From: Marko Schulz <in6x059@...>
Date: 2001-12-20T16:57:06+09:00
Subject: [ruby-talk:29083] Math with RexExps (was:  Re: But is it Fun?)

On Thu, Dec 20, 2001 at 12:39:08PM +0900, Michael Cook wrote:
> 
> ruby -le '$_ = 1; ("1" * $_) !~ /^(11+)\1+$/ && print while $_ += 1'

Looking closer at how you are computing primes with a regular expression:

Changing your
   /^(11+)\1+$/
into 
   /^(1{2,})\1+$/
still lets the program run correctly.

But when I tried the following
   /^(1{2,}){2,}$/
it didn't anymore. 

Is Rubys (1.6.5) RE-engine doing not enough backtracking for this?

-- 
marko schulz