说明：  kthtree问题 给定一棵有向树T，树T 中每个顶点u都有一个权w(u)；树的每条边(u,v)也都有一个 非负边长d(u,v)。有向树T的每个顶点u 可以看作客户，其服务需求量为w(u)。每条边(u,v)的边长d(u,v) 可以看作运输费用。如果在顶点u 处未设置服务机构，则将顶点u 处的服务需求沿有向树的边(u,v)转移到顶点v 处服务机构需付出的服务转移费用为w(u)*d(u,v)。 树根处已设置了服务机构，现在要在树T中增设k处服务机构，使得整棵树T 的服务转移费用最小
(kthtree problems to be fixed to a tree T, T trees each vertex u have a right to w (u); Tree edges (u, v) also have a non-negative side length d (u, v). T to a tree each vertex u can be seen as customers, the demand for its services w (u). Edges (u, v) of length d (u, v) can be considered as transportation costs. If the vertex u Department had not set up the service agencies, will be the culmination u demand for services to a tree along the edge (u, v) v transferred to Vertex's services agencies are required to pay a service fee for the transfer of w (u)* d (u, v). Christopher has set up a service sector, is now in the tree to add k T's services agencies, T entire tree makes the shift to the smallest cost)