HDU 2824(The Euler function)欧拉函数

最新推荐文章于 2019-09-03 21:18:17 发布

Eknight123

最新推荐文章于 2019-09-03 21:18:17 发布

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The Euler function phi is an important kind of function in number theory, (n) represents the amount of the numbers which are smaller than n and coprime to n, and this function has a lot of beautiful characteristics. Here comes a very easy question: suppose you are given a, b, try to calculate (a)+ (a+1)+....+ (b)

Input

There are several test cases. Each line has two integers a, b (2<a<b<3000000).

Output

Output the result of (a)+ (a+1)+....+ (b)

Sample Input

3 100

Sample Output

题意：输入两个数，求解这个区间欧拉函数值之和

数据不大直接打表输出

#include<bits/stdc++.h>
#define LL long long
#define maxn 3000010
using namespace std;
LL phi[maxn];
int main()
{
    ios::sync_with_stdio(false),cin.tie(0),cout.tie(0);
    for(int i=2;i<maxn;i++)
    {
        phi[i]=i;
    }
    for(int i=2;i<maxn;i++)
    {
        if(phi[i]==i)
        {
            for(int j=i;j<maxn;j+=i)
            {
                phi[j]=phi[j]/i*(i-1);
            }
        }
    }
    LL l,r;
    while(cin>>l>>r)
    {
       LL ans=0;
       for(int i=l;i<=r;i++)
       {
          ans+=phi[i];
       }
       cout<<ans<<endl;
    }
    return 0;
}

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