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  • B

    Given a positive integer N, your task is to calculate the sum of the positive integers less than N which are not coprime to N. A is said to be coprime to B if A, B share no common positive divisors except 1.

    Input

    For each test case, there is a line containing a positive integer N(1 ≤ N ≤ 1000000000). A line containing a single 0 follows the last test case.

    Output

    For each test case, you should print the sum module 1000000007 in a line.

    Sample Input

    3
    4
    0

    Sample Output

    0
    2

    用个互斥原理就可以了

    #include<iostream>
    #include<stdio.h>
    #include<stdlib.h>
    #include<cmath>
    #include<string.h>
    #include<algorithm>
    #define sf scanf
    #define pf printf
    //#define cl clear()
    #define pb push_back
    #define mm(a,b) memset((a),(b),sizeof(a))
    #include<vector>
    typedef __int64 ll;
    typedef long double ld;
    const ll mod=1e9+7;
    using namespace std;
    vector< int >v;
    const double pi=acos(-1.0);
    ll cal(ll x,ll n)
    {
    	if(x==n) return 0;
    	int a=(n-1)/x;
    	return (x*a+(x*a*(a-1))/2)%mod;
    }
    ll solve(ll n)
    {
    	ll x=n;
    	for(int i=2;i*i<=x;i++)
    	{
    	//	cout<<"1"<<endl;
    		if(x%i==0)
    		{
    			v.pb(i);
    			while(x%i==0)
    			{
    				x/=i;
    			 } 
    		}
    	}
    	if(x>1) v.pb(x);
    	ll sum=0;
    	for(int i=1;i<(1<<v.size()) ;i++)
    	{
    		ll bits=0,ans=1;
    		for(int j=0;j<v.size() ;j++)
    		{
    			if((1<<j)&i)
    			{
    				bits++;
    				ans*=v[j];
    			}
    		}
    		if(bits&1)
    		sum=(sum+cal(ans,n))%mod;
    		else
    		{
    			sum=(sum-cal(ans,n));
    			while(sum<0)
    			sum+=mod;
    		}
    	}
    	return sum;
    }
    int main()
    {
    //	freopen("output1.txt", "r", stdin);
    	ll n;
    	while(1)
    	{
    		v.clear();
    		sf("%I64d",&n);
    		if(n==0) return 0;
    		pf("%I64d
    ",solve(n));
    	}
    }
    
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  • 原文地址:https://www.cnblogs.com/wzl19981116/p/9355156.html
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