【莫比乌斯反演】BZOJ1101 [POI2007]zap

 1 #include<cstdio>
 2 #include<algorithm>
 3 #include<cstring>
 4 using namespace std;
 5 const int maxn=5e4+5;
 6 
 7 int flag[maxn],prime[maxn],cnt;
 8 int mu[maxn],sum[maxn];
 9 
10 int getmu(){
11     mu[1]=1;
12     for(int i=2;i<maxn;i++){
13         if(!flag[i]){
14             prime[++cnt]=i;
15             mu[i]=-1;
16         }
17         for(int j=1;i*prime[j]<maxn&&j<=cnt;j++){
18             flag[i*prime[j]]=1;
19             if(i%prime[j]==0){
20                 mu[i*prime[j]]=0;
21                 break;
22             }
23             mu[i*prime[j]]=-mu[i];
24         }
25     }
26     for(int i=1;i<maxn;i++)
27         sum[i]=sum[i-1]+mu[i];
28 }
29 
30 int cal(int n,int m){
31     int ret=0,pos;
32     if(n>m) swap(n,m);
33     for(int i=1;i<=n;i=pos+1){
34         pos=min(n/(n/i),m/(m/i));
35         ret+=(sum[pos]-sum[i-1])*(n/i)*(m/i);
36     }
37     return ret;
38 }
39 
40 int main(){
41     int T,a,b,d;
42     scanf("%d",&T);
43     getmu();
44     
45     while(T--){
46         scanf("%d%d%d",&a,&b,&d);
47         a/=d,b/=d;
48         printf("%d\n",cal(a,b));
49     }
50     return 0;
51 }