【HDU 5733】tetrahedron

#include <cstdio>
#include <cmath>
#define dd double
struct point{
	dd x,y,z;
	int input(){
		return scanf("%lf%lf%lf",&x,&y,&z);
	}
	point operator -(const point &b) const
	{
		return (point){x-b.x,y-b.y,z-b.z};
	}
	dd operator *(const point &b)const
	{
		return x*b.x+y*b.y+z*b.z;
	}
	point operator ^(const point &b)const
	{
		return (point){y*b.z-b.y*z,b.x*z-x*b.z,x*b.y-b.x*y};
	}
}p[5];
dd sqr(dd x){
	return x*x;
}
dd area(const point &o,const point &s,const point &e,point &n){
	point a=s-o,b=e-o;
	n=a^b;
	return sqrt(sqr(n.x)+sqr(n.y)+sqr(n.z))/2;
}
int main() {
	while(~p[1].input()){
		for(int i=2;i<=4;i++)
			p[i].input();
		dd s[5];
		point n,l=p[1]-p[2];;
		s[1]=area(p[2],p[3],p[4],n);
		if(l*n==0){
			puts("O O O O");
			continue;
		}
		s[2]=area(p[1],p[3],p[4],n);
		s[3]=area(p[1],p[2],p[4],n);
		s[4]=area(p[1],p[2],p[3],n);
		dd x=0,y=0,z=0,down=0;
		for(int i=1;i<=4;i++){
			down+=s[i];
			x+=s[i]*p[i].x;
			y+=s[i]*p[i].y;
			z+=s[i]*p[i].z;
		}
		point a=(point){x/down,y/down,z/down};
		point b=a-p[1];
		dd r=fabs(b*n)/s[4]/2;
		printf("%.4f %.4f %.4f %.4f\n",a.x,a.y,a.z,r);
	}
}