学步园

传送门:http://www.lydsy.com/JudgeOnline/problem.php?id=2154

题解:http://www.cnblogs.com/jianglangcaijin/archive/2013/11/27/3446169.html

Rank里时间分成了200ms-900ms和3000ms+两大波

似乎有更优做法?有待研究

Code:

#include<cstdio>
#include<iostream>
#include<algorithm>
#include<vector>
using namespace std;
const int maxn=1e7+5;
typedef long long LL;
int MOD=20101009;
int n,m;
bool p[maxn];
int prime[maxn];
LL u[maxn];
void init(int maxn){
	u[1]=1;
	for(int i=2;i<maxn;i++){
		if(!p[i]){
			prime[++prime[0]]=i;u[i]=-1;
		}for(int j=1;j<=prime[0]&&i*prime[j]<maxn;j++){
			p[i*prime[j]]=1;
			if(i%prime[j]==0){
				u[i*prime[j]]=0;break;
			}else u[i*prime[j]]=-u[i];
		}
	}for(int i=2;i<maxn;i++)u[i]=(u[i-1]+(LL)(i*u[i]%MOD*i))%MOD;
}
inline LL S(LL n,LL m){
	LL ans=0;
	if(n>m)swap(n,m);
	for(int i=1,last;i<=n;i=last+1){
		last=min(n/(n/i),m/(m/i));
		LL Sum=(n/i*(n/i+1)/2%MOD)*(m/i*(m/i+1)/2%MOD)%MOD;
		ans=(ans+(LL)(u[last]-u[i-1])*Sum%MOD)%MOD;
	}return ans;
}
int main(){
	cin>>n>>m;
	LL ans=0;
	if(n>m)swap(n,m);
	init(m+1);
	for(int i=1,last;i<=n;i=last+1){
		last=min(n/(n/i),m/(m/i));
		ans=(ans+(LL)(i+last)*(last-i+1)/2*(S(n/i,m/i)))%MOD;
	}while(ans<0)ans+=MOD;
	cout<<ans%MOD<<endl;
	return 0;
}