public boolean recursiveSymmetric(TreeNode left, TreeNode right) {
        if(left == null && right == null) return true;
        if((left == null && right != null) || (left != null && right == null)) return false;
        if(left.val != right.val) return false;
        boolean l = recursiveSymmetric(left.left, right.right);
        boolean r = recursiveSymmetric(left.right, right.left);
        return l && r;
    }