In mathematics you don't understand things, you just get used to them.

DescriptionLink.给你一个序列,你每次可以取 $1\sim3$ 个数然后计算和,问你对于每一种和,方案数是多少。Solution设一个 OGF $A(x)=\sum_{i=0}^{...

DescriptionLink.给出一个数列,要求将其分成几段,使每段的和非严格递增,求最小的每段的和的平方和。Solution注意到 $a_{i}$ 为正,对于正数有这样的结论:$$ a^{2...