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: Accepted)

import java.util.*;
import java.io.*;

public class Main {
	public static void main(String[] args) throws NumberFormatException,IOException {
		
		BufferedReader input = new BufferedReader(new InputStreamReader(System.in));
		StringBuilder output = new StringBuilder();
		
		int n = Integer.parseInt(input.readLine());
		
		Deque<Integer> List = new ArrayDeque<Integer>();
		
		for (int i = 0; i < n; i++) {
			
			String order = input.readLine();
			
			if(order.charAt(0) == 'i') { List.push(Integer.parseInt(order.substring(7))); }
			else if(order.charAt(6)=='F') { List.removeFirst(); }
			else if(order.charAt(6)=='L') { List.removeLast(); }
			else { List.remove(Integer.parseInt(order.substring(7))); }
		}
		
		output.append(List.poll());
		for(int num2 : List) { output.append(" ").append(num2); }
		System.out.println(output);
	}
}