fibonacci regex


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fibonacci regex

by mauke (Novice)

on Jan 25, 2005 at 13:54 UTC ( #424865=snippet: print w/replies, xml )

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Description:

Writing your own regex library can help you understand some of the more obscure features of Perl's regexes. :-)
The following regex matches lines consisting of words whose length form the fibonacci sequence 1, 1, 2, 3, 5, 8, 13, etc. Caveat: All words must consist of the same character.

Examples of valid input:
v
x x xx xxx xxxxx

Ok, it's probably not very useful, but I thought I'd post it anyway.

#!/usr/local/bin/perl
use warnings;
use strict;

while (<>) {
    print "fibo\n" if /^\s*(?:((?(1)(?(3)(?(2)\2|\3)(\1)|(\S))|\S))\s+
+)+\z/;
}

Comment on fibonacci regex Download Code

Replies are listed 'Best First'.
Re: fibonacci regex by TedYoung (Deacon) on Jan 25, 2005 at 15:39 UTC
Nice, this reminds me of a function to test if a number if prime: `sub isPrime { ('1' x $_[0]) !~ /^(11+)\1+$/; }` [download] Ted Young `($$<<$$=>$$<=>$$<=$$>>$$) always returns 1. :-)`	[reply] [d/l] [select]
Re^2: fibonacci regex by ambrus (Abbot) on May 10, 2010 at 19:27 UTC
See also prime factorization using base 1 for the original source, and Re: Simple primality testing.	[reply]

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