poj2187Beauty Contest(凸包直径）

链接

利用旋转卡壳

参考博客http://www.cppblog.com/staryjy/archive/2010/09/25/101412.html

 #include <iostream>
 #include<cstdio>
 #include<cstring>
 #include<algorithm>
 #include<stdlib.h>
 #include<vector>
 #include<cmath>
 #include<queue>
 #include<set>
 using namespace std;
 #define N 50010
 #define LL long long
 #define INF 0xfffffff
 const double eps = 1e-;
 const double pi = acos(-1.0);
 const double inf = ~0u>>;
 struct point
 {
     int x,y;
     point(int x=,int y = ):x(x),y(y){}
 }p[N],ch[N];
 typedef point pointt;
 pointt operator - (point a,point b)
 {
     return point(a.x-b.x,a.y-b.y);
 }
 int dcmp(double x)
 {
     if(fabs(x)<eps) return ;
     return x<?-:;
 }
 double cross(point a,point b)
 {
     return 1.0*a.x*b.y-a.y*b.x;
 }
 double mul(point p0,point p1,point p2)
 {
     return cross(p1-p0,p2-p0);
 }
 int dis(point a)
 {
     return a.x*a.x+a.y*a.y;
 }
 bool cmp(point a,point b)
 {
     if(dcmp(mul(p[],a,b))==) return dis(a-p[])<dis(b-p[]);
     return dcmp(mul(p[],a,b))>;
 }
 int graham(int n)
 {
     int i,k=,top;
     point tmp;
     for(i = ;  i< n; i++)
     {
         if(p[i].y<p[k].y||(p[i].y==p[k].y&&p[i].x<p[k].x))
             k = i;
     }
     if(k!=)
         swap(p[],p[k]);
     sort(p+,p+n,cmp);
     ch[] = p[];
     ch[] = p[];
     top = ;
     for(i = ; i < n; i++)
     {
         while(top>&&dcmp(mul(ch[top-],ch[top],p[i]))<=)
             top--;
         ch[++top] = p[i];
     }
     return top;
 }
 int rotating_calipers(int n)
 {
     int q = ;
     int ans = ;
     ch[n] = ch[];
     for(int i =  ; i < n;  i++)
     {
         while(mul(ch[i+],ch[q+],ch[i])>mul(ch[i+],ch[q],ch[i]))
         q = (q+)%n;
         ans = max(ans,max(dis(ch[i]-ch[q]),dis(ch[i+]-ch[q+])));
     }
     return ans;
 }
 int main()
 {
     int n,i;
     while(scanf("%d",&n)!=EOF)
     {
         for(i = ; i < n;i++)
         scanf("%d%d",&p[i].x,&p[i].y);
         int top = graham(n);
         int ans = rotating_calipers(top+);
         printf("%d\n",ans);
     }
     return ;
 }