双链表的逆序

typedef struct dnode
{
        int data;
        struct dnode *prior;
        struct dnode *next;
}DNode;

DNode *reverseDNode(DNode *head)
{
        DNode *p = head->next;
        DNode *q = p->next;
        DNode *r = q->next;
        if(head == NULL || head->next ==NULL)
                return head;
        p->next = NULL;
        while(r != NULL)
        {
                q->next = p;
                p->prior = q;
                p = q;
                q = r;
                r = r->next;
        }
        q->next = p;
        p->prior = q;
        head->next = q;
        q->prior = head;
        return head;
}