uva 11168 - Airport

凸包+一点直线的知识；

 #include <cstdio>
 #include <cmath>
 #include <cstring>
 #include <algorithm>
 #include <vector>
 #define eps 1e-9
 using namespace std;
 const double pi = acos(-);

 int dcmp(double x)
 {
     return fabs(x) < eps ?  : (x >  ?  : -);
 }

 struct Point
 {
     double x;
     double y;

     Point(double x = , double y = ):x(x), y(y) {}

     bool operator < (const Point& e) const
     {
         return dcmp(x - e.x) <  || (dcmp(x - e.x) ==  && dcmp(y - e.y) < );
     }

     bool operator == (const Point& e) const
     {
         return dcmp(x - e.x) ==  && dcmp(y - e.y) == ;
     }
 };

 typedef Point Vector;

 Vector operator + (Point A, Point B)
 {
     return Vector(A.x + B.x, A.y + B.y);
 }

 Vector operator - (Point A, Point B)
 {
     return Vector(A.x - B.x, A.y - B.y);
 }

 Vector operator * (Point A, double p)
 {
     return Vector(A.x * p, A.y * p);
 }

 Vector operator / (Point A, double p)
 {
     return Vector(A.x / p, A.y / p);
 }

 double cross(Point a,Point b){return a.x*b.y-a.y*b.x;}
 Point rotate(Point a,double ang){return Point(a.x*cos(ang)-a.y*sin(ang),a.x*sin(ang)+a.y*cos(ang));}
 int convexhull(Point *p,int n,Point *ch)
 {
     sort(p,p+n);
     int m=;
     for(int i=;i<n;i++)
     {
         while(m>&&cross(ch[m-]-ch[m-],p[i]-ch[m-])<=)m--;
         ch[m++]=p[i];
     }
     int k=m;
     for(int i=n-;i>=;i--)
     {
         while(m>k&&cross(ch[m-]-ch[m-],p[i]-ch[m-])<=)m--;
         ch[m++]=p[i];
     }
     if(n>)m--;
     return m;
 }
 Point p[],ch[];

 int main()
 {
     int t,n,ca=;
     scanf("%d",&t);
     while(t--)
     {
         double sumx=;
         double sumy=;
         scanf("%d",&n);
         for(int i=;i<n;i++)
         {
             scanf("%lf%lf",&p[i].x,&p[i].y);
             sumx+=p[i].x;
             sumy+=p[i].y;
         }
         printf("Case #%d: ",ca++);
         double mi=99999999999.0;
         int m=convexhull(p,n,ch);
         for(int i=;i<m;i++)
         {
             double a=-ch[(i+)%m].y+ch[i].y;
             double b=ch[(i+)%m].x-ch[i].x;
             double c=ch[i].x*ch[(i+)%m].y-ch[i].y*ch[(i+)%m].x;
             double d=fabs(a*sumx+b*sumy+c*n)/sqrt(a*a+b*b);
             mi=min(mi,d);
         }
         printf("%.3lf\n",n>?mi/n:);
     }
     return ;
 }