AtCoder Regular Contest 134
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Problem Statement
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There are $N$ coins numbered $1, 2, \ldots, N$ arranged in a row. Initially, all coins face up.
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Snuke chooses a permutation $p$ of $(1,\ldots,N)$ with equal probability, and do $N$ operations. The $i$-th operation does the following.
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- If the coin numbered
$i$faces down, do nothing. - If the coin numbered
$i$faces up, turn that coin over and then turn over the coin numbered$p_i$.
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After the $N$ operations, Snuke will receive $W^k$ yen (Japanese currency) from his mother, where $k$ is the number of coins facing up.
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Find the expected value of the amount Snuke will get, multiplied by $N!$ (it can be proved that this is an integer), modulo $998244353$.
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Constraints
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- All values in input are integers.
$1 \leq N \leq 2 \times 10^5$$1 \leq W < 998244353$
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Input
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Input is given from Standard Input in the following format:
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N W
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Output
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Print the expected value of the amount Snuke will get, multiplied by $N!$, modulo $998244353$.
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样例
Input #1
4 2
Output #1
90
- When $p=(1,4,2,3)$, the operations go as follows.
- In the $1$-st operation, the coin numbered $1$ faces down, and then the coin numbered $1$ faces up.
- In the $2$-nd operation, the coin numbered $2$ faces down, and then the coin numbered $4$ faces down.
- In the $3$-rd operation, the coin numbered $3$ faces down, and then the coin numbered $2$ faces up.
- In the $4$-th operation, nothing is done.
- In the end, two coins face up, so he receives $4$ yen.
Input #2
2 100
Output #2
10001
Input #3
200000 12345
Output #3
541410753
- Be sure to find the value modulo $998244353$.
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。