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: Wrong Answer)

import java.io.BufferedOutputStream;
import java.io.PrintStream;
import java.util.*;
public class Main {

	public static void main(String[] args) {
		System.setOut(new PrintStream(new BufferedOutputStream(System.out)));
		Scanner cin=new Scanner(System.in);
		int n=cin.nextInt();
		DLinkedList list=new DLinkedList();
		for(int i=0;i<n;i++) {
			String str=cin.next();
			if(str.equals("insert")) {
				int x=Integer.parseInt(cin.next());
				list.insert(x);
			}
			else if(str.equals("delete")) {
				int x=Integer.parseInt(cin.next());
				list.deleteFact(x);
			}
			else if(str.equals("deleteFirst"))list.deleteFirst();
			else if(str.equals("deleteLast"))list.deleteLast();
			//System.out.println(i);
		}
		
		int lim=list.size();
		for(int i=0;i<lim;i++) {
			if(i==lim-1)System.out.println(list.deleteFirst());
			else System.out.print(list.deleteFirst()+" ");
		}
	}

}

class Cell{
	int data=-1;
	Cell next;
	Cell prev;
	
	Cell(int x){
		data=x;
	}
	
	void setNext(Cell next) {
		this.next=next;
	}
	
	Cell getNext() {
		return next;
	}
	
	void setPrev(Cell prev) {
		this.prev=prev;
	}
	
	Cell getPrev() {
		return prev;
	}
	
	int getData() {
		return data;
	}
}

class DLinkedList{
	Cell dummy;
	int size;
	
	DLinkedList(){
		dummy=new Cell(-1);
		dummy.setNext(dummy);
		dummy.setPrev(dummy);
		size=0;
	}
	
	void insert(int data) {
		Cell c=new Cell(data);
		c.setNext(dummy.getNext());
		c.setPrev(dummy);
		dummy.getNext().setPrev(c);
		dummy.setNext(c);
		size++;
	}
	
	int deleteFirst() {
		Cell c=dummy.getNext();
		if(c==dummy)return -1;
		c.getNext().setPrev(c.prev);
		c.getPrev().setNext(c.getNext());
		size--;
		return c.getData();
	}
	
	int deleteLast() {
		Cell c=dummy.getPrev();
		if(c==dummy)return -1;
		c.getNext().setPrev(c.getPrev());
		c.getPrev().setNext(c.getNext());
		size--;
		return c.getData();
	}
	
	boolean deleteFact(int x) {
		Cell c=dummy.getNext();
		for(int i=0;i<size;i++) {
			if(c.getData()==x) {
				c.getNext().setPrev(c.getPrev());
				c.getPrev().setNext(c.getNext());
				size--;
				return true;
			}
			c=c.getNext();
		}
		return false;
	}
	
	int size() {
		return size;
	}
}