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.util.Scanner;

class List{
	int num;

	public List(int n){
		num=n;
	}

	public void Show(){
		System.out.print(num);
	}
}

public class Main{
	public static void main(String[] args){
		Scanner scan=new Scanner(System.in);
		int i,j,n,num,start=0,end=0,f=0;
		String com="";
		n=scan.nextInt();
		List[] list=new List[n];
		for(i=0;i<n;i++){
			com=scan.next();
			switch(com){
				case "insert":
					num=scan.nextInt();
					for(j=end-1;j>=start;j--){
						list[j+1]=list[j];
					}
					list[start]=new List(num);
					end++;
					break;
				case "delete":
					num=scan.nextInt();
					for(j=start;j<end;j++){
						if(list[j].num==num){
							f=1;
							break;
						}
					}
					if(f==1){
						for(j+=0;j<end-1;j++){
							list[j]=list[j+1];
						}
						list[end]=null;
						end--;
					}
					f=0;
					break;
				case "deleteFirst":
					list[start]=null;
					start++;
					break;
				case "deleteLast":
					list[end]=null;
					end--;
					break;
				default:
					continue;
			}
		}
		for(i=start;i<end;i++){
			list[i].Show();
			if(i<end-1){
				System.out.print(" ");
			}
		}
		System.out.println();
	}
}