270. Closest Binary Search Tree Value

        /*
     * 270. Closest Binary Search Tree Value
     * 2016-6-25 by Mingyang
     */
      public int closestValue(TreeNode root, double target) {
            int closest = root.val;
            double min = Double.MAX_VALUE;
            while(root!=null) {
                if( Math.abs(root.val - target) < min  ) {
                    min = Math.abs(root.val - target);
                    closest = root.val;
                }
                if(target < root.val) {
                    root = root.left;
                } else if(target > root.val) {
                    root = root.right;
                } else {
                    return root.val;
                }
            }
            return closest;
        }