bzoj 1101: [POI2007]Zap

裸的莫比乌斯反演

#include<bits/stdc++.h>
#define N 100005
#define M 10000005
#define LL long long
#define inf 0x3f3f3f3f
using namespace std;
inline int ra()
{
    int x=0,f=1; char ch=getchar();
    while (ch<'0' || ch>'9') {if (ch=='-') f=-1; ch=getchar();}
    while (ch>='0' && ch<='9') {x=x*10+ch-'0'; ch=getchar();}
    return x*f;
}
int a,b,c,d,n,ans,cnt;
int mo[N],prime[N],sum[N];
bool vis[N];
void mobius()
{
    mo[1]=1;
    for (int i=2; i<=50005; i++)
    {
        if (!vis[i]) prime[++cnt]=i,mo[i]=-1;
        for (int j=1; j<=cnt && i*prime[j]<=50005; j++)
        {
            vis[i*prime[j]]=1;
            if (i%prime[j]) mo[i*prime[j]]=-mo[i];
            else {mo[i*prime[j]]=0; break;}
        }
    }
    for (int i=1; i<=50005; i++)
        sum[i]=sum[i-1]+mo[i];
}
int main()
{
    n=ra(); mobius();
    while (n--)
    {
        a=ra(); b=ra(); d=ra();
        a/=d; b/=d; ans=0;
        for (int i=1,pos; i<=min(a,b); i=pos+1)
        {
            pos=min(a/(a/i),b/(b/i));
            ans+=(sum[pos]-sum[i-1])*(a/i)*(b/i);
        }
        printf("%d
",ans);  //cout<<ans  RE.......
    }
}