二叉搜索树的第k个结点

    TreeNode KthNode(TreeNode pRoot, int k) {

        if(count > k || pRoot == null)

            return null;

        TreeNode p = pRoot;

        Stack<TreeNode> stack = new Stack<>();

        TreeNode kthNode = null;

        stack.push(pRoot);

        while(!stack.isEmpty()){

            TreeNode tn = stack.peek();

            while(tn != null){

                tn = tn.left;

                stack.push(tn);

            }

            stack.pop();

            if (!stack.isEmpty()) {

                tn = stack.pop();

                count++;

                if (count == k)

                    kthNode = tn;

                stack.push(tn.right);

            }

        }

        return kthNode; 

    }