AoC 2025 day 3 regex version (Perl)

#!/usr/bin/perl

use strict;
use warnings;

use feature         qw(say);

# Change this to 2 for part 1
use constant LEN => 12;

#
# Mainline
#
my @input = map { chomp; $_ } <>;
my $part2 = 0;

# Create regex for finding first digit before a bigger digit
my $regex = '(?:' . join( '|', map { "[1-@{[$_-1]}](?=$_)" } (2 .. 9) ) . ')';

foreach my $queue (@input) {
    my @bank = split( //, substr( $queue, 0, -LEN, '' ) );

    while (my $jolts = pop @bank) {
        if ($jolts >= substr( $queue, 0, 1 )) {
            $queue = $jolts . $queue;           # add jolts to front
            $queue =~ s#$regex##;               # remove first digit followed by greater
        }
    }

    $part2 += substr( $queue, 0, LEN );         # truncate if needed
}

say "Part 2: $part2";