Beauty Contest(凸包求最远点)

http://poj.org/problem?id=2187

题意：求凸包上最远点距离的平方

思路：开始用旋转卡壳求的最远点，WA，改了好久。。后来又改成枚举凸包上的点。。AC了。。

 #include <stdio.h>
 #include <algorithm>
 #include <math.h>
 using namespace std;
 const int N=;
 int n;
 struct Point
 {
     int x,y;
     Point(int x = ,int y = ):x(x),y(y) {}
     bool friend operator < (const Point &a,const Point &b)
     {
         return a.x < b.x||(a.x==b.x&&a.y < b.y);
     }

 } p[N],ch[N];
 typedef Point Vector;
 Vector operator-(Point a,Point b)
 {
     return Vector(a.x-b.x,a.y-b.y);
 }
 int Cross(Vector A,Vector B)
 {
     return A.x*B.y-A.y*B.x;
 }
 int Distance(Point a,Point b)
 {
     return (a.x-b.x)*(a.x-b.x)+(a.y-b.y)*(a.y-b.y);
 }
 int Graham()//判断凸包
 {
     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;
 }
 int main()
 {
     scanf("%d",&n);
     for (int i = ; i < n; i++)
         scanf("%d %d",&p[i].x,&p[i].y);
     int cnt = Graham();
     int ans = ;
     for (int i = ; i < cnt ; i++)
     {
         for (int j = ; j < i; j++)
         {
             int dis = Distance(ch[i],ch[j]);
             ans = max(ans,dis);
         }
     }
     printf("%d\n",ans);
     return ;
 }

旋转卡壳的那段代码，不知道哪错了，先保留着吧。。后期再改。。

 int dia_rotating_calipers(int cnt)//旋转卡壳
 {
     int dia = ;
     int  q = ;
     for (int i = ; i < cnt; i++)
     {
         while(Cross(ch[i+]-ch[i],ch[q+]-ch[i]) > Cross(ch[i+]-ch[i],ch[q]-ch[i]))
             q = (q+)%n;
         dia = max(dia,max(Distance(ch[i],ch[q]),Distance(ch[i+],ch[q+])));
     }
     return dia;
 }