The Euler function
Time Limit: 2000/1000 MS (Java/Others) Memory Limit: 32768/32768 K (Java/Others)Total Submission(s): 8579 Accepted Submission(s): 3598
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
#include <stdio.h>
#define Max 3000001
typedef long long ll;
using namespace std;
ll euler[Max];
void Init()
{
euler[1]=1;
for(int i=2;i<Max;i++)
euler[i]=i;
for(int i=2;i<Max;i++)
if(euler[i]==i)
for(int j=i;j<Max;j+=i)
euler[j]=euler[j]/i*(i-1);
//先进行除法是为了防止中间数据的溢出,以上就是打表
for(int i=2;i<Max;i++)
euler[i]+=euler[i-1];
//将[1,i-1]的和叠加到euler[i]上可以节省一个数组,这句根据题意的改变
}
int main()
{
Init();
int a,b;
while(~scanf("%d %d",&a,&b))
{
printf("%I64d\n",euler[b]-euler[a-1]);
}
return 0;
}