check whether the distinct line segments intersect
bool doIntersect ( Point p1 , Point q1 , Point p2 , Point q2 ) { int o1 = orientation ( p1 , q1 , p2 ) ; int o2 = orientation ( p1 , q1 , q2 ) ; int o3 = orientation ( p2 , q2 , p1 ) ; int o4 = orientation ( p2 , q2 , q1 ) ; if ( o1 != o2 && o3 != o4 ) return true ; return false ; }