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: WA: Presentation Error)

import java.util.Scanner;
class Node{
	Node prev;
	Node next;
	int key;
	Node(){
		prev=this;
		next=this;
		key=-1;
	}
	Node(Node prev,Node next,int key){
		this.prev=prev;
		this.next=next;
		this.key=key;
	}
}
public class Main {
	static Node head,crnt;
	
	static void insert(int key){
		Node tmp=new Node(head,head.next,key);
		head.next=head.next.prev=tmp;
	}
	
	static void remove(){
		if(head.next!=head){
			crnt.prev.next=crnt.next;
			crnt.next.prev=crnt.prev;
			crnt=crnt.prev;
		}
	}
	
	static void delete(int key){
		crnt=head.next;
		while(crnt!=head){
			if(crnt.key==key){
				remove();
				break;
			}
			crnt=crnt.next;
		}
	}
	
	static void deleteFirst(){
		crnt=head.next;
		remove();
	}
	
	static void deleteLast(){
		crnt=head.prev;
		remove();
	}
	
	public static void main(String[] args){
		Scanner scan=new Scanner(System.in);
		int n=scan.nextInt();
		String command;
		int key;
		head=crnt=new Node();
		for(int i=0;i<n;i++){
			command=scan.next();
			if(command.equals("insert")){
				key=scan.nextInt();
				insert(key);
			}else if(command.equals("delete")){
				key=scan.nextInt();
				delete(key);
			}else if(command.equals("deleteFirst")){
				deleteFirst();
			}else{
				deleteLast();
			}
		}
		key=0;
		crnt=head.next;
		while(crnt!=head){
			if(key==0){
				System.out.print(crnt.key);
				key++;
			}else{
				System.out.print(" "+crnt.key);
			}
			crnt=crnt.next;
		}
		scan.close();
	}
}