说明：  　给定一棵树T，树中每个顶点u都有一个权w(u)，权可以是负数。现在要找到树T的一个连通子图使该子图的权之和最大。
(given a tree T, tree each vertex u have a right to w (u), the right to be negative. Now to find a tree T connectivity graph so that the graph of the rights and the largest.)