POJ 2187 求凸包上最长距离

简单的旋转卡壳题目

以每一条边作为基础，找到那个最远的对踵点，计算所有对踵点的点对距离

这里求的是距离的平方，所有过程都是int即可

 #include <iostream>
 #include <cstdio>
 #include <cstring>
 #include <cstdlib>
 #include <cmath>
 #include <algorithm>
 using namespace std;
 #define N 50010
 #define eps 1e-9
 int n , top;

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

 struct Point{
     int x,y;
     Point(int x= , int y=):x(x),y(y){}
     bool operator==(const Point &m) const{
         return x==m.x&&y==m.y;
     }
     int squaredDis(){return x*x+y*y;}
     void input(){scanf("%d%d" , &x , &y);}
     void print(){cout<<x<<" "<<y<<endl;}
 }po[N] , rec[N] , p;
 typedef Point Vector;

 Vector operator+(Vector a , Vector b){return Vector(a.x+b.x , a.y+b.y);}
 Vector operator-(Vector a , Vector b){return Vector(a.x-b.x , a.y-b.y);}
 Vector operator*(Vector a , double b){return Vector(a.x*b , a.y*b);}
 Vector operator/(Vector a , double b){return Vector(a.x/b , a.y/b);}

 int Cross(Vector a , Vector b){return a.x*b.y-b.x*a.y;}
 double Len(Vector a){return sqrt(a.x*a.x*1.0+a.y*a.y);}

 bool cmp(Point a , Point b){
     int v = Cross(a , b);
     if(v == ) return a.x<b.x;
     else return v>;
 }

 void Graham(Point *a , Point *rec)
 {
     sort(a , a+n , cmp);
   //  for(int i=0 ; i<n ; i++) cout<<i<<" "<<a[i].x<< " "<<a[i].y<<endl;
     rec[] = a[] , rec[] = a[];
     top=;
     for(int i= ; i<n ; i++){
         while(top> && Cross(rec[top]-rec[top-] , a[i]-rec[top-])<=)
             top--;
         rec[++top] = a[i];
     }
    // for(int i=0 ; i<=top ; i++) cout<<i<<" "<<rec[i].x<< " "<<rec[i].y<<endl;
     int tmp = top;
     for(int i=n- ; i>= ; i--){
         while(top>tmp && Cross(rec[top]-rec[top-] , a[i]-rec[top-])<=)
             top--;
         rec[++top]=a[i];
     }
   //  for(int i=0 ; i<=top ; i++) cout<<i<<" "<<rec[i].x<< " "<<rec[i].y<<endl;
 }

 int maxDis(Point *a)
 {
     int la=top- , p= , q=;
     int maxn = ;
     for(p= ; p<top ; p++){
         while(Cross(a[p]-a[la] , a[q+]-a[la]) - Cross(a[p]-a[la] , a[q]-a[la])>)
             q=(q+)%top;
         maxn = max(maxn , (a[q]-a[la]).squaredDis());
         maxn = max(maxn , (a[q]-a[p]).squaredDis());
         la = p;
     }
     return maxn;
 }

 int main()
 {
    // freopen("a.in" , "r" , stdin);
     while(~scanf("%d" , &n))
     {
         for(int i= ; i<n ; i++) po[i].input();
         p = po[];
         for(int i= ;i<n ; i++)
             if(po[i].y<p.y||(po[i].y==p.y&&po[i].x<p.x)) p=po[i];
         Graham(po , rec);
         int ans = maxDis(rec);
         cout<<ans<<endl;
     }
     return ;
 }