public boolean symmetricalEqual(TreeNode a, TreeNode b){
		if(a == null && b == null)
			return true;
		else if(a != null && b == null || a == null && b != null)
			return false;
		else if(a.val == b.val)
			return true && symmetricalEqual(a.right, b.left) 
					&& symmetricalEqual(a.left, b.right);
		else
			return false;
	}