线段相交 poj 1066

 // 线段相交 poj 1066
 // 思路：直接枚举每个端点和终点连成线段，判断和剩下的线段相交个数

 // #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 int inf = 0x3f3f3f3f;
 const LL MOD =100000000LL;
 const int N =;
 #define clc(a,b) memset(a,b,sizeof(a))
 const double eps = 1e-;
 void fre() {freopen("in.txt","r",stdin);}
 void freout() {freopen("out.txt","w",stdout);}
 inline int read() {int x=,f=;char ch=getchar();while(ch>''||ch<'') {if(ch=='-') f=-; ch=getchar();}while(ch>=''&&ch<='') {x=x*+ch-'';ch=getchar();}return x*f;}

 int sgn(double x){
     if(fabs(x) < eps)return ;
     if(x < )return -;
     else return ;
 }
 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;
     }
 };

 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)) <=  &&
         sgn((l1.s-l2.s)^(l2.e-l2.s))*sgn((l1.e-l2.s)^(l2.e-l2.s)) <= ;
 }

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

 Point p[];
 int main(){
     int n;
     while(~scanf("%d",&n)){
     for(int i=;i<=n;i++){
         double x1,y1,x2,y2;
         scanf("%lf%lf%lf%lf",&x1,&y1,&x2,&y2);
         line[i]=Line(Point(x1,y1),Point(x2,y2));
         p[i*-]=Point(x1,y1);
         p[i*]=Point(x2,y2);
     }
     double x1,y1;
     scanf("%lf%lf",&x1,&y1);
     Point s=Point(x1,y1);
     int ans=inf;
     for(int i=;i<=*n;i++){
        int tem=;
        for(int j=;j<=n;j++){
           if(inter(Line(s,p[i]),line[j]))
             tem++;
        }
        ans=min(ans,tem);
     }

     Point p1;
     p1=Point(,);
     int tem=;
     for(int i=;i<=n;i++){
         if(inter(Line(s,p1),line[i]))
           tem++;
     }
     ans=min(ans,tem+);

     p1=Point(,);
     tem=;
     for(int i=;i<=n;i++){
         if(inter(Line(s,p1),line[i]))
           tem++;
     }
     ans=min(ans,tem+);

     p1=Point(,);
      tem=;
     for(int i=;i<=n;i++){
         if(inter(Line(s,p1),line[i]))
           tem++;
     }
     ans=min(ans,tem+);

     p1=Point(,);
     tem=;
     for(int i=;i<=n;i++){
         if(inter(Line(s,p1),line[i]))
           tem++;
     }
     ans=min(ans,tem+);
     printf("Number of doors = ");
     printf("%d\n",ans);
     }
     return ;
 }