From: William James <w_a_x_man@...>
Date: 2007-01-03T07:30:08+09:00
Subject: Re: Calculating roman numerals

Shiloh Madsen wrote:
> Ok, I'm having trouble with another exercise in this book. It has
> asked me to write a program that will calculate the old school roman
> numeral value for a given modern number (up to the thousands). To
> clarify, old school roman numerals didn't do the subtraction thing, so
> 4 is IIII, nine is VIIII, etc. I've played around with a few options
> using division, loops and modulus, but can't seem to get my brain
> around the problem...any suggestions?
>
> Shiloh
>
> --
> It is better to rule in hell than serve in heaven.

class Integer
  def to_roman
    "I =1       V =5      X = 10       L = 50
    C = 100    D = 500   M = 1000".
    scan( / ([A-Z]) \s *= \s* (\d+) /x ).
    map{|letter,val|  [ letter, val.to_i ] }.
    sort_by{|a| -a.last}.
    inject( [ "", self ] ){|roman, pair|
      [ roman.first + pair.first * (roman.last / pair.last),
        roman.last % pair.last ] }.
    first
  end
end