/**
     * ~~~ Pointer magic ~~~
     * The address of the next pointer of the previous element
     * In case of index == 0: Address of the head
     * @param index the index
     * @return the address of the next pointer of the previous element
     */
    std::shared_ptr<ListNode<T>> *prevElementNextPointer(unsigned int index) const {
        auto *to_return = const_cast<std::shared_ptr<ListNode<T>> *>(&head);

        if (2 * index <= length + 3) {
            for (unsigned int i = 0; i < index; i++)
                to_return = &((*to_return)->next);
        } else {
            ListNode<T> *curr_pointer = (*to_return).get();
            for (unsigned int i = length + 1; i >= index; i--)
                curr_pointer = (curr_pointer->prev).lock().get();
            to_return = &curr_pointer->next;
        }

        return to_return;
    }