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 0;
    return x<0?-1:1;
}

struct Point{
    int x,y;
    Point(int x=0 , int y=0):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 == 0) return a.x<b.x;
    else return v>0;
}

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[0] = a[0] , rec[1] = a[1];
    top=1;
    for(int i=2 ; i<n ; i++){
        while(top>0 && Cross(rec[top]-rec[top-1] , a[i]-rec[top-1])<=0)
            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-1 ; i>=0 ; i--){
        while(top>tmp && Cross(rec[top]-rec[top-1] , a[i]-rec[top-1])<=0)
            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-1 , p=0 , q=0;
    int maxn = 0;
    for(p=0 ; p<top ; p++){
        while(Cross(a[p]-a[la] , a[q+1]-a[la]) - Cross(a[p]-a[la] , a[q]-a[la])>0)
            q=(q+1)%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=0 ; i<n ; i++) po[i].input();
        p = po[0];
        for(int i=1 ;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 0;
}