poj2187(最远点的距离的平方)

#include<cstdio>
#include<cstring>
#include<iostream>
#include<algorithm>
#include<cmath>
#include<vector>

using namespace std;

const double pi=acos(-1.0);

const double eps=1e-8;

int cmp(double x)
{
if(fabs(x)<eps)
return 0;
if(x>0)
return 1;
return -1;
}

inline double sqr(double x)
{
return x*x;
}

struct point
{
double x,y;
point() {}
point(double a,double b):x(a),y(b){}
friend point operator + (const point &a,const point &b)
{
return point(a.x+b.x,a.y+b.y);
}
friend point operator - (const point &a,const point &b)
{
return point(a.x-b.x,a.y-b.y);
}
friend bool operator == (const point &a,const point &b)
{
return cmp(a.x-b.x)==0&&cmp(a.y-b.y)==0;
}
friend point operator * (const point &a,const double &b)
{
return point(a.x*b,a.y*b);
}
friend point operator * (const double &a,const point &b)
{
return point(a*b.x,a*b.y);
}
friend point operator / (const point &a,const double &b)
{
return point(a.x/b,a.y/b);
}
double norm()
{
return sqrt(sqr(x)+sqr(y));
}
};

double det(const point &a,const point &b)//cha
{
return a.x*b.y-a.y*b.x;
}
double dot(const point &a,const point &b)
{
return a.x*b.x+a.y*b.y;
}
double dist(const point &a,const point &b)
{
return (a-b).norm();
}
point rotate_point(const point &p,double A)//ni
{
double tx=p.x,ty=p.y;
return point(tx*cos(A)-ty*sin(A),tx*sin(A)+ty*cos(A));
}

struct polygon_convex
{
vector<point> P;
polygon_convex(int Size=0)
{
P.resize(Size);
}
};

bool cmp_less(const point &a,const point &b)
{
return cmp(a.x-b.x)<0||cmp(a.x-b.x)==0&&cmp(a.y-b.y)<0;
}

polygon_convex convex_hull(vector<point> a)
{
polygon_convex res(2*a.size()+5);
sort(a.begin(),a.end(),cmp_less);
a.erase(unique(a.begin(),a.end()),a.end());
int m=0;
for(int i=0;i<a.size();i++)
{
while(m>1 && cmp(det(res.P[m-1]-res.P[m-2],a[i]-res.P[m-2]))<=0)
--m;
res.P[m++]=a[i];
}
int k=m;
for(int i=int(a.size())-2;i>=0;i--)
{
while(m>k && cmp(det(res.P[m-1]-res.P[m-2],a[i]-res.P[m-2]))<=0)
--m;
res.P[m++]=a[i];
}
res.P.resize(m);
if(a.size()>1)
res.P.resize(m-1);
return res;
}

double convex_diameter(polygon_convex &a,int &First,int &Second)
{
vector<point>  &p=a.P;
int n=p.size();
double maxd=0.0;
if(n==1)
{
First=Second=0;
return maxd;
}
#define next(i) ((i+1)%n)
for(int i=0,j=1;i<n;i++)
{
while(cmp(det(p[next(i)]-p[i],p[j]-p[i])-det(p[next(i)]-p[i],p[next(j)]-p[i]))<0)
{
j=next(j);
}
double d=dist(p[i],p[j]);
if(d>maxd)
{
maxd=d;
First=i,Second=j;
}
d=dist(p[next(i)],p[next(j)]);
if(d>maxd)
{
maxd=d;
First=i,Second=j;
}
}
return maxd;
}

vector<point> tt;
int main()
{
int n;
while(scanf("%d",&n)!=EOF)
{
tt.clear();
for(int i=0;i<n;i++)
{
double tx,ty;
scanf("%lf%lf",&tx,&ty);
tt.push_back(point(tx,ty));
}
polygon_convex xx=convex_hull(tt);
int ans1,ans2;
double ans=convex_diameter(xx,ans1,ans2);
printf("%.0lf\n",ans*ans);
}
return 0;
}