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;
import java.util.ArrayList;
import java.util.Iterator;
import java.util.ListIterator;
class Main {
   public static void main(String[] args){
		Scanner scan = new Scanner(System.in);
		String[] t = scan.nextLine().split("\\s");
		int n = Integer.parseInt(t[0]);
		ArrayList<Integer> list = new ArrayList<Integer>();

		for(int i = 0; i < n; i++){
			String[] str = scan.nextLine().split("\\s");
			String meirei = str[0];

			if(meirei.equals("insert")){
				list.add(Integer.parseInt(str[1]));
			}else if(meirei.equals("delete")){
				for(int j = list.size() - 1; j >= 0; j--){
					if(Integer.parseInt(str[1]) == list.get(j)){
						list.remove(j);
						break;
					}
				}
			}else if(meirei.equals("deleteFirst")){
				list.remove(list.size() - 1);
			}else if(meirei.equals("deleteLast")){
				list.remove(0);
			}
		}
		
		/*for(int i = list.size() - 1; i >= 0; i--){
			if(i != 0){
				System.out.print(list.get(i) + " ");
			}else{
				System.out.println(list.get(i));
			}
		}*/
		
		
		for(Iterator<Integer> iterator = list.listIterator(list.size()); ((ListIterator<Integer>) iterator).hasPrevious();) {
			Integer lists = ((ListIterator<Integer>) iterator).previous();
			System.out.print(lists + " ");
		}
	}
	
}