The Tower（ccpc吉林）

http://acm.hdu.edu.cn/contests/contest_showproblem.php?pid=1005&cid=867

#include<iostream>
#include<cstring>
#include<algorithm>
#include<cstdio>
#include<cmath>
using namespace std;
int main(){
    int t;
    scanf("%d",&t);
    int sign=1;
    while(t--){
        double r,h;
        scanf("%lf%lf",&r,&h);
        double tanx=h/r;
        double x0,y0,z0,xv,yv,zv;
        scanf("%lf%lf%lf%lf%lf%lf",&x0,&y0,&z0,&xv,&yv,&zv);
        double a=xv*xv+yv*yv-zv*zv/(tanx*tanx);
        double b=2.0*(x0*xv+y0*yv+zv*r/tanx-z0*zv/(tanx*tanx));
        double c=x0*x0+y0*y0-r*r+2.0*z0*r/tanx-z0*z0/(tanx*tanx);
        double fuck=fabs(b*b-4.0*a*c);
        double ans1=(-b+sqrt(fuck))/(2.0*a);
        double ans2=(-b-sqrt(fuck))/(2.0*a);
        double ans;
        double z1=z0+zv*ans1;
        double z2=z0+zv*ans2;
        if(z1<=h&&z1>=0&&z2<=h&&z2>=0){
            ans=min(ans1,ans2);
        }
        else if(z1<=h&&z1>=0){
            ans=ans1;
        }
        else
            ans=ans2;
        printf("Case %d: %.10lf\n",sign++,ans);
    }
    return 0;
}