From: Mike Cargal <mike@...>
Date: 2010-11-05T07:53:56+09:00
Subject: Re: Regular Expression


On Nov 4, 2010, at 1:34 PM, Kendall Gifford wrote:

> On Thu, Nov 4, 2010 at 11:27 AM, Kendall Gifford <zettabyte@gmail.com> wrote:
>> On Thu, Nov 4, 2010 at 5:46 AM, Mike Cargal <mike@cargal.net> wrote:
>>> regex = /^(A(?!A)|B(?!B)|C(?!C)|D{1,2}(?!D))+$/
>>> 
>>> ["ABCDD","CA","CAD","CADD","CADDD","DAD","BAC","BBAD","AABCCD"].each do |string|
>>>   puts "'#{string}' => #{string.match(regex)}"
>>> end
>>> 
>>> ==============
>>> 'ABCDD' => ABCDD
>>> 'CA' => CA
>>> 'CAD' => CAD
>>> 'CADD' => CADD
>>> 'CADDD' =>
>>> 'DAD' => DAD
>>> 'BAC' => BAC
>>> 'BBAD' =>
>>> 'AABCCD' =>
>>> ==============
>> 
>> However, this also appears by my test to match "DADD", "ABA", etc:
>> 
>> ["ABA", "DADD", "CAC"].each do |string|
>>  puts "'#{string}' => #{string.match(regex)}"
>> end
>> 'DADD' => DADD
>> 'ABA' => ABA
>> 'CAC' => CAC
>> 
>> It does get you closer though. I rarely remember to make use of
>> look-ahead (and look-behind and other "(?X" style patterns) since when
>> switching languages/regexp engines, I'm never sure what features will
>> be there (and will still work the same). I guess I'm too conservative,
>> sticking with core/basic features.
>> 
>> This does make me curious how short of a regex using these features
>> could be written for this one case...
>> 
> 
> Okay, now this is even closer:
> 
> regex = /^(A(?=[^A]+$)|B(?=[^B]+$)|C(?=[^C]+$)|D{1,2}(?!D))+$/
> 
> However, it still has problems with "DADD", "DADBD" and such...
> 
> -- 
> Kendall Gifford
> zettabyte@gmail.com
> 


Oh... missed that detail... I *think* this covers the bases...


regex = /^(A(?!.*A)|B(?!.*B)|C(?!.*C)|D{1,2}(?!.*D))+$/

["ABCDD","CA","CAD",
  "CADD","CADDD","DAD",
  "BAC","BBAD","AABCCD",
  "DADD","DADBD","ABCDDA",
  "MIKE"].each do |string| 
   puts "'#{string}' => #{string.match(regex)}"
end
====================
'ABCDD' => ABCDD
'CA' => CA
'CAD' => CAD
'CADD' => CADD
'CADDD' => 
'DAD' => 
'BAC' => BAC
'BBAD' => 
'AABCCD' => 
'DADD' => 
'DADBD' => 
'ABCDDA' => 
'MIKE' => 
====================

Mike Cargal

mike@cargal.net
http://blog.mikecargal.com