ruby counterstrings

counterstrings.rb

def counter_strings length
    if length.nil?
      return ""
    elsif length == 1
      return '*'
    else
      result = []
      position = 2
      increment = 2
      while  position <= length
        result << "#{position}*"
        if (position + increment)%(10**(increment-1)) < position%(10**(increment-1))
          increment = increment + 1
        end
        position = position + increment
      end
      result_as_string = result.join('')
      if result_as_string.length < length
        return "#{result_as_string}#{position}"
      else
        return result_as_string
      end
    end
end