Refact.ai Match 1 (Codeforces Round 985)
H
Message Spread
Codeforces
3500
原题
← GI →
翻译中…

Given is an undirected graph with $n$ vertices and $m$ edges. Each edge connects two vertices $(u, v)$ and has a probability of $\frac{p}{q}$ of appearing each day.

翻译中…

Initially, vertex $1$ has a message. At the end of the day, a vertex has a message if and only if itself or at least one of the vertices adjacent to it had the message the day before. Note that each day, each edge chooses its appearance independently.

翻译中…

Calculate the expected number of days before all the vertices have the message, modulo $998\,244\,353$.

翻译中…

Input

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The first line contains two integers $n$ and $m$ ($1\leq n\leq 21$, $n-1\leq m\leq\frac{n(n-1)}{2}$).

翻译中…

Then $m$ lines follow, each containing four integers $u$, $v$, $p$, and $q$ ($1\leq u\neq v\leq n$, $1\leq p \lt q \lt 998\,244\,353$, $\gcd(p,q)=1$) — there is an undirected edge between $u$ and $v$, and it has a probability of appearance of $\frac{p}{q}$ each day.

翻译中…

It is guaranteed that there are no self-loops or multiple-edges in the graph and that the graph is connected if all of the edges appear.

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Additional constraint in the input: Let $g_{i,j}$ be the probability of appearance of the edge between $i$ and $j$ ($g_{i,j}=0$ if there is no edge between $i$ and $j$). It is guaranteed that for any $S\subseteq\{1,2,\ldots,n\}$ ($|S|\ge 1$), $$ \prod_{i\in S}\left(\prod_{j\in\{1,2,\ldots,n\}\setminus S}(1-g_{i,j})\right)\not\equiv1\pmod{998\,244\,353}. $$

翻译中…

Output

翻译中…

Print a single integer in the only line of the output — the expected number of days, modulo $998\,244\,353$.

翻译中…

Formally, let $M = 998\,244\,353$. It can be shown that the exact answer can be expressed as an irreducible fraction $\frac{p}{q}$, where $p$ and $q$ are integers and $q \not \equiv 0 \pmod{M}$. Output the integer equal to $p \cdot q^{-1} \bmod M$. In other words, output such an integer $x$ that $0 \le x \lt M$ and $x \cdot q \equiv p \pmod{M}$.

翻译中…

Note

翻译中…

In the first test, the answer is equal to the expected number of days before the only edge in the graph first appears, and that is $\frac{1}{0.1}=10$.

翻译中…

In the second test, the answer is equal to $\frac{20}{9}$ before it is taken modulo $998\,244\,353$.

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In the third test, the only vertex already has the message, so the answer is $0$.

翻译中…

样例

Input #1
2 1
1 2 1 10
Output #1
10
InputCopy OutputCopy
Input #2
3 3
1 2 1 2
1 3 1 2
2 3 1 2
Output #2
887328316
InputCopy OutputCopy
Input #3
1 0
Output #3
0
InputCopy OutputCopy
Input #4
5 8
1 2 1 11
1 3 2 11
1 4 3 11
1 5 4 11
2 4 5 11
2 5 6 11
3 4 7 11
4 5 8 11
Output #4
469993557
InputCopy OutputCopy
Input #5
21 22
1 2 3 4
2 3 4 5
3 4 5 6
5 6 7 8
6 7 8 9
7 8 9 10
8 9 2 3
9 10 3 4
10 11 4 5
11 12 5 6
12 13 6 7
13 14 7 8
14 15 8 9
15 16 9 10
16 17 2 3
17 18 3 4
18 19 4 5
19 20 5 6
20 21 6 7
1 10 100 1001
15 4 147 220
4 11 1 998244352
Output #5
299529765
InputCopy OutputCopy
题目信息
题号
2029H
时间限制
12 s
内存限制
1024 MB
标签
位运算
暴力
组合数学
动态规划

题面与样例版权归 Codeforces 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。