i) +" ");
			else 
				System.out.println(list.get(i));
		}
	}
	
	public static void insertKey(ArrayList<Integer> l, int x) {
		l.add(0, x);
	}
	
	public static void deleteKey(ArrayList<Integer> l, int x) {
		int xat = l.indexOf(x);
		l.remove(xat);
	}
	
	public static void deleteFirstMember(ArrayList<Integer> l) {
		l.remove(0);
	}
	
	public static void deleteLastMember(ArrayList<Integer> l) {
		l.remove(l.size() - 1);
	}
}