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.util.*;

class Node {
    public int key;
    public Node next, pre;
    Node(int key) {
        this.key = key;
        next = pre = null;
    }
}

public class Main {
    public static void main(String[] args) {
        Scanner scan = new Scanner(System.in);
        int N = scan.nextInt();
        Node head = new Node(0);
        Node last = new Node(0);
        head.next = last;
        last.pre = head;
        while(N-- > 0) {
            String ope = scan.next();
            if(ope.equals("insert")) {
                int num = scan.nextInt();
                Node node = new Node(num);
                node.pre = head;
                node.next = head.next;
                node.pre.next = node;
                node.next.pre = node;
            } else if(ope.equals("delete")) {
                int num = scan.nextInt();
                for(Node p = head.next; p != last; p = p.next) {
                    if(p.key == num) {
                        p.pre.next = p.next;
                        p.next.pre = p.pre;
                    }
                }
            } else if(ope.equals("deleteFirst")) {
                head.next.next.pre = head;
                head.next = head.next.next;
            } else if(ope.equals("deleteLast")) {
                last.pre.pre.next = last;
                last.pre = last.pre.pre;
            }
        }
        for(Node p = head.next; p != last; p = p.next) {
            if(p != head.next) System.out.print(" ");
            System.out.print(p.key);
        }
        System.out.println();
    }
}