算法复习——凸包加旋转卡壳（poj2187）

#include<iostream>
#include<cstdio>
#include<cstdlib>
#include<cmath>
#include<cctype>
#include<cstring>
#include<string>
#include<ctime>
#include<algorithm>
using namespace std;
struct point 
{
  int x;
  int y;
}p[50005],q[50005];
inline int operator*(point a,point b)
{
  return a.x*b.y-a.y*b.x;
}
inline point operator-(point a,point b)
{
  point t;
  t.x=a.x-b.x;
  t.y=a.y-b.y;
  return t;
}
inline int norm(point a)
{
  return a.x*a.x+a.y*a.y;
}
bool comp(int u,int v)
{
  int det=(p[u]-p[1])*(p[v]-p[1]);
  if(det!=0)  return det>0;
  return norm(p[u]-p[1])<norm(p[v]-p[1]);
}
int n,m;
int next(int i)
{
  if(i!=m)  return ++i;
  else return 1;
}
void tubao()
{
  int id=1;
  for(int i=2;i<=n;i++)
    if(p[id].x>p[i].x||(p[id].x==p[i].x&&p[id].y>p[i].y))
      id=i; 
  if(id!=1)  swap(p[id],p[1]); 
  int per[50005];
  for(int i=1;i<=n;i++)  per[i]=i;
  sort(per+2,per+n+1,comp);
  q[++m]=p[1];
  for(int i=2;i<=n;i++)
  {
    int j=per[i];
    while(m>=2&&(q[m]-q[m-1])*(p[j]-q[m-1])<=0)  m--;
    q[++m]=p[j];
  }
  q[++m]=p[1];
}
int area(point u,point v,point s)
{
  return (u-s)*(v-s);
}
int solve()
{
  if(m==2)  return (norm(q[1]-q[2]));
  q[m+1]=q[1];
  int res=0;
  for(int i=1,j=3;i<=m;i++) 
  {
    while(next(j)!=i&&area(q[i],q[i+1],q[j+1])>=area(q[i],q[i+1],q[j]))
      j=next(j);
    res=max(res,norm(q[i+1]-q[j]));
    res=max(res,norm(q[i]-q[j]));
  }
  return res;
}
int main()
{
  //freopen("a.in","r",stdin);
  scanf("%d",&n);
  for(int i=1;i<=n;i++)
    scanf("%d%d",&p[i].x,&p[i].y);
  tubao();
  int ans=solve();
  cout<<ans<<endl;
}