说明：  电网规划中搜索环路的程序,通过给定的网络拓扑结构,判定该网络是否连通,如果连通,判定是否有回路,如果有回路,返回组成改回路的线路集合.
(Search network planning process loop through a given network topology, determine whether the connectivity of the network, if connected, to determine whether there is any loop, if loop to loop back to the composition of a collection of lines.)