【莫比烏斯反演】BZOJ1101 [POI2007]Zap

題面在這裏

沒什麼好說的，反演裸題

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;
}