From: Mark Hubbart <discordantus@...>
Date: 2005-03-06T02:38:41+09:00
Subject: Re: [QUIZ] Roman Numerals (#22)

On Sat, 5 Mar 2005 00:13:56 +0900, Brian Schr�der <ruby.brian@gmail.com> wrote:
> On Fri, 4 Mar 2005 22:53:20 +0900, Ruby Quiz <james@grayproductions.net> wrote:
> > The three rules of Ruby Quiz:
> >
> > 1.  Please do not post any solutions or spoiler discussion for this quiz until
> > 48 hours have passed from the time on this message.
> >
> > 2.  Support Ruby Quiz by submitting ideas as often as you can:
> >
> > http://www.rubyquiz.com/
> >
> > 3.  Enjoy!
> >
> > -=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
> >
> > This week's quiz is to write a converter to and from Roman numerals.
> >
> > The script should be a standard Unix filter, reading from files specified on the
> > command-line or STDIN and writing to STDOUT.  Each line of input will contain
> > one integer (between 1 and 3999) expressed as an Arabic or Roman numeral.  There
> > should be one line of output for each line of input, containing the original
> > number in the opposite format.
> >
> > For example, given the following input:
> >
> >         III
> >         29
> >         38
> >         CCXCI
> >         1999
> >
> > The correct output is:
> >
> >         3
> >         XXIX
> >         XXXVIII
> >         291
> >         MCMXCIX
> >
> > If you're not familiar with or need a refresher on Roman numerals, the rules are
> > simple.  First, there are seven letters associated with seven values:
> >
> >         I = 1
> >         V = 5
> >         X = 10
> >         L = 50
> >         C = 100
> >         D = 500
> >         M = 1000
> >
> > You can combine letters to add values, by listing them largest to smallest from
> > left to right:
> >
> >         II   is 2
> >         VII  is 8
> >         XXXI is 31
> >
> > However, you may only list three consecutive identical letters.  That requires a
> > special rule to express numbers like 4 and 900.  That rule is that a single
> > lower value may proceed a larger value, to indicate subtraction.  This rule is
> > only used to build values not reachable by the previous rules:
> >
> >         IV is 4
> >         CM is 900
> >
> > But 15 is XV, not XVX.
> >
> >
> 
> Hello James,
> 
> I know that in reality roman numbers didn't always follow the
> conventions given here, so everything is a little bit more complex,
> but this are more or less clear rules. Maybe one should add the
> additional rule that shorter numbers are preferred over longer ones to
> disambiguate a bit more. But the question I'm after:
> 
> When I follow your rules, I calculate MIM for 1999, why do you propose
> the slightly less readable: MCMXCIX for this purpose? Also this does
> not seem to be consistent with XXIX for 29.

The rule of thumb as I remember it is that you can't prefix a symbol
that is greater than one order of magnitude (base ten). So, IX is
okay, where IC and IM are not.

HTH,
Mark