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2020-2021:teams:intrepidsword:2020-nowcoder-multi-7

目录

Contest Info

date: 2020-08-01 12:00~17:00

2020牛客暑期多校训练营(第七场)

Solutions

D. Fake News

签到题,只有 $1,24$ 满足要求。

I. Valuable Forests

题目大意:定义一个森林的价值为所有点的度数平方和。求所有 $n$ 个点带标号的森林的价值和。

题解:首先求树的价值平方和。注意到一个点的度数等于 prufer 序列中出现次数加 $1$,且每个点的贡献相同,因而是 $n\cdot\sum_{i=0}^{n-2}(i+1)^{2}{n-2\choose i}$。森林 dp 一下即可。

J. Pointer Analysis

签到题,xjb 迭代即可。