如图1-18所示,水里有条鱼,它正在向下游游。请你移动最少的火柴,使它向上游游,那么需要移动几根火柴呢?
图1-18 srJ0zkO9c44RLa/AywWmQaURrh88TsJMMTqYsq9aR23jMuWeU1L3iKpuRPVBtaXz