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.io.PrintWriter;
import java.util.ArrayDeque;

public class Main {
	public static void main(String[] args) throws IOException{
		BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
		PrintWriter pw = new PrintWriter(System.out);
		
		int n = Integer.parseInt(br.readLine());
		ArrayDeque<Integer> list = new ArrayDeque<Integer>();
		for (int i = 0; i < n; i++) {
			String com = br.readLine();
			if (com.charAt(0) == 'i')
				insertKey(list, Integer.parseInt(com.substring(7)));
			else {
				if (com.charAt(6) == ' ')
					deleteKey(list, Integer.parseInt(com.substring(7)));
				else if (com.charAt(6) == 'F')
					deleteFirstMember(list);
				else
					deleteLastMember(list);
			}
		}
		
		pw.print(list.poll());
		for (Integer element : list)
			pw.print(" "+element);
		pw.println();
		pw.close();
	}
	
	public static void insertKey(ArrayDeque<Integer> l, int x) {
		l.addFirst(x);
	}
	
	public static void deleteKey(ArrayDeque<Integer> l, int x) {
		l.removeFirstOccurrence(x);
	}
	
	public static void deleteFirstMember(ArrayDeque<Integer> l) {
		l.removeFirst();
	}
	
	public static void deleteLastMember(ArrayDeque<Integer> l) {
		l.removeLast();
	}
}