HDU 2824:The Euler function【Euler】

The Euler function

Time Limit: 2000/1000 MS (Java/Others)    Memory Limit: 32768/32768 K (Java/Others)
Total Submission(s): 4509    Accepted Submission(s): 1873

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
   
   
   
   

 

老是调用函数会超时，，，累加打表可解决～～；

AC-code:

#include<cstdio>
#define MAX 3000010
long long E[MAX];
void euler()
{
	int j,i;
	for(i=2;i<MAX;i++)
	{
		if(!E[i])
		for(j=i;j<MAX;j+=i)
		{
			if(!E[j])
				E[j]=j;
			E[j]=E[j]/i*(i-1);
		}
		E[i]+=E[i-1];
	}
}
int main()
{
	int a,b;
	euler();
	while(~scanf("%d%d",&a,&b))
	{
		printf("%lld\n",E[b]-E[a-1]);
	}
	return 0;
}