[51nod1244]莫比乌斯函数之和

裸杜教筛板子。

#include <iostream>
#include <cstdio>
#include <map>
using namespace std;
typedef long long ll;
const int N=7000000;
map<ll,ll>ph,mu;
int prime[N>>3],tot;short miu[N];
bool vis[N];
void init() {
    miu[1]=1;
    for(int i=2;i<=N-5;i++) {
        if(!vis[i]) prime[++tot]=i,miu[i]=-1;
        for(int j=1;j<=tot&&prime[j]*i<=N-5;j++) {
            vis[i*prime[j]]=1;
            if(i%prime[j]==0) break;
            miu[i*prime[j]]=-miu[i];
        }
    }
    for(int i=1;i<=N-5;i++) miu[i]+=miu[i-1];
}
ll solvemiu(ll x) {
    if(x<=N-5) return miu[x];
    if(mu.count(x)) return mu[x];
    ll ans=1;
    for(ll i=2ll,nxti;i<=x;i=nxti) {
        nxti=x/(x/i)+1ll;
        ans-=(nxti-i)*solvemiu(x/i);
    }
    return mu[x]=ans;
}
int main() {
    init();
    long long l,r;
    cin>>l>>r;
    cout<<solvemiu(r)-solvemiu(l-1)<<endl;
}