hdu2824(欧拉函数+打表)

The Euler function

Time Limit: 2000/1000 MS (Java/Others)    Memory Limit: 32768/32768 K (Java/Others)
Total Submission(s): 4624    Accepted Submission(s): 1935

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
  
  

解题思路：欧拉函数打表，刚开始把打表放在while循环里面，超时了几次，

下次注意啊：把打表函数放在循环外执行！

#include<stdio.h>
#include<string.h>
#define MAX 3000001
long long a[MAX];
int m,n;
void oula()
{
	int i,j;
	memset(a,0,sizeof(a));
	a[1]=1;
	for(i=2;i<MAX;i++)
	{
		if(!a[i])
		{
			for(j=i;j<MAX;j+=i)
			{
				if(!a[j])
				  a[j]=j;
				a[j]=a[j]/i*(i-1);
			}
		}
	}
}
int main()
{
   oula();
   long long sum;
   int m,n;
   while(scanf("%d%d",&m,&n)!=EOF)
   {
   	   sum=0;
   	   for(int i=m;i<=n;i++)
   	    sum+=a[i];
   printf("%lld\n",sum);
   }
 return 0;	
}