ユニークビジョンプログラミングコンテスト2024 クリスマス(AtCoder Beginner Contest 385)
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Problem Statement
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For a permutation $P=(P_1,P_2,\dots,P_N)$ of $(1,2,\dots,N)$, define integers $L(P)$ and $R(P)$ as follows:
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- Consider
$N$buildings arranged in a row from left to right, with the height of the$i$-th building from the left being$P_i$. Then$L(P)$is the number of buildings visible when viewed from the left, and$R(P)$is the number of buildings visible when viewed from the right. More formally,$L(P)$is the count of indices$i$such that$P_j < P_i$for all$j < i$, and$R(P)$is the count of indices$i$such that$P_i > P_j$for all$j > i$.
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You are given integers $N$ and $K$. Find, modulo $998244353$, the count of all permutations $P$ of $(1,2,\dots,N)$ such that $L(P)-R(P)=K$.
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Constraints
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$1 \leq N \leq 2 \times 10^5$$|K| \leq N-1$- All input values are integers.
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Input
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The input is given from Standard Input in the following format:
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N K
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Output
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Print the answer.
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样例
Input #1
3 -1
Output #1
1
- $P=(1,2,3)$: $L(P)-R(P)=3-1=2$.
- $P=(1,3,2)$: $L(P)-R(P)=2-2=0$.
- $P=(2,1,3)$: $L(P)-R(P)=2-1=1$.
- $P=(2,3,1)$: $L(P)-R(P)=2-2=0$.
- $P=(3,1,2)$: $L(P)-R(P)=1-2=-1$.
- $P=(3,2,1)$: $L(P)-R(P)=1-3=-2$.
Therefore, the number of permutations $P$ with $L(P)-R(P)=-1$ is $1$.
Input #2
1 0
Output #2
1
Input #3
2024 385
Output #3
576300012
Print the count 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。