【BZOJ】【P2045】【双亲数】【题解】【莫比乌斯反演】

传送门:http://www.lydsy.com/JudgeOnline/problem.php?id=2045

这题就是zap……

n/=d,m/=d然后

Code:

#include<cstdio>#include<iostream>#include<algorithm>#include<cctype>using namespace std;const int maxn=1e6+5;typedef long long LL;LL n,m,d;LL prime[maxn],p[maxn],u[maxn];void get_mu(){u[1]=1;for(LL i=2;i<=m;i++){if(!p[i]){prime[++prime[0]]=i;u[i]=-1;}for(LL j=1;i*prime[j]<=n&&j<=prime[0];j++){p[i*prime[j]]=1;if(i%prime[j]==0){u[i*prime[j]]=0;break;}else u[i*prime[j]]=-u[i];}}for(LL i=2;i<=m;i++)u[i]+=u[i-1];}int main(){cin>>n>>m>>d;n/=d;m/=d;if(n>m)swap(n,m);get_mu();LL ans=0,pos=0;for(LL i=1;i<=n;){pos=min(n/(n/i),m/(m/i));ans+=(u[pos]-u[i-1])*(n/i)*(m/i);i=pos+1;}cout<<ans<<endl;return 0;}