省选专练【SDOI2012】longgie问题

莫比乌斯反演。

是NOI2010能量采集的翻版

#include<iostream>
#include<cstdio>
#include<algorithm>
#include<cmath>
#include<cstring>
using namespace std;
typedef int INT;
#define ll long long
#define int ll
ll phi(ll x){
	ll ret=x;
	for(int i=2;i*i<=x;i++){
		if(x%i==0){
			ret=ret*(i-1)/i;
		}
		while(x%i==0){
			x/=i;
		}
	}
//	cout<<x<<" "<<ret<<endl;
	if(x>1){
		ret=ret*(x-1)/x;
	}
	return ret;
}
INT main(){
	ll n;
//	cout<<phi(7)<<endl;
	scanf("%lld",&n);
	ll ans=0;
	for(int i=1;i*i<=n;i++){
		if(n%i==0){
			ans+=i*(phi(n/i));
			if((n/i)!=i){
				ans+=(n/i)*phi(i);
			}
		}
	}
	cout<<ans<<endl;
}

转载于:https://www.cnblogs.com/Leo-JAM/p/10079293.html