AtCoder Grand Contest 022
F
Checkers
AtCoder
⌀ 3606
原题
← E→
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Problem Statement

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Let $X = 10^{100}$. Inaba has $N$ checker pieces on the number line, where the $i$-th checker piece is at coordinate $X^{i}$ for all $1 \leq i \leq N$.

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Every second, Inaba chooses two checker pieces, $A$ and $B$, and move $A$ to the symmetric point of its current position with respect to $B$. After that, $B$ is removed. (It is possible that $A$ and $B$ occupy the same position, and it is also possible for $A$ to occupy the same position as another checker piece after the move).

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After $N - 1$ seconds, only one checker piece will remain. Find the number of distinct possible positions of that checker piece, modulo $10^{9} + 7$.

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Constraints

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  • $1 \leq N \leq 50$
  • $N$ is an integer.
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Input

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Input is given from Standard Input in the following format:

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N

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Output

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Print the number of distinct possible positions of the final checker piece, modulo $10^{9} + 7$.

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样例

Input #1
3
Output #1
12
There are $3$ checker pieces, positioned at $10^{100}, 10^{200}, 10^{300}$ respectively. Call them $A, B, C$ respectively. Here are two (of the $12$) possible sequence of moves : - Let $A$ jump over $B$ in the first second, and let $A$ jump over $C$ in the second second. The final position of $A$ is $2 \times 10^{300} - 2 \times 10^{200} + 10^{100}$. - Let $C$ jump over $A$ in the first second, and let $B$ jump over $C$ in the second second. The final position of $B$ is $-2 \times 10^{300} - 10^{200} + 4 \times 10^{100}$. There are a total of $3 \times 2 \times 2 = 12$ possible sequence of moves, and the final piece are in different positions in all of them.
Input #2
4
Output #2
84
Input #3
22
Output #3
487772376
Remember to output your answer modulo $10^{9} + 7$.
题目信息
题号
agc022_f
时间限制
2 s
内存限制
256 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。