摘要：
先要推式子 $$ \begin{aligned} \varphi(x)\varphi(y)&=(x\prod_{p|x}\frac{p 1}p)(y\prod_{p|y}\frac{p 1}p)\\ &=(\prod_{p|xy}\frac{p 1}p)(\prod_{p|\gcd(x,y)}\fr 阅读全文
摘要：
"TheLostWeak" ~~讲解得十分清楚，就不造轮子了~~ cpp include define ll long long define ls (x L[N]; int val[N 1; build(ls,l,mid); build(rs,mid+1,r); val[x]=min(val[ls 阅读全文