The Euler function

Time Limit: 2000/1000 MS (Java/Others)    Memory Limit: 32768/32768 K (Java/Others)

Total Submission(s): 3674    Accepted Submission(s): 1509

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

 

总结：最初，我用sum[i]数组存储1到i的欧拉函数值得和，但是因为开了两个数组，超了空间，本想用此法优化时间的，结果还是要从a循环到b取每个数的欧拉函数的值相加

1 #include
       
         2 #include
        
          3 __int64 euler[3000000]; 4 int main() 5 { 6     __int64 ans; 7     memset(euler,0,sizeof(euler)); 8     euler[1] = 1; 9     int a,b,i,j;10     for(i = 2; i <3000000; i++)11     {12         if(!euler[i])13             for(j = i; j <3000000; j += i)14             {15                 if(!euler[j])16                     euler[j] = j;17                 euler[j] = euler[j]/i*(i-1);18             }19     }20     while(scanf("%d%d",&a,&b)!=EOF)21     {22         ans=0;23         for(i=a; i<=b; i++)24             ans+=euler[i];25         printf("%I64d\n",ans);26     }27     return 0;28 }