AtCoder Beginner Contest 156
E
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原题
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Problem Statement

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There is a building with $n$ rooms, numbered $1$ to $n$.

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We can move from any room to any other room in the building.

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Let us call the following event a move: a person in some room $i$ goes to another room $j~ (i \neq j)$.

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Initially, there was one person in each room in the building.

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After that, we know that there were exactly $k$ moves happened up to now.

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We are interested in the number of people in each of the $n$ rooms now. How many combinations of numbers of people in the $n$ rooms are possible?

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Find the count modulo $(10^9 + 7)$.

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Constraints

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  • All values in input are integers.
  • $3 \leq n \leq 2 \times 10^5$
  • $2 \leq k \leq 10^9$
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Input

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Input is given from Standard Input in the following format:

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n k

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Output

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Print the number of possible combinations of numbers of people in the $n$ rooms now, modulo $(10^9 + 7)$.

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样例

Input #1
3 2
Output #1
10
Let $c_1$, $c_2$, and $c_3$ be the number of people in Room $1$, $2$, and $3$ now, respectively. There are $10$ possible combination of $(c_1, c_2, c_3)$: - $(0, 0, 3)$ - $(0, 1, 2)$ - $(0, 2, 1)$ - $(0, 3, 0)$ - $(1, 0, 2)$ - $(1, 1, 1)$ - $(1, 2, 0)$ - $(2, 0, 1)$ - $(2, 1, 0)$ - $(3, 0, 0)$ For example, $(c_1, c_2, c_3)$ will be $(0, 1, 2)$ if the person in Room $1$ goes to Room $2$ and then one of the persons in Room $2$ goes to Room $3$.
Input #2
200000 1000000000
Output #2
607923868
Print the count modulo $(10^9 + 7)$.
Input #3
15 6
Output #3
22583772
题目信息
题号
abc156_e
时间限制
2 s
内存限制
1024 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。