prim算法输出一个最小生成树，prim算法最先是找到一个根节点，然后在继续生成最小生成树，这样就能找到一个最小生成树，如果是这样的话，我们可以用一个循环，把每一个节点当作根节点，再把重复的树删除，这样就能找到所有的最小生成树了-algorithm prim, prim algorithm was first to find a root node, and then continue to generate the minimum spanning tree, so that we can find a minimum spanning tree, if that is the case, we can use a loop to each node when as root, then repeat the tree removed, so you can find all of the minimum spanning tree