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.*;

public class Main {
	public static void main(String[] args) {
		ALDS1_3_C();
	}

	public static void ALDS1_3_C() {

		Scanner sc = new Scanner(System.in);
		BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
		Deque<String> link = new ArrayDeque<String>();
		String input_str[] = new String[2];
		try {
			int n = Integer.parseInt(br.readLine());
			for(int i = 0; i < n; i++) {
				//String command = sc.next();
				input_str = br.readLine().split("\\s+");
				if(input_str[0].equals("insert")) {
					link.addFirst(input_str[1]);
				}else if(input_str[0].equals("delete")) {
					link.remove(input_str[1]);
				}else if(input_str[0].equals("deleteFirst")) {
					link.removeFirst();
				}else if(input_str[0].equals("deleteLast")) {
					link.removeLast();
				}

			}

			String tmp;
			boolean notFirst = false;
			while((tmp = link.poll()) != null) {
				if(notFirst)
					System.out.print(" ");
				System.out.print(tmp);
				notFirst = true;
			}
			System.out.println();
		} catch (IOException e) {
			e.printStackTrace();
		}
	}

}