From: Gregory Seidman <gsslist+ruby@...>
Date: 2007-01-03T21:45:43+09:00
Subject: Re: Calculating roman numerals

On Wed, Jan 03, 2007 at 06:35:02AM +0900, 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?

We recently had a golfing competition at work on going the other direction
(i.e. roman numeral to arabic). Our best solution:

def x s
  p=t=0
  s.scan(/./){|r|
    i=' IVXLCDM'.index r
      c=10**(i/2)/(2-i%2)
      t+= p<c ?-p:p
      p=c
  }
  t+p
end

} Shiloh
--Greg