AtCoder Grand Contest 054
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Problem Statement
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Given are integers $N$ and $A$. Find the number, modulo $998244353$, of permutations $P=(P_1,P_2,\cdots,P_N)$ of $(1,2,\cdots,N)$ that satisfy the following conditions.
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$P_1=A$.- It is possible to repeat the following operation so that
$P$has just two elements. - Choose three consecutive elements
$x$,$y$, and$z$. Here,$y<\min(x,z)$or$y>\max(x,z)$must hold. Then, erase$y$from$P$.
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Solve $T$ test cases in an input file.
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Constraints
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$1 \leq T \leq 5 \times 10^5$$3 \leq N \leq 10^6$$1 \leq A \leq N$- All values in input are integers.
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Input
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Input is given from Standard Input in the following format:
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T
case_1
case_2
\vdots
case_T
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Each case is in the following format:
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N A
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Output
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Print the answer for each test case.
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样例
Input #1
8
3 1
3 2
3 3
4 1
4 2
4 3
4 4
200000 10000
Output #1
1
2
1
3
5
5
3
621235018
When $N=4,A=2$, one permutation that satisfies the condition is $P=(2,1,4,3)$. One way to make it have just two elements is as follows.
- Choose $(x,y,z)=(2,1,4)$ to erase $1$, resulting in $P=(2,4,3)$.
- Choose $(x,y,z)=(2,4,3)$ to erase $4$, resulting in $P=(2,3)$.
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。