2019 杭电多校训练第 7 场

rank	solved	A	B	C	D	E	F	G	H	I	J	K
31	6	O	Ø	.	.	.	O	.	O	.	O	O

A

Solved by Henry.

B

UpSolved by XLor.

树哈希，up and down 树形 dp。

F

Solved by Henry.

H

Solved by Henry.

I

Solved by Forsaken.

J

Solved by Forsaken.

每往前走一步的过程独立，考虑前缀和，期望 dp 即可。