HDU 5793 A Boring Question 多校训练
摘要：
There are an equation. ∑0≤k1,k2,⋯km≤n∏1⩽j<m(kj+1kj)%1000000007=?∑0≤k1,k2,⋯km≤n∏1⩽j<m(kj+1kj)%1000000007=? We define that (kj+1kj)=kj+1!kj!(kj+1−kj)!(k 阅读全文
posted @ 2018-01-21 22:04 九月旧约 阅读(170) 评论(0) 推荐(0) 编辑
