Hello rsFalse,

First, the code you have does not appear to be producing correct results. For example, you have this line of input:

()(())()

[download]

which produces:

8 1

[download]

but by inspection we can see that the longest subsequence of validly-nested parentheses is (()) which is only 4 characters long.

Second, as Eily says you can get a significant speedup by using (?PARNO). For example, adapting the code in Can-I-use-Perl-regular-expressions-to-match-balanced-text of perlfaq6, I came up with this:

use strict;
use warnings;
use List::Util 'max';

srand;
my @lines = <DATA>;
my $n     = 1000;
my $long  = '';
   $long .= qw{( )}[ int(rand() * 2) ] for 1 .. $n;
my $regex =
qr{
    (                       # start of capture group 1
        \(                  # match an opening parenthesis
            (?:
                [^()]++     # one or more non-parentheses, non backtra
+cking
                |           # OR
                (?1)        # recurse to capture group 1
            )*
        \)                  # match a closing parenthesis
    )                       # end of capture group 1
}x;

for my $string (@lines, $long)
{
    my $max    = 0;
    my $occ    = 1;
    my @groups = $string =~ m/$regex/g;

    if (@groups)
    {
        @groups = sort { length $a <=> length $b } @groups;
        $max = length $groups[-1];

        for my $i (reverse 0 .. $#groups - 1)
        {
            if (length $groups[$i] == length $groups[-1])
            {
                ++$occ;
            }
            else
            {
                last;
            }
        }
    }

    print "$max $occ\n";
}

__DATA__
)((())))(()())
))(
()(())()
((((()(((
(()())()(())()()())())()((()(()(())()()())((()(())()(()()()()))()(())(
+)(((()())()(()((())()(())(()))

[download]

Typical output:

23:28 >perl 1071_SoPW.pl
6 2
0 1
4 1
2 1
20 1
266 1

23:28 >

[download]

For a long string this is much faster than using (??{ code }).

Hope that helps,

Athanasius <°(((>< contra mundum Iustus alius egestas vitae, eros Piratica,

In reply to Re: how to speed up that dynamic regex? by Athanasius
in thread how to speed up that dynamic regex? by rsFalse

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