hdu2824 The Euler function O(n)求欧拉函数

 1 #include <bits/stdc++.h> 
 2 #define ll long long 
 3 using namespace std ; 
 4 
 5 const int N = 3000011 ; 
 6 int l,r ; 
 7 int prime[ 300011 ],phi[N] ;  
 8 ll sum ; 
 9 bool f[N] ; 
10 
11 inline void Euler_init(int NN)  
12 {
13     phi[ 1 ] = 1 ; f[ 1 ] = 1 ; 
14     prime[ 0 ] = 0 ; 
15     for(int i=2;i<=NN;i++) 
16     {
17         if( !f[ i ] ) prime[++prime[0]] = i,phi[ i ] = i-1 ; 
18         for(int j=1;j<=prime[ 0 ] && i*prime[ j ]<=NN;j++) 
19         {
20             f[ i*prime[ j ] ] = 1 ; 
21             if( i%prime[ j ] == 0 ) 
22             {
23                 phi[ i*prime[ j ] ] = phi[ i ] * prime[ j ] ; 
24                 break ; 
25             }
26             else phi[ i*prime[ j ] ] = phi[ i ] * (prime[ j ]-1) ; 
27         }
28     }
29 }
30 
31 int main() 
32 {
33     Euler_init(3000000) ;   
34     
35     while(~scanf("%d%d",&l,&r)) 
36     {
37         sum = 0 ; 
38         for(int i=l;i<=r;i++) 
39             sum = sum + phi[ i ] ; 
40         printf("%lld\n",sum) ; 
41     }    
42     return 0 ; 
43 }