Hdu 3694 Fermat Point in Quadrangle（三分）

#include<cstdio>
#include<cstring>
#include<iostream>
#include<algorithm>
using namespace std;
const double eps=1e-7;
struct Node
{
double x,y;
};
Node a[5];
double minx,maxx,miny,maxy;
double dist(double x,double y)
{
double sum=0;
for(int i=0;i<4;i++)
sum+=sqrt((a[i].x-x)*(a[i].x-x)+(a[i].y-y)*(a[i].y-y));
return sum;
}
double checky(double x)
{
double ly,ry,midy,midmidy;
ly=miny,ry=maxy,midy=(ly+ry)/2.0;
while(ry-ly>eps)
{
midy=(ly+ry)/2.0;
midmidy=(midy+ry)/2.0;
if(dist(x,midy)<dist(x,midmidy))
ry=midmidy;
else ly=midy;
}
return dist(x,midy);
}
int main()
{
while(scanf("%lf%lf%lf%lf%lf%lf%lf%lf",&a[0].x,&a[0].y,&a[1].x,&a[1].y,&a[2].x,&a[2].y,&a[3].x,&a[3].y)==8)
{
if(a[0].x<0) break;
minx=a[0].x,maxx=a[0].x;
miny=a[0].y,maxy=a[0].y;
for(int i=0;i<4;i++)
{
minx=min(minx,a[i].x);
maxx=max(maxx,a[i].x);
miny=min(miny,a[i].y);
maxy=max(maxy,a[i].y);
}
double lx,rx,midx,midmidx;
lx=minx,rx=maxx,midx=(lx+rx)/2.0;
while(rx-lx>eps)
{
midx=(lx+rx)/2.0;
midmidx=(midx+rx)/2.0;
if(checky(midx)<checky(midmidx))
rx=midmidx;
else lx=midx;
// cout<<midx<<endl;
}
//cout<<midx<<endl;
printf("%.4f\n",checky(midx));
}
return 0;
}