230 Kth Smallest Element in a BST

public static int kthSmallest(TreeNode root, int k) {

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

        TreeNode n= root;
        while(n!=null){
            stack.push(n);
            n=n.left;
        }

        while(k>0&&(n!=null||!stack.isEmpty())){

            if(n==null){
                n=stack.pop();
                k--;
                if(k==0)
                    return n.val;
                n=n.right;          
            }else{
                stack.push(n);
                n=n.left;
            }
        }
        return n.val;
    }