2017 多校训练第六场 HDU 6097 Mindis

#include <bits/stdc++.h>
using namespace std;
// #define test TEST

int main(int argc, char const *argv[])
{
#ifdef test
freopen("test.txt","r",stdin);
#endif
int T;
scanf("%d",&T);
while(T--){
double r,a,b,c,d;
scanf("%lf %lf %lf %lf %lf",&r,&a,&b,&c,&d);
double rr=sqrt(a*a+b*b);
double k=r*r/(rr*rr);
double aa=k*a,bb=k*b,cc=k*c,dd=k*d;
double dislen=(aa*dd-bb*cc)/sqrt((cc-aa)*(cc-aa)+(dd-bb)*(dd-bb));
if(fabs(dislen)<=r){//反演点的连线与圆有交点
printf("%.7f\n",sqrt((a*r/rr-c*r/rr)*(a*r/rr-c*r/rr)+(b*r/rr-d*r/rr)*(b*r/rr-d*r/rr)));
// printf("%.7f\n",sqrt((aa-cc)*(aa-cc)+(bb-dd)*(bb-dd)));
continue;
}
//最优值在中垂线上取到
double diss=sqrt((a-c)*(a-c)+(b-d)*(b-d));
double t=r-sqrt(rr*rr-diss*diss/4);
double ans=sqrt(diss*diss/4+t*t)*2;
printf("%.7f\n",ans);
}
return 0;
}