AtCoder Grand Contest 071
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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 a length-$N$ integer sequence $f(P)$ as follows.
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- Initialize an integer sequence
$X$with$X=(P_1,P_2,\dots,P_N)$. Repeat the following operation until$X$is a strictly increasing sequence. (It can be shown that$X$will be a strictly increasing sequence in a finite number of operations for any permutation$P$.) Let$C_x$be the number of times an integer$x$is moved to the end during this series of operations. Then, define$f(P)=(C_1,C_2,\dots,C_N)$. - Let
$k$be the smallest index$i$($1 \leq i < N$) such that$X_i > X_{i+1}$. Move the$k$-th element of$X$to the end. More precisely, replace$X$with$(X_1,X_2,\dots,X_{k-1},X_{k+1},X_{k+2},\dots,X_N,X_{k})$.
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Find the number, modulo a prime number $M$, of distinct sequences that can occur as $f(P)$.
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Constraints
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$1 \leq N \leq 500$$10^8 \leq M \leq 10^9$$M$is prime.- 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 M
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Output
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Print the answer.
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样例
Input #1
4 998244353
Output #1
8
For example, when $P=(1,4,3,2)$, we initialize $X=(1,4,3,2)$ and perform operations as follows:
1. Since $X_1 \leq X_2$ but $X_2 > X_3$, the element $X_2=4$ is moved to the end, and $X$ becomes $(1,3,2,4)$.
2. $X_2=3$ is moved to the end, and $X$ becomes $(1,2,4,3)$.
3. $X_3=4$ is moved to the end, and $X$ becomes $(1,2,3,4)$.
The number of times $1,2,3,4$ are moved to the end is $0,0,1,2$, respectively, so $f(P)=(0,0,1,2)$.
Input #2
71 998244353
Output #2
473972314
Input #3
300 923223991
Output #3
333532467
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。