构造一个具有n个外部节点的扩充二叉树，每个外部节点Ki有一个Wi对应，作为该外部节点的权。使得这个扩充二叉树的叶节点带权外部路径长度总和最小： Min( W1 * L1 + W2 * L2 + W3 * L3 + … + Wn * Ln)

Wi:每个节点的权值。

Li:根节点到第i个外部叶子节点的距离。

编程计算最小外部路径长度总和。-Constructing a binary tree with n external expansion nodes, each external node has a Ki Wi corresponds, as the weight of the external node. This extension allows the leaf node of a binary tree with the sum of the minimum length path right outside: Min (W1* L1+ W2* L2+ W3* L3+ ...+ Wn* Ln) Wi: weight for each node. Li: distance　the root node to the i-th external leaf nodes. Programming calculate the sum of the minimum external path length.