[整除分块] 2020牛客多校H.Dividing

题目

思路

见大佬博客->添加链接描述

代码

#include<bits/stdc++.h>
#define ll long long
using namespace std;
const ll mod=1e9+7;
int main(){
	ios::sync_with_stdio(false);cin.tie(0);cout.tie(0);
	ll n,k;
	cin>>n>>k;
	ll l=2,res=0,r;
	for(l=2;l<=n&&l<=k;l=r+1){
		r=min((n/(n/l)),k);
		res=(res+((r-l+1)%mod*(n/l)%mod)%mod)%mod;
	}
	r=l=2;
	for(l=2;l<=n-1&&l<=k;l=r+1){
		r=min(((n-1)/((n-1)/l)),k);
		res=(res+((r-l+1)%mod*((n-1)/l)%mod)%mod)%mod;
		l=r+1;
	}
	cout<<(n+res+k-1)%mod<<endl;
    return 0;
}