Codeforces Round 692 (Div. 1, based on Technocup 2021 Elimination Round 3)
E
No Game No Life
Codeforces
未评级
原题
← DF →
翻译中…

Let's consider the following game of Alice and Bob on a directed acyclic graph. Each vertex may contain an arbitrary number of chips. Alice and Bob make turns alternating. Alice goes first. In one turn player can move exactly one chip along any edge outgoing from the vertex that contains this chip to the end of this edge. The one who cannot make a turn loses. Both players play optimally.

翻译中…

Consider the following process that takes place every second on a given graph with $n$ vertices:

翻译中…
  1. An integer $v$ is chosen equiprobably from $[1, n + 1]$.
  2. If $v \leq n$, we add a chip to the $v$-th vertex and go back to step 1.
  3. If $v = n + 1$, Alice and Bob play the game with the current arrangement of chips and the winner is determined. After that, the process is terminated.
翻译中…

Find the probability that Alice will win the game. It can be shown that the answer can be represented as $\frac{P}{Q}$, where $P$ and $Q$ are coprime integers and $Q \not\equiv 0 \pmod{998\,244\,353}$. Print the value of $P \cdot Q^{-1} \bmod 998\,244\,353$.

翻译中…

Input

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The first line contains two integers $n$ and $m$ — the number of vertices and edges of the graph ($1 \leq n \leq 10^5$, $0 \leq m \leq 10^5$).

翻译中…

The following $m$ lines contain edges description. The $i$-th of them contains two integers $u_i$ and $v_i$ — the beginning and the end vertices of the $i$-th edge ($1 \leq u_i, v_i \leq n$). It's guaranteed that the graph is acyclic.

翻译中…

Output

翻译中…

Output a single integer — the probability of Alice victory modulo $998\,244\,353$.

翻译中…

样例

Input #1
1 0
Output #1
0
InputCopy OutputCopy
Input #2
2 1
1 2
Output #2
332748118
InputCopy OutputCopy
Input #3
5 5
1 4
5 2
4 3
1 5
5 4
Output #3
931694730
InputCopy OutputCopy
题目信息
题号
1464E
时间限制
2 s
内存限制
256 MB

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。