2019 Multi-University,HDU Day 3

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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.