线段相交 POJ 2653

// 线段相交 POJ 2653
// 思路：数据比较水，据说n^2也可以过
// 我是每次枚举线段，和最上面的线段比较
// O(n*m)

// #include <bits/stdc++.h>
#include <iostream>
#include <cstdio>
#include <cstdlib>
#include <algorithm>
#include <vector>
#include <math.h>
using namespace std;
#define LL long long
typedef pair<int,int> pii;
const double inf = 123456789012345.0;
const LL MOD =100000000LL;
const int N =1e5+10;
#define clc(a,b) memset(a,b,sizeof(a))
const double eps = 1e-8;
void fre() {freopen("in.txt","r",stdin);}
void freout() {freopen("out.txt","w",stdout);}
inline int read() {int x=0,f=1;char ch=getchar();while(ch>'9'||ch<'0') {if(ch=='-') f=-1; ch=getchar();}while(ch>='0'&&ch<='9') {x=x*10+ch-'0';ch=getchar();}return x*f;}

int sgn(double x){
    if(fabs(x) < eps)return 0;
    if(x < 0)return -1;
    else return 1;
}
struct Point{
    double x,y;
    Point(){}
    Point(double _x,double _y){
        x = _x;y = _y;
    }
    Point operator -(const Point &b)const{
        return Point(x - b.x,y - b.y);
    }
    double operator ^(const Point &b)const{
        return x*b.y - y*b.x;
    }
    double operator *(const Point &b)const{
        return x*b.x + y*b.y;
    }
};

struct Line{
    Point s,e;
    int inx;
    Line(){}
    Line(Point _s,Point _e){
        s=_s;e=_e;
    }
    // pair<int,Point> operator & (const Line &b) const{
    //     Point res=s;
    //     if(sgn((s-e)^(b.s-b.e))==0){
    //         if(sgn((s-b.e)^(b.s-b.e))==0) 
    //             return make_pair(0,res);
    //         else  return make_pair(1,res);
    //     }
    //     double t=((s-b.s)^(b.s-b.e))/((s-e)^(b.s-b.e));
    //     res.x+=(e.x-s.x)*t;
    //     res.y+=(e.y-s.y)*t;
    //     return make_pair(2,res);
    // }
};

Line line[N];
bool inter(Line l1,Line l2){
    return 
        max(l1.s.x,l1.e.x) >= min(l2.s.x,l2.e.x) &&
        max(l2.s.x,l2.e.x) >= min(l1.s.x,l1.e.x) &&
        max(l1.s.y,l1.e.y) >= min(l2.s.y,l2.e.y) &&
        max(l2.s.y,l2.e.y) >= min(l1.s.y,l1.e.y) &&
        sgn((l2.s-l1.s)^(l1.e-l1.s))*sgn((l2.e-l1.s)^(l1.e-l1.s)) <= 0 &&
        sgn((l1.s-l2.s)^(l2.e-l2.s))*sgn((l1.e-l2.s)^(l2.e-l2.s)) <= 0;
}

vector<Line> list;
bool cmp(Line l1,Line l2){
    return l1.inx<l2.inx;
}

int main(){
    vector<Line>::iterator it;
    int n;
    while(~scanf("%d",&n),n){
        list.clear();
        for(int i=1;i<=n;i++){
           double x1,x2,y2,y1;
        scanf("%lf%lf%lf%lf",&x1,&y1,&x2,&y2);
        line[i]=Line(Point(x1,y1),Point(x2,y2));
        line[i].inx=i;
    }
    list.push_back(line[1]);
    for(int i=2;i<=n;i++){
        for(it=list.begin();it!=list.end();){
           if(inter(line[i],*it)){
              it=list.erase(it);
           }
           else it++;
        }
        list.push_back(line[i]);
    }
    printf("Top sticks: ");
    sort(line+1,line+1+list.size(),cmp);
    for(it=list.begin();it!=list.end();it++){
        if(it!=list.end()-1){
            printf("%d, ",(*it).inx);
        }
        else printf("%d.\n",(*it).inx);
    }
    }
    return 0;
}