【莫比乌斯反演】BZOJ1101 [POI2007]Zap

题面在这里

没什么好说的，反演裸题

示例程序：

#include<cstdio>#include<algorithm>using namespace std;typedef long long ll;const int maxn=50005,N=maxn-5;int q,K,mu[maxn],sum[maxn],p[maxn];bool vis[maxn];void prepare(){    mu[1]=1;    for (int i=2;i<=N;i++){        if (!vis[i]) p[++p[0]]=i,mu[i]=-1;        for (int j=1;j<=p[0],i*p[j]<=N;j++){            vis[i*p[j]]=1;            if (i%p[j]==0) {mu[i*p[j]]=0;break;}             else mu[i*p[j]]=-mu[i];        }    }    for (int i=1;i<=N;i++) sum[i]=sum[i-1]+mu[i];}ll get(int n,int m){    n/=K;m/=K;    if (n>m) swap(n,m);    ll res=0;    for (int d=1,lst=0;d<=n;d=lst+1){        lst=min(n/(n/d),m/(m/d));        res+=(ll)(sum[lst]-sum[d-1])*(n/d)*(m/d);    }    return res;}int main(){    scanf("%d",&q);    prepare();    while (q--){        int a,b;        scanf("%d%d%d",&a,&b,&K);        printf("%lld\n",get(a,b));    }    return 0;}