From: w_a_x_man <w_a_x_man@...>
Date: 2010-11-04T01:45:22+09:00
Subject: Re: Regular Expression

On Nov 3, 7:31 am, Robert Klemme <shortcut...@googlemail.com> wrote:
> 2010/11/3 Jesús Gabriel y Galán <jgabrielyga...@gmail.com>:
>
>
>
>
>
> > On Wed, Nov 3, 2010 at 11:10 AM, Robert Klemme
> > <shortcut...@googlemail.com> wrote:
> >> Interesting approach.  I would simply have done
>
> >> def check(input)
> >>  raise ArgumentError, "Illegal chars in sequence: %p" % input unless
> >> /\A[A-D]{0,4}\z/ =~ input
> >>  cnt = Hash.new 0
> >>  input.scan /./ do |m|
> >>    raise ArgumentError, "Illegal sequence %p" % input if (cnt[m] += 1) > 1
> >>    # alt: return false
> >>  end
> >>  # alt: true
> >> end
>
> > There are different requirements for each letter. Adapting your solution:
>
> Good point!  I overlooked that.
>
> > def check(input)
> >  limits = {'A' => 1, 'B' => 1, 'C' => 1, 'D' => 2}
> >  raise ArgumentError, "Illegal chars in sequence: %p" % input unless
> > /\A[A-D]{0,4}\z/ =~ input
> >  cnt = Hash.new 0
> >  input.scan /./ do |m|
> >    cnt[m] += 1
> >  end
>
> >  cnt.each do |letter, amount|
> >    raise ArgumentError, "Illegal chars in sequence: %p" % input if
> > amount > limits[letter]
> >  end
> > end
>
> I'd rather do:
>
> def check(input)
>  raise ArgumentError, "Illegal chars in sequence: %p" % input unless
> /\A[A-D]{0,4}\z/ =~ input
>  cnt = {'A' => 1, 'B' => 1, 'C' => 1, 'D' => 2}
>  input.scan /./ do |m|
>    raise ArgumentError, "Illegal sequence %p" % input if (cnt[m] -= 1) < 0
>    # alt: return false
>  end
>  # alt: true
> end

"We don't need no stinkin' loops!"


def check input
  return false  unless /\A[A-D]{0,4}\z/ =~ input
  %w(A B C D).map{|s| input.count s}.zip( [1,1,1,2] ).
    map{|a,b| b-a}.all?{|n| n >= 0}
end