in reply to Re^2: Finding repeat sequences.
in thread Finding repeat sequences.

here a regex solution which works for the shortest possible tail of length k

  DB<127> $str
 => "abcdabcdabceabcdabcdabceab"

  DB<128> $str=~/^((.+?).*)\2$/; $rest=$1, $tail=$2 
 => ("abcdabcdabceabcdabcdabce", "ab")

  DB<129> $rest =~ /^(.+?)\1*$/; $1
 => "abcdabcdabce"

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needs to be extended for longer possible tails.

But taking the dimensions of your data I doubt that regexes are appropriate.

You could test all $patterns which repeat at least once (or x times) and calculate $k = $m % $l with $m =length ($str), and check if $str starts and ends with the same substring $tail of length $k and then check if the pattern continues repeating.

Or start eliminating all possible $tails and check if $l of a repeating pattern is a divisor of the $rest.

Had no time to check all the other posted solutions and don't wanna reinvent the wheel, so I better stop here! =)

HTH

Cheers Rolf

( addicted to the Perl Programming Language)

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Re^4: Finding repeat sequences.
by BrowserUk (Patriarch) on Jun 21, 2013 at 02:48 UTC

    That looks suspiciously like a close variation on choroba's attempt.

    Had no time to check all the other posted solutions and don't wanna reinvent the wheel,

    All the tested solutions, along with how they faired in my test harness, are nicely grouped together in Re: Finding repeat sequences. (Results:Part 1).

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