先给出点的个数N,2<=N<=100000,再给出坐标Xi,Yi.(-10000.0<=xi,yi<=10000.0)
#include
#include
#include
#include
#include
using namespace std;
const int maxn=500010;
const double eps=1e-12;
struct point
{
double x,y;
point() {}
point(double a,double b){x=a,y=b;}
}p[maxn],O;
int n;
double v[10][10],R;
point calc(point a,point b,point c)
{
v[1][1]=2*b.x-2*a.x;
v[1][2]=2*b.y-2*a.y;
v[1][3]=b.x*b.x-a.x*a.x+b.y*b.y-a.y*a.y;
v[2][1]=2*c.x-2*b.x;
v[2][2]=2*c.y-2*b.y;
v[2][3]=c.x*c.x-b.x*b.x+c.y*c.y-b.y*b.y;
int i,j,k;
for(i=1;i<=2;i++)
{
for(j=i+1;j<=2;j++) if(fabs(v[j][i])>fabs(v[i][i])) for(k=i;k<=3;k++) swap(v[i][k],v[j][k]);
double tmp=v[i][i];
for(k=i;k<=3;k++) v[i][k]/=tmp;
for(j=1;j<=2;j++) if(i!=j) for(tmp=v[j][i],k=i;k<=3;k++) v[j][k]-=tmp*v[i][k];
}
point ret(v[1][3],v[2][3]);
return ret;
}
double dis(point a,point b)
{
return sqrt((a.x-b.x)*(a.x-b.x)+(a.y-b.y)*(a.y-b.y));
}
int main()
{
scanf("%d",&n);
int i,j,k;
for(i=1;i<=n;i++) scanf("%lf%lf",&p[i].x,&p[i].y);
random_shuffle(p+1,p+n+1);
O=p[1],R=0;
for(i=2;i<=n;i++) if(dis(O,p[i])>R+eps)
{
O=p[i],R=0;
for(j=1;jR+eps)
{
O=point((p[i].x+p[j].x)/2,(p[i].y+p[j].y)/2),R=dis(O,p[i]);
for(k=1;kR+eps)
O=calc(p[i],p[j],p[k]),R=dis(O,p[k]);
}
}
printf("%.2lf\n%.2lf %.2lf",R,O.x,O.y);
return 0;
}