AtCoder Grand Contest 058
翻译中…
Problem Statement
翻译中…
For an undirected tree $t$, let us define a rational number $f(t)$ as follows.
翻译中…
- Let
$n$be the number of vertices in$t$. - If
$n=1$: Let$f(t)=1$. - If
$n \geq 2$: - For an edge
$e$in$t$, we denote by$t_x(e)$and$t_y(e)$the two trees that result from deleting$e$from$t$(in arbitrary order).- Let
$f(t)=(\sum_{e \in t} f(t_x(e)) \times f(t_y(e)))/n$.
- Let
翻译中…
You are given a tree $T$ with $N$ vertices numbered $1$ to $N$. The $i$-th edge connects Vertex $A_i$ and Vertex $B_i$.
翻译中…
Find the value $f(T)$ $\text{mod }{998244353}$.
翻译中…
What is a rational number $\text{mod }{998244353}$? Under the Constraints of this problem, when the sought rational number is represented as $\frac{P}{Q}$, it can be proved that $Q \neq 0 \pmod{998244353}$. Therefore, there is a unique integer $R$ such that $R \times Q \equiv P \pmod{998244353}, 0 \leq R < 998244353$. Find this $R$.
翻译中…
Constraints
翻译中…
$2 \leq N \leq 5000$$1 \leq A_i,B_i \leq N$- The given graph is a tree.
翻译中…
Input
翻译中…
Input is given from Standard Input in the following format:
翻译中…
N
A_1 B_1
A_2 B_2
\vdots
A_{N-1} B_{N-1}
翻译中…
Output
翻译中…
Print the answer.
翻译中…
样例
Input #1
2
1 2
Output #1
499122177
We have $f(T)=1/2$.
Input #2
3
1 2
2 3
Output #2
332748118
We have $f(T)=1/3$.
Input #3
4
1 2
2 3
3 4
Output #3
103983787
Input #4
10
4 5
1 9
6 1
8 4
5 9
4 7
3 10
5 2
4 3
Output #4
462781191
题目信息
题面与样例版权归 AtCoder 及出题人所有;中文翻译由 AI 生成(CI 管线),如有出入请以原文为准。