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;

public class Main {
	
	static DLL nil = new DLL(-1);

	public static void init() {
		nil.setPrev(nil);
		nil.setNext(nil);
	}
	
	public static void insert(int key) {
		DLL node = new DLL(key);
		node.setNext(nil.getNext());
		node.setPrev(nil);
		nil.getNext().setPrev(node);
		nil.setNext(node);
	}
	
	public static DLL listSearch(int key) {
		DLL current = nil.getNext();
		while (!current.equals(nil)) {
			if (current.getValue()==key)
				return current;
			else
				current = current.getNext();				
		}
		return null;
	}
	
	public static void deleteNode(DLL node) {
		if (node == null) return;
		if (nil.equals(node)) return;
		node.getPrev().setNext(node.getNext());
		node.getNext().setPrev(node.getPrev());
		node = null;
	}
	
	public static void deleteFirst() {
		deleteNode(nil.getNext());
	}
	
	public static void deleteLast() {
		deleteNode(nil.getPrev());
	}
	
	public static void deletekey(int key) {
		deleteNode(listSearch(key));
	}
	
	public static void printList() {
		DLL current = nil.getNext();
		while (!current.equals(nil)) {
			if (current.getNext().equals(nil))
				System.out.println(current.getValue());
			else
				System.out.print(current.getValue() + " ");
			current = current.getNext();
		}
	}
	
	public static void main(String[] args) {
		
		init();
		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]))
				insert(Integer.parseInt(tmp[1]));
			else if ("deleteFirst".equals(tmp[0]))
				deleteFirst();
			else if ("deleteLast".equals(tmp[0]))
				deleteLast();
			else
				deletekey(Integer.parseInt(tmp[1]));
		}
		sc.close();
		printList();
	}
	

}

class DLL {
	private int value;
	private DLL prev=null, next=null;
	public int getValue() {
		return value;
	}
	public void setValue(int value) {
		this.value = value;
	}
	public DLL getPrev() {
		return prev;
	}
	public void setPrev(DLL prev) {
		this.prev = prev;
	}
	public DLL getNext() {
		return next;
	}
	public void setNext(DLL next) {
		this.next = next;
	}
	public DLL(int value, DLL prev, DLL next) {
		super();
		this.value = value;
		this.prev = prev;
		this.next = next;
	}
	public DLL() {
		super();
	}
	public DLL(int value) {
		this.value = value;
	}
	
}