bzoj 3994: [SDOI2015]约数个数和

本蒟蒻不会23333（SDOI总是这种sb题，感觉很快就回家“耕耘”了。）

%%%fqk      http://blog.csdn.net/phenix_2015/article/details/50790860

#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 mo[N],prime[N],f[N],cnt;
LL d[N];
bool vis[N];
void mobius()
{
    mo[1]=d[1]=1;
    for (int i=2; i<=50000; i++)
    {
        if (!vis[i]) prime[++cnt]=i,mo[i]=-1,d[i]=2,f[i]=1;
        for (int j=1; j<=cnt && i*prime[j]<=50000; j++)
        {
            vis[prime[j]*i]=1;
            if (i%prime[j])
            {
                mo[i*prime[j]]=-mo[i];
                f[i*prime[j]]=1;
                d[i*prime[j]]=d[i]*2;
            }
            else
            {
                mo[i*prime[j]]==0;
                f[i*prime[j]]=f[i]+1;
                d[i*prime[j]]=d[i]/(f[i]+1)*(f[i]+2);
            }
        }
    }
    for (int i=1; i<=50000; i++) d[i]+=d[i-1],mo[i]+=mo[i-1];
}
int main()
{
    mobius(); int T=ra();
    while (T--)
    {
        int n=ra(),m=ra(); if (n>m) swap(n,m);
        LL ans=0;
        for (int i=1,pos; i<=n; i=pos+1)
        {
            pos=min(n/(n/i),m/(m/i));
            ans+=(LL)(mo[pos]-mo[i-1])*d[n/i]*d[m/i];
        }
        printf("%lld
",ans);
    }
    return 0;
}