class IntervalSkipList

def containing_with_node(n)
  containing = []
  cur_node = head
  (max_height - 1).downto(0) do |cur_level|
    while (next_node = cur_node.forward[cur_level]) && next_node.key <= n
      cur_node = next_node
      if cur_node.key == n
        return containing + (cur_node.markers - cur_node.endpoint_of), cur_node
      end
    end
    containing.concat(cur_node.forward_markers[cur_level])
  end
  return containing, cur_node
end