hdu 2824(欧拉函数)

Posted 2020-07-13 AC菜鸟机

The Euler function

Time Limit: 2000/1000 MS (Java/Others)    Memory Limit: 32768/32768 K (Java/Others)
Total Submission(s): 5235    Accepted Submission(s): 2225

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<a<b<3000000).

 

 

Output

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

 

 

Sample Input

3 100

 

 

Sample Output

3042

 

欧拉函数模板题，不能开两个数组，会超时。

#include <stdio.h>
#include <string.h>
#include <algorithm>
#include <iostream>
#include <math.h>
using namespace std;
typedef long long LL;
const int N =3000005;
LL euler[N];
//LL sum[N];
void getEuler()
{
    memset(euler,0,sizeof(euler));
    euler[1] = 1;
    for(int i = 2; i <= N; i++){
        if(!euler[i])
            for(int j = i; j <= N; j+= i)
            {
                if(!euler[j])
                    euler[j] = j;
                euler[j] = euler[j]/i*(i-1);
            }
        //sum[i]=sum[i-1]+(LL)euler[i];
    }
}

int main()
{
    getEuler();
    int a,b;
    while(~scanf("%d%d",&a,&b)){
        LL sum = 0;
        for(int i=a;i<=b;i++){
            sum+=euler[i];
        }
        printf("%lld\n",sum);
    }
    return 0;
}