给定一个带有根R的非空树，并赋给每个树节点TI的权重WI。从R到L的路径的重量被定义为从R到任何叶节点L的路径上所有节点的权重之和。(Given a non-empty tree with root R, and with weight Wi assigned to each tree node Ti. The weight of a path from R to L is defined to be the sum of the weights of all the nodes along t