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: Time Limit Exceeded)

import java.util.Scanner;
import java.util.ArrayList;
class Main {
   public static void main(String[] args){
		Scanner scan = new Scanner(System.in);
		int n = scan.nextInt();
		int m = 0;
		String meirei;
		String answer;
		ArrayList<Integer> list = new ArrayList<Integer>();
		
		int i;
		int size;
		
		for(i = 0; i < n; i++){
			 meirei = scan.next();
			 size = list.size();
			 
			if(meirei.equals("deleteFirst")){
					list.remove(size - 1);
			}else if(meirei.equals("deleteLast")){
					list.remove(0);
			}else if(meirei.equals("insert") || meirei.equals("delete")){
				m = scan.nextInt();
				if(meirei.equals("insert")){
					list.add(m);
				}else{
					for(int j = size - 1; j >= 0; j--){
						if(m == list.get(j)){
							list.remove(j);
							break;
						}
					}
				}
			}
		}
		
		size = list.size();
		answer = String.valueOf(list.get(size - 1));
		for(i = size - 2; i >= 0; i--){
			answer += " "; 
			answer += list.get(i);
		}
		
		System.out.println(answer);
	}
	
}