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题库练习 Jellyfish and OEIS

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A16215 | $Jellyfish and OEIS$

时间限制1s

内存限制256MB

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题目描述

Jellyfish always uses OEIS to solve math problems, but now she finds a problem that cannot be solved by OEIS: Count the number of permutations $p$ of $[1, 2, \dots, n]$ such that for all $(l, r)$ such that $l \leq r \leq m_l$ , the subarray $[p_l, p_{l+1}, \dots, p_r]$ is not a permutation of $[l, l+1, \dots, r]$ . Since the answer may be large, you only need to find the answer modulo $10^9+7$ .

输入格式

The first line of the input contains a single integer $n$ ( $1 \leq n \leq 200$ ) — the length of the permutation. The second line of the input contains $n$ integers $m_1, m_2, \dots, m_n$ ( $0 \leq m_i \leq n$ ).

输出格式

Output the number of different permutations that satisfy the conditions, modulo $10^9+7$ .

输入输出样例

输入 #1

3
1 2 3

输出 #1

输入 #2

5
2 4 3 4 5

输出 #2

输入 #3

5
5 1 1 1 1

输出 #3

C++ 编辑器

输入

输出