From: William James <w_a_x_man@...>
Date: 2007-01-04T21:35:09+09:00
Subject: Re: Calculating roman numerals

Gregory Seidman wrote:
> 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

Another way:

require 'enumerator'
def y s
  t=0
  (s.split("").map{|c|
    n=' IVXLCDM'.index c;10**(n/2)/(2-n%2)}<<0).
  each_cons(2){|a,b| t+= a<b ?-a:a}
  t
end