HDU1086+几何+判断线段相交

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 1 /*

 2 几何+线段相交

 3 */

 4 #include<stdio.h>

 5 #include<string.h>

 6 #include<stdlib.h>

 7 #include<algorithm>

 8 #include<iostream>

 9 #include<queue>

10 //#include<map>

11 #include<math.h>

12 using namespace std;

13 typedef long long ll;

14 //typedef __int64 int64;

15 const int maxn = 105;

16 const int inf = 0x7fffffff;

17 const double pi=acos(-1.0);

18 const double eps = 1e-8;

19 struct point {

20     double x,y;

21 };

22 struct line{

23     point a,b;

24 };

25 line myline[ maxn ];

26 

27 double xmult( point a,point b,point c ){

28     return ( a.x-c.x )*( b.y-c.y )-( a.y-c.y )*( b.x-c.x );

29 }

30 bool inLine( line now,point p ){

31     double minx,maxx,miny,maxy;

32     minx=min( now.a.x,now.b.x );

33     maxx=max( now.a.x,now.b.x );

34     miny=min( now.a.y,now.b.y );

35     maxy=max( now.a.y,now.b.y );

36     if( p.x>=minx&&p.x<=maxx&&p.y>=miny&&p.y<=maxy )

37         return true;

38     else

39         return false;

40 }

41 bool intersect( line one,line two ){

42     double d1,d2,d3,d4;

43     d1=xmult( two.a,one.b,one.a );

44     d2=xmult( two.b,one.b,one.a );

45     d3=xmult( one.a,two.a,two.b );

46     d4=xmult( one.b,two.a,two.b );

47     if( d1*d2<0&&d3*d4<0 )

48         return true;//相互跨过

49     if( d1==0&&inLine( one,two.a )==true )

50         return true;

51     if( d2==0&&inLine( one,two.b )==true )

52         return true;

53     if( d3==0&&inLine( two,one.a )==true )

54         return true;

55     if( d4==0&&inLine( two,one.b )==true )

56         return true;//分别表示某个点在一条直线上的情况

57     return false;

58 }

59 

60 int main(){

61     int n;

62     while( scanf("%d",&n)!=EOF,n ){

63         for( int i=0;i<n;i++ ){

64             scanf("%lf%lf%lf%lf",&myline[ i ].a.x,&myline[ i ].a.y,&myline[ i ].b.x,&myline[ i ].b.y);

65         }

66         int sum=0;//交点的个数

67         for( int i=0;i<n;i++ ){

68             for( int j=i+1;j<n;j++ ){

69                 if( intersect( myline[ i ],myline[ j ] )==true )

70                     sum++;

71             }

72         }

73         printf("%d\n",sum);

74     }

75     return 0;

76 }