A.e=f->data;r=r->next B.e=f->data;r->next=r C.e=f->data;f=f->next D.e=f->data;f->next=f
A.16,12,8,4 B.4,8,12,16 C.8,4,16,12 D.16,12,4,8
A.12 B.5 C.13 D.6