From: dblack@...
Date: 2002-10-15T11:00:21+09:00
Subject: Re: Please check my algorithm

Hi --

On Tue, 15 Oct 2002, Vincent Foley wrote:

> Hi, I found a nice programming challenge:
> http://acm.uva.es/p/v3/333.html

That is quite a cool one.

> I have written an entry in Ruby, and I'd like to know if there are
> things I could improve.
>
> #!/usr/bin/env ruby
>
> class ISBN
>   def initialize(code)
>     @code = code
>   end
>
>   def calc(lst)
>     ans = []
>     ans[0] = lst[0]
>     for i in 1...lst.length
>       ans[i] = ans[i-1] + lst[i]
>     end
>     ans
>   end

This struck me as a good candidate for the new #inject method, though
that's only in 1.7.  (See below.)

>   def validChars
>     stripCode = @code.tr("-", "")
>     if stripCode =~ /^[0-9]{9}[0-9X]$/i
>       true
>     else
>       false
>     end
>   end

Unless you really need 'true' and 'false', you could just do:

  def valid_chars
    /^\d{9}[\dX]$/i.match(@code.delete("-"))
  end

and let the MatchData/nil distinction serve for the Boolean test.

(OK, I admit I'm slipping in some subliminal antiCamelCase
propaganda :-)

>
>   def validate
>     if validChars then
>       stripCode = @code.tr("-", "")

You've got that twice; you might want to have a separate method, or
instance variable, for the tr'd version.

> [...]

Well, for what it's worth, here's my 1.7-only version (it uses
#inject).  I can't help feeling there's a way to do some kind of
double inject, and avoid using the 't' accumulator... but anyway, here
is its current incarnation:

#!/usr/local/lib/ruby/1.7/bin/ruby -w

  class ISBN < String

    ISBN_RE = /^\s*(\d-?){9}(X|\d)\s*$/

    def check
      t = 0
      ISBN_RE.match(self) &&
	numbers.inject(0) {|x,y| t += x+y; x+y } &&
	(t % 11) .zero?
    end

    def numbers
      strip.delete('-').split(//).map {|i| i.sub(/X/,"10").to_i}
    end

  end

  p ISBN.new("0-89237-010-6").check  # true
  p ISBN.new("0-89237-010-5").check  # false
  p ISBN.new("blah").check           # nil

__END__

(The nil/false thing could be smoothed out if necessary.)


David

-- 
David Alan Black
home: dblack@candle.superlink.net
work: blackdav@shu.edu
Web:  http://pirate.shu.edu/~blackdav