BZOJ 1101 Zap

莫比乌斯反演裸题。

#include<iostream>
#include<cstdio>
#include<cstring>
#include<cmath>
#define maxn 50050
using namespace std;
int n,a,b,d,pre[maxn],miu[maxn],prime[maxn],cnt=0;
bool vis[maxn];
void make_table()
{
    miu[1]=1;
    for (int i=2;i<=maxn;i++)
    {
        if (vis[i]==false) 
        {
            prime[++cnt]=i;
            miu[i]=-1;
        }
        for (int j=1;j<=cnt && i*prime[j]<=maxn;j++)
        {
            vis[i*prime[j]]=true;
            if (i%prime[j]!=0) miu[i*prime[j]]=-miu[i];
            else 
            {
                miu[i*prime[j]]=0;
                break;
            }
        }
    }
    for (int i=1;i<=maxn;i++)
        pre[i]=pre[i-1]+miu[i];
}
int find(int a,int b,int d)
{
    int i=1,ans=0;
    if (a>b) swap(a,b);
    while (i<=(a/d))
    {
        int j;
        if ((a/(i*d)==0) || (b/(i*d)==0)) j=0;
        else j=min((a/d)/((a/d)/i),(b/d)/((b/d)/i));
        ans+=(pre[j]-pre[i-1])*(a/(i*d))*(b/(i*d));
        i=j+1;
    }
    return ans;
}
void work()
{
    scanf("%d%d%d",&a,&b,&d);
    printf("%d\n",find(a,b,d));
}
int main()
{
    scanf("%d",&n);
    make_table();
    for (int i=1;i<=n;i++)
        work();
    return 0;
}