leetcode230. kth smallest element in a bst

public int count = 0;
public int ans = 0;
public int (TreeNode root, int k) {
    count = k;
    if (root != null) inorderWalk(root);
    return ans;
}
public void inorderWalk(TreeNode root) {
    if (root == null) return;
    inorderWalk(root.left);
    count--;
    if (count == 0) {
        ans = root.val;
        return;
    }
    inorderWalk(root.right);
}