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.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.util.ArrayList;
import java.util.List;

public class Main {

	public static void main(String[] args) throws IOException, NumberFormatException {
		
		BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
		List<String> list = new ArrayList<String>();
		
		int n = Integer.parseInt(br.readLine());
		
		for(int i = 0; i < n; i++){
			String[] str = br.readLine().split(" ");
			
			switch (str[0]){
			case "insert":
				list.add(0, str[1]);
				break;
				
			case "delete":
				if(list.indexOf(str[1]) >= 0){
					list.remove(list.indexOf(str[1]));
				}
				break;
				
			case "deleteFirst":
				list.remove(0);
				break;
				
			case "deleteLast":
				list.remove(list.size() - 1);
				break;
			}
		}
		
		for(int i = 0; i < list.size(); i++){
			System.out.print(list.get(i));
			
			if(i + 1 == list.size()){
				System.out.print("\n");
			} else {
				System.out.print(" ");
			}
		}
	}

}