hdu2824 The Euler function O(n)求欧拉函数

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 }