51 Nod 1244 莫比乌斯函数前n项和

#include<bits/stdc++.h>
using namespace std;
const int maxn=1e6+10;
typedef long long ll;
map<ll,ll> ma;
int check[maxn],prime[maxn],mu[maxn];
void Mobius(int N)//莫比乌斯函数线性筛
{
    int pos=0;mu[1]=1;
    for (int i = 2 ; i <= N ; i++)
    {
        if (!check[i])
            prime[pos++] = i,mu[i]=-1;
        for (int j = 0 ; j < pos && i*prime[j] <= N ; j++)
        {
            check[i*prime[j]] = 1;
            if (i % prime[j] == 0)
            {
                mu[i*prime[j]]=0;
                break;
            }
            mu[i*prime[j]]=-mu[i];
        }
    }
    for(int i=2;i<=N;i++)
        mu[i]+=mu[i-1];
}
ll solve(ll a)
{
    if(a<=1e6)     //记忆化
        return mu[a];
    if(ma.count(a))
        return ma[a];
    ll temp=1;
    for(ll i=2;i<=a;)
    {
        ll t=a/i;
        ll k=a/t;
        temp-=(k-i+1)*solve(t);//分段或者叫分块加速一下
        i=k+1;
    }
    return ma[a]=temp;
}
int main()
{
    Mobius(1e6);
    ll a,b;
    cin>>a>>b;
    cout<<solve(b)-solve(a-1)<<endl;
}