Java for LeetCode 230 Kth Smallest Element in a BST

int res = 0;
	int k = 0;

	public int kthSmallest(TreeNode root, int k) {
		this.k = k;
		inorderTraversal(root);
		return res;
	}

	public List<Integer> inorderTraversal(TreeNode root) {
		List<Integer> list = new ArrayList<Integer>();
		if (root == null)
			return list;
		if (root.left != null && list.size() < k)
			list.addAll(inorderTraversal(root.left));
		list.add(root.val);
		if (root.right != null && list.size() < k)
			list.addAll(inorderTraversal(root.right));
		if(list.size()==k){
			res=list.get(k-1);
			return list;
		}
		return list;
	}