双向链表翻转

Node* reveser(Node *head)
{
    if (head == NULL)
    {
        return NULL;
    }

    Node* pre = NULL;
    Node* next = NULL;
    while (head != NULL)
    {
        next = head->next;
        head->next = pre;
        head->pre = next;
        pre = head;
        head = next;
    }

    pre->pre = NULL;
    return pre;
}