classSolution {public: ListNode*detectCycle(ListNode *head) { ListNode dum(0); dum.next =head; ListNode*sp = &dum; ListNode*fp = &dum;while(sp &&fp) { sp= sp->next; fp= fp->next;if(fp) fp = fp->next;if(sp == fp)break; }if(!fp)returnnullptr; sp= &dum;while(sp !=fp)...