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 8u6hxt3HyHkZYnFNVz+fEabgY0+50YEVlfcoocWOWI0Bc17nv7VI9pKjy5Me9ptP