DoublyLinkedListNode* reverse(DoublyLinkedListNode* llist) {
    struct DoublyLinkedListNode* curr = *(&llist);
    struct DoublyLinkedListNode* prev = NULL;
    struct DoublyLinkedListNode* next;

    while (curr != NULL)
    {
        next = curr->next;
        curr->next = prev;
        curr->prev = next;
        prev = curr;
        curr =  next;
    }

    *(&llist) = prev;
    
    return *(&llist);
}