poj 2653 Pick-up sticks 计算几何

/*********************************************************************
FileName: 2653.cpp
Author: kojimai
Created Time: 2014年08月08日 星期五 20时16分54秒
*********************************************************************/
#include<vector>
#include<iostream>
#include<cstdio>
#include<cmath>
#include<cstring>
#include<algorithm>
using namespace std;
#define FFF 100005
struct node
{
double x1,y1,x2,y2;
}p[FFF];
const double eps=1e-8;
vector<int> s;
double xmult(double x1,double y1,double x2,double y2,double x3,double y3)
{
return (x1-x3)*(y2-y3)-(y1-y3)*(x2-x3);
}
double dots_inline(double x1,double y1,double x2,double y2,double x3,double y3)
{
if(fabs(xmult(x1,y1,x2,y2,x3,y3))<eps)
return true;
else
return false;
}
bool dot_online(double x1,double y1,double x2,double y2,double x3,double y3)
{
return fabs(xmult(x1,y1,x2,y2,x3,y3))<eps&&(x2-x1)*(x3-x1)<eps&&(y2-y1)*(y3-y1)<eps;
}
bool same_side(double x1,double y1,double x2,double y2,double x3,double y3,double x4,double y4)
{
return xmult(x3,y3,x1,y1,x4,y4)*xmult(x3,y3,x2,y2,x4,y4)>eps;
}
bool judge(int x,int y)
{
if(!dots_inline(p[x].x1,p[x].y1,p[x].x2,p[x].y2,p[y].x1,p[y].y1)||!dots_inline(p[x].x1,p[x].y1,p[x].x2,p[x].y2,p[y].x2,p[y].y2))
return !same_side(p[x].x1,p[x].y1,p[x].x2,p[x].y2,p[y].x1,p[y].y1,p[y].x2,p[y].y2)&&!same_side(p[y].x1,p[y].y1,p[y].x2,p[y].y2,p[x].x1,p[x].y1,p[x].x2,p[x].y2);
return dot_online(p[x].x1,p[x].y1,p[y].x1,p[y].y1,p[y].x2,p[y].y2)||dot_online(p[x].x2,p[x].y2,p[y].x1,p[y].y1,p[y].x2,p[y].y2)||dot_online(p[y].x1,p[y].y1,p[x].x1,p[x].y1,p[x].x2,p[x].y2)||dot_online(p[y].x2,p[y].y2,p[x].x1,p[x].y1,p[x].x2,p[x].y2);
}
int main()
{
int n;
while(scanf("%d",&n),n)
{
s.clear();
for(int i=1;i<=n;i++)
{
scanf("%lf%lf%lf%lf",&p[i].x1,&p[i].y1,&p[i].x2,&p[i].y2);
for(int j=0;j<s.size();)
{
if(judge(s[j],i))
s.erase(s.begin()+j);
else
j++;
}
s.push_back(i);
}
printf("Top sticks:");
for(int i=0;i<s.size()-1;i++)
{
printf(" %d,",s[i]);
}
printf(" %d.\n",s[s.size()-1]);
}
return 0;
}