判断两条线段是否相交的方法

 1 struct pos
 2 {
 3      double x ;
 4      double y ;
 5 };
 6 struct line
 7 {
 8      pos st ;
 9      pos end ;
10 };
11 int n ;
12 
13     
14 double Multiply(pos p1, pos p2, pos p0)  
15 {  
16      return ( (p1.x - p0.x) * (p2.y - p0.y) - (p2.x - p0.x) * (p1.y - p0.y) );  
17 }   
18     
19 bool iscross(line L1, line L2)  
20 {  
21      return( (max(L1.st.x,   L1.end.x) >= min(L2.st.x, L2.end.x)) &&  
22          (max(L2.st.x,   L2.end.x) >= min(L1.st.x, L1.end.x)) &&  
23          (max(L1.st.y,   L1.end.y) >= min(L2.st.y, L2.end.y)) &&  
24          (max(L2.st.y,   L2.end.y) >= min(L1.st.y, L1.end.y)) &&  
25          (Multiply(L2.st, L1.end, L1.st) * Multiply(L1.end, L2.end, L1.st) >= 0) &&  
26          (Multiply(L1.st, L2.end, L2.st) * Multiply(L2.end, L1.end, L2.st) >= 0)  
27          );  
28 }
29 
30