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.Scanner;

public class Main {
	public static void main (String [] args) {
		Scanner scan = new Scanner (System.in);
		final String NULL = "-";
		final int n = scan.nextInt();
		int count = n + 1, top = n;
		String [] str = new String[n + 1];
		
		for (int i = 0; i < n; i++) {
			final String ord = scan.next();
			final String word;
			switch (ord) {
			case "insert":
				word = scan.next();
				count--;
				str[count] = word;
				break;
			case "delete":
				word = scan.next();
				for (int j = n; j >= count; j--) {
					if (str[j] == word) {
						str[j] = NULL;
						break;
					}
				}
				break;
			case "deleteFirst":
				for (int j = count; j < n; j++) {
					if (str[j].equals(NULL) == false) {
						str[j] = NULL;
						break;
					}	
				}
				break;
			case "deleteLast":
				for ( int j = n; j >= count; j--) {
					if (str[j].equals(NULL) == false) {
						str[j] = NULL;
						break;
					}
				}
			break;
			default:
				break;
			}
		}
		scan.close();
		for (int i = count; i <= n; i++) {
			if (str[i].equals(NULL) == false) {
				top = i;
			}
		}
		for (int i = count; i <= top; i++) {
			if (str[i].equals(NULL) == false) {
				System.out.print(str[i]);
				if (i == top) System.out.println();
				else System.out.print(" ");
			}
			
		}
	}
}