A.f->prior=p;f->next=p->next;p->next=f;p->next->prior=f; B.p->next=f;f->prior=p;p->next->prior=f;f->next=p->next; C.f->prior=p;f->next=p->next;p->next->prior=f;p->next=f; D.p->next=f;p->next->prior=f;f->prior=p;f->next=p->next;
A.8,6,4,2 B.2,4,6,8 C.4,2,8,6 D.8,6,2,4
A."n" B.字符n C."E" D.字符E
A.f=r->next; B.r=r->next; C.r=f->next; D.f=f->next;
A.20 B.15 C.10 D.5