Roman Numerals (Arrgh!)

ruby-talk
21

I didn't miss it at all, it's quite cool, but very not easy to find directly
and to explain for an homework ...

But I admit it's quite a nice solution, not that hard to understand.

···

2009/11/11 Gennady Bystritsky <Gennady.Bystritsky@quest.com>

On Nov 11, 2009, at 11:59 AM, Benoit Daloze wrote:

> Well, being student as well, I'd love to study Ruby instead of this
(****)
> Java. (Where are you studying?) But that's not the point.
>
> So, here is my piece of advice:
>
> Using $numerals = [
> [1000, "M"], [900, "CM"], [500, "D"], [400, "CD"],
> [100, "C"], [90, "XC"], [50, "L"], [40, "XL"],
> [10, "X"], [9, "IX"], [5, "V"], [4, "IV"],
> [1, "I"]
> ]
>
> ,you should iterate on each of them, seeing how much your number have of
> this kind (/)
> and what is the rest after that, to use it for the next step(%)...
> (if you use Array#each, you'll get a new array(let's say a) like a=[dec,
> romanString]. You can then take them separetely by a[0] and a[1].
> Even if this method is not that beautiful in Ruby, it's the easiest way
to
> understand how to do it).
>
> That the way used in a very known book of Ruby.
>
> You just need to manage how to save this in your String at each step.
> (You can multiply a String by "X" * 3, and concatenate using << (or +=))
>
> Give us your script when you'll got one working :wink:

In case you have missed it from yesterday, a slightly modified original
solution was:

def roman_numeral(number)
$numerals.inject(["", number]) { |(result, number), (order, roman)|
   [ result + roman * (number / order), number % order ]
}.first
end

It works with shortened numerals for 4, 9, 40, 90, 400, 900 as well.

Gennady.

22

Benoit Daloze wrote:

I didn't miss it at all, it's quite cool, but very not easy to find
directly
and to explain for an homework ...

But I admit it's quite a nice solution, not that hard to understand.

I'm going to assume the assignment has long been completed, so here is
how I would have written the function. Not as elegant as the inject
version above, but simpler for someone new to Ruby (like myself) to
understand.

def roman_numeral(number)
  result, numerals = "", [
    [1000, "M"], [900, "CM"], [500, "D"], [400, "CD"],
    [100, "C"], [90, "XC"], [50, "L"], [40, "XL"],
    [10, "X"], [9, "IX"], [5, "V"], [4, "IV"],
    [1, "I"]
  ]
  numerals.each do |order, roman|
    result << roman * (number / order)
    number %= order
  end
  result
end

···

2009/11/11 Gennady Bystritsky <Gennady.Bystritsky@quest.com>

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