View source for 2020-2021 ACM-ICPC, Asia Seoul Regional Contest


== Problem A ==

Upsolved by Kilo_5723. (-4)

== Problem B ==

Solved by Xiejiadong.  00:05 (+)

温暖的签到。

== Problem C ==

Solved by Xiejiadong. 00:35 (+)

题意：给出树上的一点标记点，求所有位于任意两个标记点之间的点个数。

题解：如果一个节点本身自己是标记点，或者至少有两个孩子有标记点，或者一个孩子有标记点且子树中不包含所有的标记点的时候这个节点是位于任意两个之间的。一遍 dfs 就完事了。

== Problem D ==

Unsolved.

== Problem E ==

Solved by Kilo_5723. 00:35 (+)

== Problem F ==

Unsolved.

== Problem G ==

Solved by Kilo_5723. 01:05 (+2)

== Problem H ==

Solved by Xiejiadong. 01:30 (+)

题意：三条平行等间距直线上有一些 hole，求有多少直线可以分别穿过直线上的一个 hole。

题解：其实就是求三条直线上有多少 hole 的位置构成等差数列，即第一条直线+第三条直线=2*第二条直线。直接坐标变换以后 FFT 再合并就可以了。

== Problem I ==

Solved by Weaver_zhu. 01:55 (+)

== Problem J ==

Solved by Kilo_5723. 00:22 (+1)

== Problem K ==

Unsolved.

== Problem L ==

Solved by Kilo_5723. 04:05 (+7)