typedef struct node
    {
      ElemType data;
      struct node *prior
      struct node *next;
    }list;

 list *reverselist(list *head)
    {
      if ((NULL == head) || (NULL == head->next))
      {
        return head;
      }
      list *p1=head->next, *p2=p1->next, *p3=NULL;
      p1->next = NULL;
      while (p2)
      {
        p3 = p2->next;      // 保存当前结点的下一结点
        p2->next = p1;      // 改变当前结点的next域，指向它的前一个结点
        p1->prior = p2;     // 改变前一个结点的prior域，指向它的后一个结点
        p1 = p2;         // 指针移到下一个结点
        p2 = p3;
      }
      head->next = p1;       // 恢复头结点
      p1->prior = head;
      return head;
    }

 list *reverselist(list *head)
    {
      if ((NULL == head) || (NULL == head->next))
      {
        return head;
      }
      list *p1=head, *p2=p1->next, *p3=NULL;
      p1->next = NULL;
      while (p2)
      {
        p3 = p2->next;
        p2->next = p1;
        p1->prior = p2;
        p1 = p2;
        p2 = p3;
      }
      head = p1;
      return head;
    }