public boolean isValidBST_II(TreeNode root) {
        if (root == null)
            return true;
        getInorder(root);
        for (int i = 0; i < arrs.size() - 1; ++i) {
            if (arrs.get(i) < arrs.get(i + 1)) {
                continue;
            } else
                return false;
        }
        return true;
    }