/**
 * Definition for a binary tree node.
 * public class TreeNode {
 * int val;
 * TreeNode left;
 * TreeNode right;
 * TreeNode(int x) { val = x; }
 * }
 */
class BSTIterator {
 
 private TreeNode currentNode = null;
 private Stack<TreeNode> stack = new Stack<TreeNode>();
 public BSTIterator(TreeNode root) {
 if (root != null) {
 currentNode = root;
 }
 }
 
 /** @return the next smallest number */
 public int next() {
 while (currentNode != null) {
 stack.push(currentNode);
 currentNode = currentNode.left;
 }
 currentNode = stack.pop();
 TreeNode node = currentNode;
 currentNode = currentNode.right;
 return node.val;
 }
 
 /** @return whether we have a next smallest number */
 public boolean hasNext() {
 return currentNode != null || !stack.isEmpty();
 }
}
/**
 * Your BSTIterator object will be instantiated and called as such:
 * BSTIterator obj = new BSTIterator(root);
 * int param_1 = obj.next();
 * boolean param_2 = obj.hasNext();
 */