there problem cactus NERC 2020 online round that s bad mistake judge decide fix you shall pass World Finals 2021 solve problem cactusA cactus connect undirected graph edge lie simple cycle intuitively cactus generalization tree cycle allow multiedge multiple edge pair vertex loop edge connect vertex allow cactus Cher get cactus she call cactus strong impossible add edge way remain cactus but Cher think cactus strong she wants add small possible number edge strong ieto create new cactus vertex original cactus subgraph new impossible add edge graph remain cactus Cher hire job so