Method nearest

05Lab-Kd Tree/KdTree.java:128–134

(Point2D p)

    // a nearest neighbor in the set to point p; null if the set is empty
    public Point2D nearest(Point2D p) {
        if (p == null) throw new IllegalArgumentException();
        if (isEmpty()) return null;
        Champion champion = new Champion(root.p, Double.POSITIVE_INFINITY);
        nearest(p, root, true, champion);
        return champion.p;
    }

    private void nearest(Point2D p, Node nd, boolean flag, Champion champion) {
        double queryD = p.distanceSquaredTo(nd.p);