[HDU]2848 The Euler function[欧拉函数][水题]

最新推荐文章于 2019-08-12 00:07:28 发布

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最新推荐文章于 2019-08-12 00:07:28 发布

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分类专栏：欧拉函数水题文章标签：欧拉函数

本文链接：https://blog.youkuaiyun.com/ctsas/article/details/55522734

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欧拉函数

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本文介绍了一种计算从a到b区间内所有整数的欧拉函数之和的算法。通过预先计算并存储每个整数的欧拉函数值，实现了快速求解。此算法适用于数论领域的研究和竞赛。

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Problem Description
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

#include<stdio.h>
#define MAX_N 3000100
int phi[MAX_N];

void init(){
    for(int i=1;i<MAX_N;i++) phi[i]=i;
    for(int i=2;i<MAX_N;i++)
        if(phi[i]==i)
            for(int j=i;j<MAX_N;j+=i)
                phi[j]=phi[j]/i*(i-1);
}

int main()
{
    init();int a,b;
    while(~scanf("%d%d",&a,&b)){
        long long ans=0;
        for(int i=a;i<=b;i++)
            ans+=phi[i];
        printf("%lld\n",ans);
    }
    return 0;
}