From: William James <w_a_x_man@...>
Date: 2006-12-10T01:50:06+09:00
Subject: Re: Need help on a program

Christopher Latif wrote:
> Stuck on this exercise from a book:
> Old-school Roman numerals. In the early days of Roman numerals,
> the Romans didn't bother with any of this new-fangled subtraction
> "IX" nonsense. No sir, it was straight addition, biggest to littlest-
> so 9 was written "VIIII," and so on. Write a method that, when
> passed an integer between 1 and 3000 (or so), returns a string
> containing the proper old-school Roman numeral. In other words,
> old_roman_numeral 4 should return 'IIII'. Make sure to test
> your method on a bunch of different numbers.
> For reference, these are the values of the letters used:
> I =1       V =5      X = 10       L = 50
> C = 100    D = 500   M = 1000
>
> Suggestions on a soloution?
>
> --
> Posted via http://www.ruby-forum.com/.

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