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.InputStreamReader;
import java.util.Iterator;
import java.util.LinkedList;

public class Main {
	public static void main(String[] args) {

		// LinkedList型としてインスタンス化
		LinkedList<Integer> list = new LinkedList<>();

		try (BufferedReader br = new BufferedReader(new InputStreamReader(System.in));) {
			int n = Integer.parseInt(br.readLine());
			for (int i = 0; i < n; i++) {
				String[] cmd = br.readLine().split(" ");
				switch (cmd[0]) {
				case "insert":
					// リストの先頭に追加
					list.addFirst(Integer.parseInt(cmd[1]));
					break;

				case "delete":
					// parseIntの戻り値はint型である為、
					// そのまま渡すとremove(int index)が呼び出されてしまう。
					// 明示的にInteger型に変換することで、
					// remove(Object o)メソッドを呼び出す。
					list.remove((Integer) Integer.parseInt(cmd[1]));
					break;

				case "deleteFirst":
					// 先頭の要素を削除
					list.removeFirst();
					break;

				case "deleteLast":
					// 末尾の要素を削除
					list.removeLast();
					break;
				}
			}

			StringBuilder sb = new StringBuilder();
			for (Iterator<Integer> it = list.listIterator(); it.hasNext();) {
				sb.append(it.next());
				if (it.hasNext()) {
					sb.append(" ");
				}
			}
			System.out.println(sb);

		} catch (Exception e) {
			e.printStackTrace();
		}

	}

}