三行写出莫比乌斯函数(HDU1695)

莫比乌斯函数是可以在三行内写出来的

#include<bits/stdc++.h>
using namespace std;
typedef long long ll;
const int maxn=1000000;
int mu[maxn+10],T;
void Mobius(){
    for(int d=1,k;d<=maxn;++d)
        for(mu[1]=1,k=d<<1;k<=maxn;mu[k]=mu[k]-mu[d],k+=d);
    for(int i=1;i<=maxn;++i)mu[i]+=mu[i-1];
}
int main(){
    Mobius();
    ios::sync_with_stdio(false);
    cin>>T;
    for(int kase=1,a,b,c,d,k;kase<=T;++kase){
        cin>>a>>b>>c>>d>>k;
        if(!k){
            cout<<"Case "<<kase<<": 0"<<endl;
            continue;
        }
        b/=k;d/=k;
        if(b>d)b^=d^=b^=d;
        ll ans1=0,ans2=0;
        for(int i=1,t;i<=b;i=t+1){
            t=min(b/(b/i),d/(d/i));
            ans1+=1ll*(mu[t]-mu[i-1])*(b/i)*(d/i);
        }
        for(int i=1,t;i<=b;i=t+1){
            t=b/(b/i);
            ans2+=1ll*(mu[t]-mu[i-1])*(b/i)*(b/i);
        }
        ans1-=ans2/2;
        cout<<"Case "<<kase<<": "<<ans1<<endl;
    }
}