AtCoder Beginner Contest 129
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Problem Statement
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There is a staircase with $N$ steps. Takahashi is now standing at the foot of the stairs, that is, on the $0$-th step. He can climb up one or two steps at a time.
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However, the treads of the $a_1$-th, $a_2$-th, $a_3$-th, $\ldots$, $a_M$-th steps are broken, so it is dangerous to set foot on those steps.
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How many are there to climb up to the top step, that is, the $N$-th step, without setting foot on the broken steps? Find the count modulo $1\ 000\ 000\ 007$.
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Constraints
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$1 \leq N \leq 10^5$$0 \leq M \leq N-1$$1 \leq a_1 < a_2 <$$...$$< a_M \leq N-1$
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Input
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Input is given from Standard Input in the following format:
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N M
a_1
a_2
.
.
.
a_M翻译中…
Output
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Print the number of ways to climb up the stairs under the condition, modulo $1\ 000\ 000\ 007$.
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样例
Input #1
6 1
3
Output #1
4
There are four ways to climb up the stairs, as follows:
- $0 \to 1 \to 2 \to 4 \to 5 \to 6$
- $0 \to 1 \to 2 \to 4 \to 6$
- $0 \to 2 \to 4 \to 5 \to 6$
- $0 \to 2 \to 4 \to 6$
Input #2
10 2
4
5
Output #2
0
There may be no way to climb up the stairs without setting foot on the broken steps.
Input #3
100 5
1
23
45
67
89
Output #3
608200469
Be sure to print the count modulo $1\ 000\ 000\ 007$.
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。