PWC #340 (current) task #1 is to delete pairs of duplicate adjacent letters until none are left. I thought "maybe it's a good place to use a recursive pattern instead of (possibly) many loop iterations" Did I write it wrong? Is it just not applicable for tasks like these?

use strict;
use warnings;
use Time::HiRes 'time';

my $str;
$str .= chr 97 + rand 2 for 1 .. 5e3;

{
my $n = 0;
my $s = $str;
my $t = time;
$n ++ while $s =~ s/((.)(?1)?\2)//g;
printf qq(%3d loops, %.3f s, result: "%s"\n), $n, time - $t, $s
}

{
my $n = 0;
my $s = $str;
my $t = time;
$n ++ while $s =~ s/(.)\1//g;
printf qq(%3d loops, %.3f s, result: "%s"\n), $n, time - $t, $s
}

#  4 loops, 1.542 s, result: "babababa"
# 47 loops, 0.001 s, result: "babababa"

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In reply to Recursive sub-pattern spectacularly slow, what's wrong? (me, or just this use case, or a bug?) by Anonymous Monk

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