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.*;

class Main{
        static BufferedReader br = new BufferedReader(new InputStreamReader(System.in));

        public static void main(String[] args) throws IOException{
                int num = Integer.parseInt(br.readLine());
                Deque<String> ar = new ArrayDeque<>(num);
                for(int i=0; i<num; i++){
                        int val;
                        String strs = br.readLine();
                        if(strs.charAt(0) == 'i')
                                ar.addFirst(strs.substring(7));
                        else if(strs.charAt(6) == 'F')
                                ar.removeFirst();
                        else if(strs.charAt(6) == 'L')
                                ar.removeLast();
                        else
                                ar.remove(strs.substring(7));
                }
                String j = ar.poll();
                while(j != null){
                        System.out.print(j);
                        j = ar.poll();
                        if(j!=null)
                                System.out.print(" ");
                }
                System.out.println();
        }
}