已知P结点是某双向的中间结点,试从下列提供的语句中选出合适的语句序列,完成下面的操作。 1、 在P结点后插入S结点: 2、 在P结点前插入S结点: 3、删除P结点的直接后继结点: 4、删除P结点的直接前驱结点: 5、删除P结点: (1)P->next = P->next->next; (2)P->prior = P->prior->prior; (3)P->next = S; (4)P->prior = S; (5)S->next = P; (6)S->prior = P; (7)S->next = P->next; (8)S->prior = P->prior; (9)P->prior->next = P->next; (10)P->prior->next = P; (11)P->next->prior = P; (12)P->next->prior = S; (13)P->prior->next = S; (14)P->next->prior = P->prior; (15)Q = P->next; (16)Q = P->prior; (17) free(P); (18)free(Q);