def node_to_row node
      crow = nil
      @list.each_with_index { |e,i| 
        if e == node
          crow = i
          break
        end
      }
      crow
    end
def node_to_row node
      crow = nil
      @list.each_with_index { |e,i| 
        if e == node
          crow = i
          break
        end
      }
      crow
    end
convert a given node to row