Codeforces Round 663 (Div. 2)
C
Cyclic Permutations
Codeforces
1500
原题
← BD →
翻译中…

A permutation of length $n$ is an array consisting of $n$ distinct integers from $1$ to $n$ in arbitrary order. For example, $[2,3,1,5,4]$ is a permutation, but $[1,2,2]$ is not a permutation ($2$ appears twice in the array) and $[1,3,4]$ is also not a permutation ($n=3$ but there is $4$ in the array).

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Consider a permutation $p$ of length $n$, we build a graph of size $n$ using it as follows:

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  • For every $1 \leq i \leq n$, find the largest $j$ such that $1 \leq j \lt i$ and $p_j \gt p_i$, and add an undirected edge between node $i$ and node $j$
  • For every $1 \leq i \leq n$, find the smallest $j$ such that $i \lt j \leq n$ and $p_j \gt p_i$, and add an undirected edge between node $i$ and node $j$
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In cases where no such $j$ exists, we make no edges. Also, note that we make edges between the corresponding indices, not the values at those indices.

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For clarity, consider as an example $n = 4$, and $p = [3,1,4,2]$; here, the edges of the graph are $(1,3),(2,1),(2,3),(4,3)$.

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A permutation $p$ is cyclic if the graph built using $p$ has at least one simple cycle.

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Given $n$, find the number of cyclic permutations of length $n$. Since the number may be very large, output it modulo $10^9+7$.

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Please refer to the Notes section for the formal definition of a simple cycle

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Input

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The first and only line contains a single integer $n$ ($3 \le n \le 10^6$).

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Output

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Output a single integer $0 \leq x \lt 10^9+7$, the number of cyclic permutations of length $n$ modulo $10^9+7$.

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Note

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There are $16$ cyclic permutations for $n = 4$. $[4,2,1,3]$ is one such permutation, having a cycle of length four: $4 \rightarrow 3 \rightarrow 2 \rightarrow 1 \rightarrow 4$.

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Nodes $v_1$, $v_2$, $\ldots$, $v_k$ form a simple cycle if the following conditions hold:

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  • $k \geq 3$.
  • $v_i \neq v_j$ for any pair of indices $i$ and $j$. ($1 \leq i \lt j \leq k$)
  • $v_i$ and $v_{i+1}$ share an edge for all $i$ ($1 \leq i \lt k$), and $v_1$ and $v_k$ share an edge.
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样例

Input #1
4
Output #1
16
InputCopy OutputCopy
Input #2
583291
Output #2
135712853
InputCopy OutputCopy
题目信息
题号
1391C
时间限制
1 s
内存限制
256 MB
标签
组合数学
动态规划
图论
数学

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