Roman numeral conversion sample code

gistfile1.rb

class Roman
  Memo = {}
  Code = [["","I","II","III","IV","V","VI","VII","VIII","IX"],
          ["","X","XX","XXX","XL","L","LX","LXX","LXXX","XC"],
          ["","C","CC","CCC","CD","D","DC","DCC","DCCC","CM"],
          ["","M","MM","MMM"]]

  def self.to_roman(n)
    Memo[n] ||= begin
      l = Math.log10(n).to_i
      q,r = n.divmod(10**l)
      Code[l][q] + (r > 0 ? to_roman(r) : "")
    end
  end

end