bzoj 1101 [POI2007]Zap——反演

题目：https://www.lydsy.com/JudgeOnline/problem.php?id=1101

#include<cstdio>
#include<cstring>
#include<algorithm>
#define ll long long
using namespace std;
const int N=5e4+5;
int T,n,m,D,u[N],pri[N];bool vis[N];
int rdn()
{
  int ret=0;bool fx=1;char ch=getchar();
  while(ch>'9'||ch<'0'){if(ch=='-')fx=0;ch=getchar();}
  while(ch>='0'&&ch<='9')ret=ret*10+ch-'0',ch=getchar();
  return fx?ret:-ret;
}
void init()
{
  int lm=5e4,cnt=0;u[1]=1;
  for(int i=2;i<=lm;i++)
    {
      if(!vis[i])pri[++cnt]=i,u[i]=-1;
      for(int j=1;j<=cnt&&(ll)i*pri[j]<=lm;j++)
    {
      vis[i*pri[j]]=1;
      if(i%pri[j]==0){u[i*pri[j]]=0;break;}
      u[i*pri[j]]=-u[i];
    }
      u[i]+=u[i-1];
    }
}
int main()
{
  T=rdn();init();
  while(T--)
    {
      n=rdn();m=rdn();D=rdn();
      n/=D;m/=D;if(n>m)swap(n,m);
      ll ans=0;
      for(int i=1,d0,d1,j;i<=n;i=j+1)
    {
      d0=n/i;d1=m/i; j=min(n/d0,m/d1);
      ans+=(ll)(u[j]-u[i-1])*d0*d1;
    }
      printf("%lld\n",ans);
    }
  return 0;
}