hdu 6158 计算几何

#include<bits/stdc++.h>using namespace std;const double eps=1e-13;const double PI=acos(-1.0);int main(){    int t,r1,r2,n;    scanf("%d",&t);    while(t--&&scanf("%d%d%d",&r1,&r2,&n)!=EOF)    {        if(r1<r2)             swap(r1,r2);        double k1=-1.0/r1,k2=1.0/r2,k3=1.0/(r1-r2);        double k4=k1 + k2 + k3;        double ans=(r1-r2)*(r1-r2);        n--;        for(int i=1;i<=n;i+=2)        {            double r4=1.0/k4;            if(r4*r4<eps)                break;            ans+=r4*r4;            if(i+1<=n)                 ans+=r4*r4;            double k5=2*(k1+k2+k4)-k3;            k3=k4;            k4=k5;        }        printf("%.5f\n",ans*PI);    }    return 0;}