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.*;
import java.util.*;
 
class Main {
    static BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
    static StringBuilder out = new StringBuilder();
    static ArrayDeque<Integer> li = new ArrayDeque<Integer>();
 
    public static void main(String[] Args) throws IOException {
        int n = Integer.parseInt(br.readLine());
        String in;
        int key;
        for(int i=0; i<n; i++) {
            in = br.readLine();
            if(in.charAt(0) == 'i') {
                key = Integer.parseInt(in.substring(7));
                li.addFirst(key);
            } else if(in.charAt(6) == 'F') {
                li.removeFirst();
            } else if(in.charAt(6) == 'L') {
                li.removeLast();
            } else {
                key = Integer.parseInt(in.substring(7));
                li.remove((Integer) key);
            }
        }
        out.append(li.poll());
        for(int num : li) {
            out.append(' ').append(num);
        }
        out.append('\n');
        System.out.print(out);
    }
 
}