java - Constructing a 3D KD Tree -


so trying construct 3d kd tree list of randomly generated points. trying accomplish task recursively well. in recursion facing error when i'm trying partition list of points. code follows:

public class scratch {      /**      * @param args command line arguments      */     public static void main(string[] args) {         arraylist<point> points = new arraylist<point>();         random rand = new random(system.currenttimemillis());         (int = 0; < 100; i++) {             double x = rand.nextint(100);             double y = rand.nextint(100);             double z = rand.nextint(100);             point point = new point(x, y, z);             points.add(point);         }         node root = kdtree(points, 0);         system.out.println("done");     }      static class node {          node leftchild;         node rightchild;         point location;          node() {          }          node(node leftchild, node rightchild, point location) {             this.leftchild = leftchild;             this.rightchild = rightchild;             this.location = location;         }     }      public static node kdtree(arraylist<point> points, int depth) {         int axis = depth % 3;         switch (axis) {             case 0:                 collections.sort(points, point.x_comparator);                 break;             case 1:                 collections.sort(points, point.y_comparator);                 break;             case 2:                 collections.sort(points, point.z_comparator);                 break;             default:                 break;         }         int middle = points.size() / 2;         point median = points.get(middle);          arraylist<point> greater = new arraylist<point>(points.sublist(0, (middle - 1)));         arraylist<point> lesser = new arraylist<point>(points.sublist((middle + 1), (points.size())));         node node = new node();         node.location = median;         if(greater.size() == 0 || lesser.size() == 0) {             node.leftchild = null;             node.rightchild = null;         } else {             node.leftchild = kdtree(lesser, depth + 1);             node.rightchild = kdtree(greater, depth + 1);         }                 return node;     }  }

the class point simple object contains x, y , z coordinate. , 3 comparators used based on depth of tree. error getting follows: 

exception in thread "main" java.lang.illegalargumentexception: fromindex(0) > toindex(-1)     @ java.util.arraylist.sublistrangecheck(arraylist.java:1006)     @ java.util.arraylist.sublist(arraylist.java:996)     @ scratch.scratch.kdtree(scratch.java:71)     @ scratch.scratch.kdtree(scratch.java:80)     @ scratch.scratch.kdtree(scratch.java:79)     @ scratch.scratch.kdtree(scratch.java:79)     @ scratch.scratch.kdtree(scratch.java:79)     @ scratch.scratch.kdtree(scratch.java:79)     @ scratch.scratch.main(scratch.java:32)

im gonna go on guess here , if have 1 point (or 0) on points array, when middle=points.size/2 equals 0 (integer division) , when try make sublist 0 -1 throws exception.


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