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;
}