From: Jan Svitok <jan.svitok@...>
Date: 2006-12-09T22:04:50+09:00
Subject: Re: Need help on a program

On 12/9/06, Christopher Latif <christopherl@bredband.net> 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?

1. skeleton (I'll use test/unit, as it's easier to check the results)

require 'test/unit'

def to_roman(int)
   # here comes the code
end

class TestToRoman < Test::Unit::TestCase
   # check the base digits
   def test_roman_digits
       assert_equal 'I', to_roman(1)
       assert_equal 'V', to_roman(5)
       assert_equal 'X', to_roman(10)
       assert_equal 'L', to_roman(50)
       assert_equal 'C', to_roman(100)
       assert_equal 'D', to_roman(500)
       assert_equal 'M', to_roman(1000)
   end

   def test_roman_more
       assert_equal 'I', to_roman(1)
       assert_equal 'II', to_roman(2)
       assert_equal 'III', to_roman(3)
       assert_equal 'IIII', to_roman(4)

       assert_equal 'VI', to_roman(6)
       assert_equal 'VII', to_roman(7)
       assert_equal 'VIII', to_roman(8)
       assert_equal 'VIIII', to_roman(9)

       assert_equal 'MDCCCCLXXXVIIII', to_roman(1989)
   end
end

2. to the actual solution:
(you'll be creating the number left-to-right)

*find largest digit less than the number. subtract its value from the
number, add the digit to the result*. repeat until the digit is larger
than the remainder. if there's anything left, choose the next digit.

in fact, the text between the stars is the simplest/most generic
algorithm. the following things are just an optimisation.

The actual ruby code I'll leave to you. First do anything that works
(use the test above to check, and add your own ones), no matter how
ugly it is. Then post your code, and somebody (be it me or anybody
else) will suggest you improvements.

3. a bit of rubyism:

instead of
def to_roman(int)
   ...
end

and calling as to_roman(123) you can extend the integers themselves:

class Integer
   def to_roman
   # use self insted of int parameter
   end
end

and call as 123.to_roman - it's nicer.