HDU 1286：找新朋友（欧拉函数）

 1 #include <cstdio>
 2 #include <cstring>
 3 #include <algorithm>
 4 using namespace std;
 5 #define N 33000
 6 int is_prime[N], prime[N], phi[N];
 7 
 8 void Euler() {
 9     int n = 32767;
10     phi[1] = 0; int cnt = 0;
11     for(int i = 2; i <= n; i++) {
12         if(!is_prime[i]){
13             prime[++cnt] = i; phi[i] = i - 1;
14         }
15         for(int j = 1; j <= cnt && i * prime[j] <= n; j++) {
16             is_prime[i * prime[j]] = 1;
17             if(i % prime[j] == 0) {
18                 phi[i * prime[j]] = phi[i] * prime[j];
19                 break;
20             }
21             phi[i * prime[j]] = phi[i] * phi[prime[j]];
22         }
23     }
24 }
25 
26 int main() {
27     int t;
28     scanf("%d", &t);
29     Euler();
30     while(t--) {
31         int n;
32         scanf("%d", &n);
33         printf("%d\n", phi[n]);
34     }
35     return 0;
36 }