https://ac.nowcoder.com/acm/contest/35/D
对于某个点x,以x为根的子树上，所有与x距离大于等于k的点与x的距离之和。

解法一：离线处理。
https://ac.nowcoder.com/acm/contest/view-submission?submissionId=44771875
解法二：bfs剪枝(竟然能过
https://ac.nowcoder.com/acm/contest/view-submission?submissionId=44771300