要求有向树Ｔ的k个顶点组成的集合Ｆ，使cost(F)=∑min w(x)*d(x,u)的值达到最小。在一般情况下，有向树是一棵多叉树，为了便于计算，我们把多叉树变转成为与之等价的二叉树，将每个顶点的第一个儿子做为其父顶点的左儿子顶点，同时增加一个０权０边长的附加顶点做为右儿子顶点。然后对于其他儿子项点以相同方式作为新增附加顶点的左儿子顶点，一直继续下去，直至处理完所有顶点。所得到的二叉树与树Ｔ具有相同的最小耗费。(A set F that consists of the k vertices of the tree T is required to minimize the value of the cost (F) = min w (x) *d (x, U). In general, a directed tree is a multi tree, in order to facilitate the calculation, we put the tree change become the equivalent of two binary tree, the first son of each vertex in the left vertex vertex of the son of her father, additional vertex and add a 0 right side for 0 the right son vertex. Then the left son's vertex in the same way is added to the other son points in the same way, and continues until all the vertices are finished. The two forked tree has the same minimum cost as the tree T.)