Codeforces Round 236 (Div. 1)
D
Beautiful Pairs of Numbers
Codeforces
2300
原题
← CE →
翻译中…

The sequence of integer pairs $(*a*_{1}, *b*_{1}), (*a*_{2}, *b*_{2}), ..., (*a*_{*k*}, *b*_{*k*})$ is beautiful, if the following statements are fulfilled:

翻译中…
  • $1 ≤ *a*_{1} ≤ *b*_{1} < *a*_{2} ≤ *b*_{2} < ... < *a*_{*k*} ≤ *b*_{*k*} ≤ *n*$, where $*n*$ is a given positive integer;
  • all numbers $*b*_{1} - *a*_{1}$, $*b*_{2} - *a*_{2}$, $...$, $*b*_{*k*} - *a*_{*k*}$ are distinct.
翻译中…

For the given number $*n*$ find the number of beautiful sequences of length $*k*$. As the answer can be rather large, print the remainder after dividing it by $1000000007$ $(10^{9} + 7)$.

翻译中…

Input

翻译中…

The first line contains integer $*t*$ ($1 ≤ *t* ≤  2·10^{5}$) — the number of the test data.

翻译中…

Each of the next $*t*$ lines contains two integers $*n*$ and $*k*$ ($1 ≤ *k* ≤ *n* ≤ 1000$).

翻译中…

Output

翻译中…

For each test from the input print the answer to the problem modulo $1000000007$ $(10^{9} + 7)$. Print the answers to the tests in the order in which the tests are given in the input.

翻译中…

Note

翻译中…

In the first test sample there is exactly one beautiful sequence: $(1, 1)$.

翻译中…

In the second test sample, the following sequences are beautiful:

翻译中…
  • $(1, 1)$;
  • $(1, 2)$;
  • $(2, 2)$.
翻译中…

In the fourth test sample, the following sequences are beautiful:

翻译中…
  • $(1, 1)$;
  • $(1, 2)$;
  • $(1, 3)$;
  • $(2, 2)$;
  • $(2, 3)$;
  • $(3, 3)$.
翻译中…

In the fifth test sample, the following sequences are beautiful:

翻译中…
  • $(1, 1), (2, 3)$;
  • $(1, 2), (3, 3)$.
翻译中…

In the third and sixth samples, there are no beautiful sequences.

翻译中…

样例

Input #1
6
1 1
2 1
2 2
3 1
3 2
3 3
Output #1
1
3
0
6
2
0
InputCopy OutputCopy
题目信息
题号
403D
时间限制
3 s
内存限制
256 MB
标签
组合数学
动态规划

题面与样例版权归 Codeforces 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。