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.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.util.ArrayDeque;
import java.util.Deque;



public class Main {

	public static void main(String[] args) throws NumberFormatException, IOException {
		// TODO ?????????????????????????????????????????????

		BufferedReader in = new BufferedReader(new InputStreamReader(System.in));

		int n = Integer.parseInt(in.readLine());
		
		//Scanner sc = new Scanner(System.in);
		//String line1 = sc.nextLine();
		//int n = Integer.parseInt(line1);

		Deque<Integer> list = new ArrayDeque<Integer>();

		for (int i = 0; i < n; i++) {
			String kari = in.readLine();

			// if (kari.equals("deleteFirst")) {
			// list.remove(list.size() - 1);
			// } else if (kari.equals("deleteLast")) {
			// list.remove(0);
			// } else {
			// String[] kari2 = kari.split(" ");
			// int x = Integer.parseInt(kari2[1]);
			// if (kari2[0].equals("insert")) {
			// list.add(x);
			// } else if (kari2[0].equals("delete")) {
			// if (list.contains(x)) {
			// list.remove(list.lastIndexOf(x));
			// }
			// }
			// }

			if (kari.charAt(0) == 'i') {
				list.offerFirst(Integer.parseInt(kari.substring(7)));
			} else if (kari.charAt(6) == 'L') {
				list.removeLast();
			} else if (kari.charAt(6) == 'F') {
				list.removeFirst();
			} else {
				try {
					list.remove(Integer.valueOf(kari.substring(7)));
				} catch (Exception e) {

				}

			}
		}

		// while (list.size() > 1) {
		// System.out.print(list.pop());
		// System.out.print(" ");
		// }
		// System.out.println(list.get(0));

		StringBuilder answer = new StringBuilder();
		while (list.size() > 1) {
			answer.append(list.pop());
			answer.append(" ");
		}
		answer.append(list.pop());
		System.out.println(answer);
	}

}