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 PHP (judge verdict: Accepted)

<?php

class Simulator
{
    public $array = array();
    public $n_operations;
    public $operations;

    public function __construct()
    {
        fscanf(STDIN, '%d', $this->n_operations);
        $this->operations = new \SplDoublyLinkedList();
        while ($this->n_operations > 0) {
            $word = trim(fgets(STDIN));
            if ($word[0] === 'i') {
                $this->operations->unshift(substr($word, 7));
            } elseif ($word[6] === 'F') {
                $this->operations->shift();
            } elseif ($word[6] === 'L') {
                $this->operations->pop();
            } else {
                foreach ($this->operations as $key => $element) {
                    if ($element === substr($word, 7)) {
                        $this->operations->offsetUnset($key);
                        break;
                    }
                }
            }
            $this->n_operations -= 1;
        }
    }

    public function getAnswer()
    {
        $str = array();
        // var_dump($this->operations);
        while (1) {
            if (count($this->operations) > 0) {
                $array[] = $this->operations->shift();
            } else {
                break;
            }
        }
        echo implode(' ', $array), PHP_EOL;

        // var_dump($array);
        // while (1) {
        //     try {
        //         $element = $this->operations->shift();
        //         $str[] = $element;
        //     } catch (Exception $e) {
        //         echo implode(' ', $str), PHP_EOL;
        //         break;
        //     }
        // }
    }
}

$answer = new Simulator();
$answer->getAnswer();