zoj 1648 判断线段是否相交

  1 #include <stdio.h>
  2 #include <string.h>
  3 #include <stdlib.h>
  4 #include <math.h>
  5 #include <iostream>
  6 #include <algorithm>
  7 #define eps 1e-6
  8 
  9 struct point
 10 {
 11     double x,y;
 12 };
 13 
 14 struct beline
 15 {
 16     point a,b;
 17 };
 18 
 19 using namespace std;
 20 
 21 point p[5000];
 22 
 23 bool dy(double x,double y)
 24 {
 25     return x > y+eps;
 26 }
 27 bool xy(double x,double y)
 28 {
 29     return x < y-eps;
 30 }
 31 bool xyd(double x,double y)
 32 {
 33     return x < y+eps;
 34 }
 35 bool dyd(double x,double y)
 36 {
 37     return x > y-eps;
 38 }
 39 double dd(double x,double y)
 40 {
 41     return fabs(x-y) < eps;
 42 }
 43 
 44 double crossProduct(point a,point b,point c)
 45 {
 46     return (c.x-a.x)*(b.y-a.y)-(c.y-a.y)*(b.x-a.x);
 47 }
 48 
 49 bool onSegment(point a,point b,point c)
 50 {
 51     double maxx=max(a.x,b.x);
 52     double maxy=max(a.y,b.y);
 53     double minx=min(a.x,b.x);
 54     double miny=min(a.y,b.y);
 55     if(dd(crossProduct(a,b,c),0.0)&&dyd(c.x,minx)&&xyd(c.x,maxx)
 56         &&dyd(c.y,miny)&&xyd(c.y,maxy))
 57         return true;
 58     return false;
 59 }
 60 
 61 bool segIntersect(point p1,point p2,point p3,point p4)
 62 {
 63     double d1 = crossProduct(p3,p4,p1);
 64     double d2 = crossProduct(p3,p4,p2);
 65     double d3 = crossProduct(p1,p2,p3);
 66     double d4 = crossProduct(p1,p2,p4);
 67     if(xy(d1*d2,0.0)&&xy(d3*d4,0.0))
 68         return true;
 69     if(dd(d1,0.0)&&onSegment(p3,p4,p1))
 70         return true;
 71     if(dd(d2,0.0)&&onSegment(p3,p4,p2))
 72         return true;
 73     if(dd(d3,0.0)&&onSegment(p1,p2,p3))
 74         return true;
 75     if(dd(d4,0.0)&&onSegment(p1,p2,p4))
 76         return true;
 77     return false;
 78 }
 79 
 80 int main()
 81 {
 82     beline p[5000];
 83     int n,i,j;
 84     while(scanf("%d",&n)!=EOF)
 85     {
 86         for(i=0;i<n;i++)
 87         {
 88                  scanf("%lf%lf%lf%lf",&p[i].a.x,&p[i].a.y,&p[i].b.x,&p[i].b.y);
 89         }
 90 
 91         if(n<=1)
 92         {
 93             printf("ok!\n");
 94             continue;
 95         }
 96 
 97         bool flag=false;
 98         for(i=0;i<n;i++)
 99         {
100             for(j=i+1;j<n;j++)
101             {
102                 if(segIntersect(p[i].a,p[i].b,p[j].a,p[j].b))
103                 {
104                     flag=true;
105                     break;
106                 }
107             }
108         }
109         if(flag)
110         {
111             printf("burned!\n");
112         }
113         else
114         {
115             printf("ok!\n");
116         }
117     }
118     return 0;
119 }