AoC 2024, day 9, part 1 (Perl)

#!/usr/bin/perl

use strict;
use warnings;

use feature         qw(say);
use List::Util      qw(sum);

my @input = map { chomp; split // } <>;

my @disk;
my $id = 0;
while (@input) {
    my $size = shift @input;
    my $gap  = shift @input;

    push( @disk, ($id++) x $size );
    push( @disk, ('.')   x $gap  )   if ($gap);
}

my $left  = 0;
my $right = $#disk;

while (1) {
    $left++   while ($disk[$left]  ne '.');
    $right--  while ($disk[$right] eq '.');

    last if ($left >= $right);

    $disk[$left]  = $disk[$right];
    $disk[$right] = '.';
}

say "Part 1: ", sum map { ($disk[$_] ne '.') ? $_ * $disk[$_] : 0 } (0 .. $left);