A.p->next=NULL B.p->next=head C.p=NULL D.p=head
A.2n+2 B.n+1 C.n-1 D.2n-2
A.ph=p;p->next=ph B.p->next=Ph;p=ph C.p->next=ph->next;ph=p D.p->next=ph->next;ph->next=p