in reply to Re^2: substrings that consist of repeating characters
in thread substrings that consist of repeating characters

Does that work? 

Win8 Strawberry 5.30.3.1 (64)  Tue 09/29/2020 13:32:10
C:\@Work\Perl\monks
>perl
use strict;
use warnings;

my $string = 'AABBBBCCC';

my $len = 0;
my $best = "";
while ($string =~ /((.)(?:(*SKIP)\2){$len,})/g) {
    $len = length $1;
    $best = $1
}

print "best: '$best' \n"

^Z
best: ''

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Re^4: substrings that consist of repeating characters
by salva (Canon) on Sep 29, 2020 at 20:59 UTC
    Oops, no, it doesn't, but I think it should!

    Is that a bug in perl?

[reply]
      I tried turning 
      use re 'debug';

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      on and comparing the output with 
      /((.)(?:\2(*SKIP)){$len,})/g

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      which seems to work, but I don't understand the output enough to be able to explain why the behaviour is different.

      map{substr$_->[0],$_->[1]||0,1}[\*||{},3],[[]],[ref qr-1,-,-1],[{}],[sub{}^*ARGV,3]
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        Aja, that has allowed me to see the problem!

        The (*SKIP) inside the repetition always matches, but once the end of the same-char sequence is reached the \2 fails, so it causes the repetition to backtrack, but it can't because of the (*SKIP), so all the repetition fails!

        Moving the (*SKIP) after the \2 fixes the issue: 

        my $string = "ATTTAGTTCTTAAGGCTGACATCGGTTTACGTCAGCGTTACCCCCCAAGTTTTTTT
+TTTTTTTTTTTATTGGGGACTTT";

my $len = 0;
my $best = "";
while ($string =~ /((.)(\2(*SKIP)){$len,})/g) {
    $len = length $1;
    $best = $1
}

print "best: $best\n"

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