bzoj 1101: [POI2007]Zap

Posted 2020-09-01 ws_ccd

裸的莫比乌斯反演

 1 #include<bits/stdc++.h>
 2 #define N 100005
 3 #define M 10000005
 4 #define LL long long
 5 #define inf 0x3f3f3f3f
 6 using namespace std;
 7 inline int ra()
 8 {
 9     int x=0,f=1; char ch=getchar();
10     while (ch<‘0‘ || ch>‘9‘) {if (ch==‘-‘) f=-1; ch=getchar();}
11     while (ch>=‘0‘ && ch<=‘9‘) {x=x*10+ch-‘0‘; ch=getchar();}
12     return x*f;
13 }
14 int a,b,c,d,n,ans,cnt;
15 int mo[N],prime[N],sum[N];
16 bool vis[N];
17 void mobius()
18 {
19     mo[1]=1;
20     for (int i=2; i<=50005; i++)
21     {
22         if (!vis[i]) prime[++cnt]=i,mo[i]=-1;
23         for (int j=1; j<=cnt && i*prime[j]<=50005; j++)
24         {
25             vis[i*prime[j]]=1;
26             if (i%prime[j]) mo[i*prime[j]]=-mo[i];
27             else {mo[i*prime[j]]=0; break;}
28         }
29     }
30     for (int i=1; i<=50005; i++)
31         sum[i]=sum[i-1]+mo[i];
32 }
33 int main()
34 {
35     n=ra(); mobius();
36     while (n--)
37     {
38         a=ra(); b=ra(); d=ra();
39         a/=d; b/=d; ans=0;
40         for (int i=1,pos; i<=min(a,b); i=pos+1)
41         {
42             pos=min(a/(a/i),b/(b/i));
43             ans+=(sum[pos]-sum[i-1])*(a/i)*(b/i);
44         }
45         printf("%d\n",ans);  //cout<<ans  RE.......
46     }
47 }