AtCoder Grand Contest 058
B
Adjacent Chmax
AtCoder
⌀ 2053
原题
← AC →
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Problem Statement

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You are given a permutation $P=(P_1,P_2,\cdots,P_N)$ of $(1,2,\cdots,N)$.

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You may perform the following operation zero or more times.

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  • Choose an integer $i$ ($1 \leq i \leq N-1$). Let $v=\max(P_i,P_{i+1})$ and replace the values of $P_i$ and $P_{i+1}$ with $v$.
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How many sequences are there that $P$ can be after your operations? Find the count modulo $998244353$.

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Constraints

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  • $2 \leq N \leq 5000$
  • $(P_1,P_2,\cdots,P_N)$ is a permutation of $(1,2,\cdots,N)$.
  • 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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N
P_1 P_2 \cdots P_N

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Output

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Print the answer.

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样例

Input #1
3
1 3 2
Output #1
4
The four sequences that $P$ can become are $(1,3,2)$, $(3,3,2)$, $(1,3,3)$, and $(3,3,3)$.
Input #2
4
2 1 3 4
Output #2
11
Input #3
10
4 9 6 3 8 10 1 2 7 5
Output #3
855
题目信息
题号
agc058_b
时间限制
2 s
内存限制
1024 MB

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。