typedef struct DNode{
    int data;
    struct DNode *prior,*next;//前驱指针，后继指针
}DNode,&DList;

//插入操作
① s->next = p->next;
② p->next->prior;
③ s->prior = p;
④ p->next =s;

//删除操作
① p->next = q->next;
② q->next->prior = p;
③ free(q);