欧拉函数模板

 1 #include <iostream>
 2 using namespace std;
 3 
 4 int phi( int n )
 5 {
 6     int ans = n;
 7     for ( int i = 2; i * i <= n; i++ )
 8     {
 9         if ( n % i == 0 )
10         {
11             ans -= ans / i;
12             do
13             {
14                 n = n / i;
15             } while ( n % i == 0 );
16         }
17     }
18     if ( n != 1 )
19     {
20         ans -= ans / n;
21     }
22     return ans;
23 }
24 
25 int pphi( int n )
26 {
27     int ans = 1;
28     for ( int i = 2; i * i <= n; i++ )
29     {
30         if ( n % i == 0 )
31         {
32             ans *= i - 1;
33             n = n / i;
34             while ( n % i == 0 )
35             {
36                 ans *= i;
37                 n = n / i;
38             }
39         }
40     }
41     if ( n != 1 )
42     {
43         ans *= n - 1;
44     }
45     return ans;
46 }
47 
48 int main()
49 {
50     int t;
51     cin >> t;
52     while ( t-- )
53     {
54         int n;
55         cin >> n;
56         cout << pphi(n) << endl;
57     }
58     return 0;
59 }

 1 #include <iostream>
 2 using namespace std;
 3 
 4 const int N = 32768;
 5 int phi[N];
 6 
 7 void init()
 8 {
 9     phi[0] = phi[1] = 1;
10     for ( int i = 2; i < N; i++ )
11     {
12         phi[i] = i;
13     }
14     for ( int i = 2; i < N; i++ )
15     {
16         if ( phi[i] == i )
17         {
18             phi[i]--;
19             for ( int j = i + i; j < N; j += i )
20             {
21                 phi[j] -= phi[j] / i;
22             }
23         }
24     }
25 }
26 
27 int main()
28 {
29     init();
30     int t;
31     cin >> t;
32     while ( t-- )
33     {
34         int n;
35         cin >> n;
36         cout << phi[n] << endl;
37     }
38     return 0;
39 }