poj 2187 N个点中输出2点的最大距离的平方

旋转卡壳

Sample Input

4
0 0
0 1
1 1
1 0
Sample Output

2

 # include <iostream>
 # include <cstdio>
 # include <cstring>
 # include <algorithm>
 # include <string>
 # include <cmath>
 # include <queue>
 # define LL long long
 using namespace std ;

 struct Point
 {
     int x,y;
     Point(int _x = ,int _y = )
     {
         x = _x; y = _y;
     }
     Point operator -(const Point &b)const
     {
         return Point(x - b.x, y - b.y);
     }
     int operator ^(const Point &b)const
     {
         return x*b.y - y*b.x;
     }
     int operator *(const Point &b)const
     {
         return x*b.x + y*b.y;
     }
     void input()
     {
         scanf("%d%d",&x,&y);
     }
 };
 //距离的平方
 int dist2(Point a,Point b)
 {
     return (a-b)*(a-b);
 }
 //******二维凸包，int***********
 const int MAXN = ;
 Point list[MAXN];
 int Stack[MAXN],top;
 bool _cmp(Point p1,Point p2)
 {
     int tmp = (p1-list[])^(p2-list[]);
     if(tmp > )return true;
     else if(tmp ==  && dist2(p1,list[]) <= dist2(p2,list[]))
     return true;
     else return false;
 }
 void Graham(int n)
 {
     Point p0;
     int k = ;
     p0 = list[];
     for(int i = ;i < n;i++)
         if(p0.y > list[i].y || (p0.y == list[i].y && p0.x > list[i].x))
         {
             p0 = list[i];
             k = i;
         }
     swap(list[k],list[]);
     sort(list+,list+n,_cmp);
     if(n == )
     {
         top = ;
         Stack[] = ;
         return;
     }
     if(n == )
     {
         top = ;
         Stack[] = ; Stack[] = ;
         return;
     }
     Stack[] = ; Stack[] = ;
     top = ;
     for(int i = ;i < n;i++)
     {
         while(top >  &&
         ((list[Stack[top-]]-list[Stack[top-]])^(list[i]-list[Stack[top-]])) <= )
         top--;
         Stack[top++] = i;
     }
 }
 //旋转卡壳，求两点间距离平方的最大值
 int rotating_calipers(Point p[],int n)
 {
     int ans = ;
     Point v;
     int cur = ;
     for(int i = ;i < n;i++)
     {
         v = p[i]-p[(i+)%n];
         while((v^(p[(cur+)%n]-p[cur])) < )
            cur = (cur+)%n;
         ans = max(ans,max(dist2(p[i],p[cur]),dist2(p[(i+)%n],p[(cur+)%n])));
     }
     return ans;
 }
 Point p[MAXN];
 int main()
 {
     //freopen("in.txt","r",stdin) ;
     int n;
     while(scanf("%d",&n) == )
     {
         for(int i = ;i < n;i++)
             list[i].input();
         Graham(n);
         for(int i = ;i < top;i++)p[i] = list[Stack[i]];
         printf("%d\n",rotating_calipers(p,top));
     }
     return ;
 }