hdu 3007 Buried memory 最远点对

  1 #include<iostream>
  2 #include<cstdio>
  3 #include<cstring>
  4 #include<cstdlib>
  5 #include<cmath>
  6 #include<algorithm>
  7 #include<vector>
  8 #define inf 0x7fffffff
  9 #define exp 1e-10
 10 #define PI 3.141592654
 11 using namespace std;
 12 const int maxn=500+10;
 13 
 14 int n;
 15 struct Point
 16 {
 17     double x,y;
 18     Point(double x=0,double y=0):x(x),y(y){}
 19 }an[maxn],bn[maxn];
 20 typedef Point Vector;
 21 double dcmp(double x)
 22 {
 23     if (fabs(x)<exp) return 0;
 24     return x<0 ? -1 : 1;
 25 }
 26 Vector operator + (Vector A,Vector B) {return Vector(A.x+B.x , A.y+B.y); }
 27 Vector operator - (Vector A,Vector B) {return Vector(A.x-B.x , A.y-B.y); }
 28 Vector operator * (Vector A,double p) {return Vector(A.x*p , A.y*p); }
 29 Vector operator / (Vector A,double p) {return Vector(A.x/p , A.y/p); }
 30 bool operator < (Point a,Point b) {return a.x<b.x || (a.x==b.x && a.y<b.y); }
 31 bool operator == (Point a,Point b) {return dcmp(a.x-b.x)==0 && dcmp(a.y-b.y)==0; }
 32 
 33 double Dot(Vector A,Vector B) {return A.x*B.x + A.y*B.y ; }
 34 double Length(Vector A,Vector B) {return sqrt(Dot(A,A)); }
 35 double cross(Vector A,Vector B) {return A.x*B.y - B.x*A.y; }
 36 
 37 double dist(Point A,Point B)
 38 {
 39     double xx=(A.x-B.x)*(A.x-B.x);
 40     double yy=(A.y-B.y)*(A.y-B.y);
 41     return sqrt(xx+yy);
 42 }
 43 
 44 Point cur;
 45 double rotating_calipers(Point *ch,int n)
 46 {
 47     int q=1;
 48     double ans=-1;
 49     cur.x=cur.y=0;
 50     ch[n]=ch[0];
 51     for (int p=0 ;p<n ;p++)
 52     {
 53         while (cross(ch[q+1]-ch[p+1],ch[p]-ch[p+1])>cross(ch[q]-ch[p+1],ch[p]-ch[p+1]))
 54             q=(q+1)%n;
 55         double len=dist(ch[p],ch[q]);
 56         double len2=dist(ch[p+1],ch[q+1]);
 57         if (len>ans+exp)
 58         {
 59             ans=len;
 60             cur.x=(ch[p].x+ch[q].x)/2.0;
 61             cur.y=(ch[p].y+ch[q].y)/2.0;
 62         }
 63         if (len2>ans+exp)
 64         {
 65             ans=len2;
 66             cur.x=(ch[p+1].x+ch[q+1].x)/2.0;
 67             cur.y=(ch[p+1].y+ch[q+1].y)/2.0;
 68         }
 69     }
 70     return ans;
 71 }
 72 
 73 int Convexhull(Point *p,int n,Point *ch)
 74 {
 75     sort(p,p+n);
 76     int m=0;
 77     for (int i=0 ;i<n ;i++)
 78     {
 79         while (m>1 && dcmp(cross(ch[m-1]-ch[m-2],p[i]-ch[m-2]))<0) m--;
 80         ch[m++]=p[i];
 81     }
 82     int k=m;
 83     for (int i=n-2 ;i>=0 ;i--)
 84     {
 85         while (m>k && dcmp(cross(ch[m-1]-ch[m-2],p[i]-ch[m-2]))<0) m--;
 86         ch[m++]=p[i];
 87     }
 88     if (n>1) m--;
 89     return m;
 90 }
 91 
 92 int main()
 93 {
 94     while (scanf("%d",&n)!=EOF && n)
 95     {
 96         for (int i=0 ;i<n ;i++) scanf("%lf%lf",&an[i].x,&an[i].y);
 97         if (n==1) {printf("%.2lf %.2lf 0.00\n",an[0].x,an[0].y);continue; }
 98         if (n==2) {printf("%.2lf %.2lf %.2lf\n",(an[0].x+an[1].x)/2.0,
 99             (an[0].y+an[1].y)/2.0,dist(an[0],an[1])/2.0);continue; }
100         int m=Convexhull(an,n,bn);
101         double ans=rotating_calipers(bn,m);
102         printf("%.2lf %.2lf %.2lf\n",cur.x,cur.y,ans/2.0);
103     }
104     return 0;
105 }