【莫比乌斯反演】BZOJ1101 [POI2007]Zap

#include<cstdio>
#include<algorithm>
using namespace std;
typedef long long ll;

const int maxn=50005,N=maxn-5;
int q,K,mu[maxn],sum[maxn],p[maxn];
bool vis[maxn];
void prepare(){
mu[1]=1;
for (int i=2;i<=N;i++){
if (!vis[i]) p[++p[0]]=i,mu[i]=-1;
for (int j=1;j<=p[0],i*p[j]<=N;j++){
vis[i*p[j]]=1;
if (i%p[j]==0) {mu[i*p[j]]=0;break;}
else mu[i*p[j]]=-mu[i];
}
}
for (int i=1;i<=N;i++) sum[i]=sum[i-1]+mu[i];
}
ll get(int n,int m){
n/=K;m/=K;
if (n>m) swap(n,m);
ll res=0;
for (int d=1,lst=0;d<=n;d=lst+1){
lst=min(n/(n/d),m/(m/d));
res+=(ll)(sum[lst]-sum[d-1])*(n/d)*(m/d);
}
return res;
}
int main(){
scanf("%d",&q);
prepare();
while (q--){
int a,b;
scanf("%d%d%d",&a,&b,&K);
printf("%lld\n",get(a,b));
}
return 0;
}