diff options
Diffstat (limited to 'Algorithms/Part-I/5-KdTrees')
| -rw-r--r-- | Algorithms/Part-I/5-KdTrees/KdTree.java | 207 |
1 files changed, 202 insertions, 5 deletions
diff --git a/Algorithms/Part-I/5-KdTrees/KdTree.java b/Algorithms/Part-I/5-KdTrees/KdTree.java index 877a2c3..73d9a90 100644 --- a/Algorithms/Part-I/5-KdTrees/KdTree.java +++ b/Algorithms/Part-I/5-KdTrees/KdTree.java @@ -2,49 +2,246 @@ public class KdTree { + private static final double XMIN = 0; + private static final double YMIN = 0; + private static final double XMAX = 1; + private static final double YMAX = 1; + + private Node root; + private int size; + + private class Node { + private Point2D p; + private Node left, right; + + public Node(Point2D p) + { + this.p = p; + } + } + + private class NearestChampion { + private Point2D p; + private double d; + public NearestChampion(Point2D p, double d) + { + this.p = p; + this.d = d; + } + } + // construct an empty tree of points public KdTree() { + size = 0; + root = null; } // is the tree empty? public boolean isEmpty() { - return true; + return (size == 0); } // number of points in the tree public int size() { - return 0; + return size; } // add the point p to the tree (if it is not already in the tree) public void insert(Point2D p) { + if (p == null) return; + if (root == null) + { + root = new Node(p); + size = 1; + } + else if (put(root, p, true)) + size += 1; + } + + private boolean put(Node n, Point2D p, boolean vsplit) { + + int cmp; + if (vsplit) + cmp = Point2D.X_ORDER.compare(p, n.p); + else + cmp = Point2D.Y_ORDER.compare(p, n.p); + + if (cmp < 0) + { + // add to left subtree + if (n.left != null) + return put(n.left, p, !vsplit); + n.left = new Node(p); + return true; + } + + if (cmp == 0) + { + if (vsplit) + { + if (Point2D.Y_ORDER.compare(p, n.p) == 0) + return false; + } + else if (Point2D.X_ORDER.compare(p, n.p) == 0) + return false; + } + + // add to right subtree + if (n.right != null) + return put(n.right, p, !vsplit); + n.right = new Node(p); + return true; } // does the tree contain the point p? public boolean contains(Point2D p) { - return false; + if (root == null) return false; + return get(root, p, true); + } + + private boolean get(Node n, Point2D p, boolean vsplit) { + if (p.compareTo(n.p) == 0) return true; + int cmp; + if (vsplit) + cmp = Point2D.X_ORDER.compare(p, n.p); + else + cmp = Point2D.Y_ORDER.compare(p, n.p); + + if (cmp < 0) + return get(n.left, p, !vsplit); + return get(n.right, p, !vsplit); } // draw all of the points to standard draw public void draw() { + StdDraw.setPenRadius(); + StdDraw.setPenColor(StdDraw.BLACK); + StdDraw.rectangle(XMAX/2.0, YMAX/2.0, XMAX/2.0, YMAX/2.0); + draw(root, true, new RectHV(XMIN, YMIN, XMAX, YMAX)); + } + + private void draw(Node n, boolean vsplit, RectHV r) + { + if (n == null) return; + if (vsplit) + { + StdDraw.setPenRadius(); + StdDraw.setPenColor(StdDraw.RED); + StdDraw.line(n.p.x(), r.ymin(), n.p.x(), r.ymax()); + if (n.left != null) + draw(n.left, !vsplit, + new RectHV(r.xmin(), r.ymin(), n.p.x(), r.ymax())); + if (n.right != null) + draw(n.right, !vsplit, + new RectHV(n.p.x(), r.ymin(), r.xmax(), r.ymax())); + } + else + { + StdDraw.setPenRadius(); + StdDraw.setPenColor(StdDraw.BLUE); + StdDraw.line(r.xmin(), n.p.y(), r.xmax(), n.p.y()); + if (n.left != null) + draw(n.left, !vsplit, + new RectHV(r.xmin(), r.ymin(), r.xmax(), n.p.y())); + if (n.right != null) + draw(n.right, !vsplit, + new RectHV(r.xmin(), n.p.y(), r.xmax(), r.ymax())); + } + StdDraw.setPenRadius(.01); + StdDraw.setPenColor(StdDraw.BLACK); + n.p.draw(); } // all points in the tree that are inside the rectangle public Iterable<Point2D> range(RectHV rect) { - return null; + Stack<Point2D> stack = new Stack<Point2D>(); + + range(root, rect, stack, true); + + return stack; + } + + private void range(Node n, RectHV r, Stack<Point2D> s, boolean vsplit) + { + if (r.contains(n.p)) + s.push(n.p); + if (vsplit) + { + if (n.left != null && r.xmin() < n.p.x()) + range(n.left, r, s, !vsplit); + if (n.right != null && r.xmax() >= n.p.x()) + range(n.right, r, s, !vsplit); + } + else + { + if (n.left != null && r.ymin() < n.p.y()) + range(n.left, r, s, !vsplit); + if (n.right != null && r.ymax() >= n.p.y()) + range(n.right, r, s, !vsplit); + } } // a nearest neighbor in the tree to p; null if tree is empty public Point2D nearest(Point2D p) { - return null; + if (p == null) return null; + if (root == null) return null; + NearestChampion ncp = new NearestChampion(null, Double.MAX_VALUE); + nearest(root, p, ncp, true); + return ncp.p; + } + + private void nearest(Node n, Point2D p, NearestChampion ncp, boolean vsplit) + { + double d2 = p.distanceTo(n.p); + if (d2 < ncp.d) + { + ncp.d = d2; + ncp.p = n.p; + } + if (vsplit) + { + double nx = n.p.x(); + if (p.x() < nx) + { + if (n.left != null) + nearest(n.left, p, ncp, !vsplit); + if (n.right != null && ((nx - p.x()) < ncp.d)) + nearest(n.right, p, ncp, !vsplit); + } + else + { + if (n.right != null) + nearest(n.right, p, ncp, !vsplit); + if (n.left != null && ((p.x() - nx) < ncp.d)) + nearest(n.left, p, ncp, !vsplit); + } + } + else + { + double ny = n.p.y(); + if (p.y() < ny) + { + if (n.left != null) + nearest(n.left, p, ncp, !vsplit); + if (n.right != null && ((ny - p.y()) < ncp.d)) + nearest(n.right, p, ncp, !vsplit); + } + else + { + if (n.right != null) + nearest(n.right, p, ncp, !vsplit); + if (n.left != null && ((p.y() - ny) < ncp.d)) + nearest(n.left, p, ncp, !vsplit); + } + } } } |