关于筛法

 1 int cnt;
 2 int prime[MAXN];
 3 int pri[MAXN];
 4 int phi[MAXN];
 5 int miu[MAXN];
 6 
 7 /* 素数筛 */
 8 void pre_prime(){
 9     mem(prime,0);
10     cnt = 0;
11     prime[0] = prime[1] = 1;
12     for(int i = 2 ; i < MAXN ; i++){
13         if(!prime[i]) pri[cnt++] = i;
14         for(int j = 0 ; j < cnt && i * pri[j] <= MAXN ; j++){
15             prime[i * pri[j]] = 1;
16             if(i % pri[j] == 0) break;
17         }
18     }
19 }
20 /* 莫比乌斯筛 */
21 void pre_miu(){
22     mem(prime,0);
23     cnt = 0;
24     miu[1] = 1;
25     for(int i = 2 ; i < MAXN ; i++){
26         if(!prime[i]){
27             miu[i] = -1;
28             pri[cnt++] = i;
29         }
30         for(int j = 0 ; j < cnt && i * pri[j] <= MAXN ; j++){
31             prime[i * pri[j]] = 1;
32             if(i % pri[j] == 0){
33                 miu[i * pri[j]] = 0;
34                 break;
35             }else miu[i * pri[j]] = -miu[i];
36         }
37     }
38 }
39 /* 欧拉筛 */
40 void pre_phi(){
41     mem(prime,0);
42     cnt = 0;
43     phi[1] = 1;
44     for(int i = 2 ; i < MAXN ; i++){
45         if(!prime[i]){
46             miu[i] = -1;
47             pri[cnt++] = i;
48         }
49         for(int j = 0 ; j < cnt && i * pri[j] <= MAXN ; j++){
50             prime[i * pri[j]] = 1;
51             if(i % pri[j] == 0){
52                 phi[i * pri[j]] = phi[i] * pri[j];
53                 break;
54             }else phi[i * pri[j]] = phi[i] * (pri[j] - 1);
55         }
56     }
57 }