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Re^5: substrings that consist of repeating characters

by choroba (Cardinal)
on Sep 29, 2020 at 21:20 UTC ( [id://11122351]=note: print w/replies, xml ) Need Help??


in reply to Re^4: substrings that consist of repeating characters
in thread substrings that consist of repeating characters

I tried turning 
use re 'debug';

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

[download]
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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Re^6: substrings that consist of repeating characters
by salva (Canon) on Sep 30, 2020 at 07:32 UTC
    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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