https://mp.weixin.qq.com/s?__biz=MzI2NjE0MTY0MA==&mid=2652731403&idx=2&sn=2d5648125f380dc5b8e75742b599973a&chksm=f17b72acc60cfbba7accec8c2dcb1b3462373bde7c68dd48ad6f64fe9a346c1e5547641cd33c&scene=27
如果所有的节点的度都比2大的话,那么不管你网络多大、多复杂,里面一定有环路。