poj 1410 Intersection

  1 #include <cstdio>
  2 #include<algorithm>
  3 #include<iostream>
  4 #include<string>
  5 #include<cstring>
  6 #include<vector>
  7 using namespace std;
  8 struct point{
  9     double x,y;
 10 };
 11 double det(point a,point b,point c){
 12     return (b.x-a.x)*(c.y-a.y)-(c.x-a.x)*(b.y-a.y);
 13 }
 14 point a,b,c,d,e,f;
 15 bool check(point e){
 16     if(e.x>=a.x&&e.y<=a.y&&e.x<=c.x&&e.y>=c.y){
 17         return true;
 18     }
 19     return false;
 20 }
 21 double max(double a,double b){
 22     if(a>b){
 23         return a;
 24     }
 25     return b;
 26 }
 27 double min(double a,double b){
 28     if(a>b){
 29         return b;
 30     }
 31     return a;
 32 }
 33 int main(){
 34     int n;
 35     cin>>n;
 36     while(n--){
 37         double xl,yt,xr,yb;
 38         cin>>e.x>>e.y>>f.x>>f.y>>xl>>yt>>xr>>yb;
 39         if(xl>xr){
 40             double x=xl;
 41             xl=xr;    
 42             xr=x;
 43         }
 44         if(yt<yb){
 45             double y=yt;    
 46             yt=yb;
 47             yb=y;
 48         }
 49         a.x=xl;
 50         a.y=yt;
 51         b.x=xr;
 52         b.y=yt;
 53         c.x=xr;
 54         c.y=yb;
 55         d.x=xl;
 56         d.y=yb;
 57         if(check(e)||check(f)){//线段有至少一个端点在矩形内部或边界上
 58             cout<<"T"<<endl;
 59             continue;
 60         }
 61         double aa,bb,cc,dd;
 62         aa=det(e,a,b)*det(f,a,b),bb=det(a,e,f)*det(b,e,f);
 63         if(aa==0&&bb==0&&(max(e.x,f.x)<min(b.x,a.x)||max(e.y,f.y)<min(b.y,a.y)||max(b.x,a.x)<min(e.x,f.x)||max(b.y,a.y)<min(e.y,f.y))){//特殊情况：线段与矩形四条边界中的任一条共线，但满足次条件表示没有公共交点
 64             cout<<"F"<<endl;
 65             continue;
 66         }
 67         if(aa<=0&&bb<=0){//除去前面的特殊情况，满足次条件表示两线段相交
 68             cout<<"T"<<endl;
 69             continue;
 70         }
 71         /*if(det(e,b,c)*det(f,b,c)<=0&&det(b,e,f)*det(c,e,f)<=0){
 72             cout<<"det(e,b,c): "<<det(e,b,c)<<endl;
 73             cout<<"det(f,b,c): "<<det(f,b,c)<<endl;
 74             cout<<"det(b,e,f): "<<det(b,e,f)<<endl;
 75             cout<<"det(c,e,f): "<<det(c,e,f)<<endl;
 76             cout<<"T"<<endl;
 77             continue;
 78         }*/
 79         aa=det(e,b,c)*det(f,b,c),bb=det(b,e,f)*det(c,e,f);
 80         if(aa==0&&bb==0&&(max(e.x,f.x)<min(b.x,c.x)||max(e.y,f.y)<min(b.y,c.y)||max(b.x,c.x)<min(e.x,f.x)||max(b.y,c.y)<min(e.y,f.y))){
 81             cout<<"F"<<endl;
 82             continue;
 83         }
 84         if(aa<=0&&bb<=0){
 85             cout<<"T"<<endl;
 86             continue;
 87         }
 88         
 89         aa=det(e,c,d)*det(f,c,d),bb=det(c,e,f)*det(d,e,f);
 90         if(aa==0&&bb==0&&(max(e.x,f.x)<min(c.x,d.x)||max(e.y,f.y)<min(c.y,d.y)||max(c.x,d.x)<min(e.x,f.x)||max(c.y,d.y)<min(e.y,f.y))){
 91             cout<<"F"<<endl;
 92             continue;
 93         }
 94         if(aa<=0&&bb<=0){
 95             cout<<"T"<<endl;
 96             continue;
 97         }
 98         
 99         aa=det(e,d,a)*det(f,d,a),bb=det(d,e,f)*det(a,e,f);
100         if(aa==0&&bb==0&&(max(e.x,f.x)<min(a.x,d.x)||max(e.y,f.y)<min(a.y,d.y)||max(a.x,d.x)<min(e.x,f.x)||max(a.y,d.y)<min(e.y,f.y))){
101             cout<<"F"<<endl;
102             continue;
103         }
104         if(aa<=0&&bb<=0){
105             cout<<"T"<<endl;
106             continue;
107         }
108         
109         cout<<"F"<<endl;
110     }
111     return 0;
112 }