2019 Multi-University,HDU Day 3

Problem A

Unsolved.

Problem B

Solved by Xiejiadong && Wwaver_zhu. 01:59:02 (+1)

题意：给出一个 DAG ，每次询问两个点，求有多少方案通过删除一个点，使得其中一个点无法到达所有他所在的联通块出度为 $0$ 的点。

题解：把所有出度为 $0$ 的点连向一个超级汇点，显然，询问就变成了任意一个点无法到达超级汇点的方案。

以超级汇点作为起点，建反图，那么，可以删除的点就一定是从超级汇点出发到询问点的必经点。

在支配树上，方案树就是询问的两个点的祖先的并，求个 lca 就好了。

Problem C

Unsolved.

Problem D

Unsolved.

Problem E

Unsolved.

Problem F

Solved by Kilo_5723 && Weaver_zhu. 00:33:20 (+1)

Problem G

Solved by Xiejiadong. 00:41:23 (+1)

Problem H

Unsolved.

Problem I

Solved by Xiejiadong && Wwaver_zhu. 04:33:20 (+4)

Problem J

Unsolved.

Problem K

Unsolved.