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Ingy döt Net 2023-07-01 11:58:00 -04:00
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34
Task/Convex-hull/Scala/convex-hull.scala Normal file
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object convex_hull{
def get_hull(points:List[(Double,Double)], hull:List[(Double,Double)]):List[(Double,Double)] = points match{
case Nil => join_tail(hull,hull.size -1)
case head :: tail => get_hull(tail,reduce(head::hull))
}
def reduce(hull:List[(Double,Double)]):List[(Double,Double)] = hull match{
case p1::p2::p3::rest => {
if(check_point(p1,p2,p3)) hull
else reduce(p1::p3::rest)
}
case _ => hull
}
def check_point(pnt:(Double,Double), p2:(Double,Double),p1:(Double,Double)): Boolean = {
val (x,y) = (pnt._1,pnt._2)
val (x1,y1) = (p1._1,p1._2)
val (x2,y2) = (p2._1,p2._2)
((x-x1)*(y2-y1) - (x2-x1)*(y-y1)) <= 0
}
def m(p1:(Double,Double), p2:(Double,Double)):Double = {
if(p2._1 == p1._1 && p1._2>p2._2) 90
else if(p2._1 == p1._1 && p1._2<p2._2) -90
else if(p1._1<p2._1) 180 - Math.toDegrees(Math.atan(-(p1._2 - p2._2)/(p1._1 - p2._1)))
else Math.toDegrees(Math.atan((p1._2 - p2._2)/(p1._1 - p2._1)))
}
def join_tail(hull:List[(Double,Double)],len:Int):List[(Double,Double)] = {
if(m(hull(len),hull(0)) > m(hull(len-1),hull(0))) join_tail(hull.slice(0,len),len-1)
else hull
}
def main(args:Array[String]){
val points = List[(Double,Double)]((16,3), (12,17), (0,6), (-4,-6), (16,6), (16,-7), (16,-3), (17,-4), (5,19), (19,-8), (3,16), (12,13), (3,-4), (17,5), (-3,15), (-3,-9), (0,11), (-9,-3), (-4,-2), (12,10))
val sorted_points = points.sortWith(m(_,(0.0,0.0)) < m(_,(0.0,0.0)))
println(f"Points:\n" + points + f"\n\nConvex Hull :\n" +get_hull(sorted_points,List[(Double,Double)]()))
}
}