AoC day 23 (pt1), Perl

#!/usr/bin/perl

use strict;
use warnings;

my @ring;
my ($curr, $prev);

# Read in file, building ring
chomp( my $input = <> );
foreach (split( //, $input )) {
    $curr //= $_;
    $ring[$prev] = $_  if (defined $prev);
    $prev = $_;
}
$ring[$prev] = $curr;

# run 100 turns
foreach (1 .. 100) {
    # Advance ptr marking cups (cup 0 doesn't exist, marked as "grabbed" too)
    my $ptr = $curr;
    my %grab = (0 => 1, map { $ptr = $ring[$ptr]; $ptr => 1 } (1 .. 3));

    # Calculate destination (assuming cups 1-9 in input)
    my $dest = $curr - 1;
    $dest = ($dest - 1) % 10 while (exists $grab{$dest});

    # Relink ring
    ($ring[$curr], $ring[$ptr], $ring[$dest]) = ($ring[$ptr], $ring[$dest], $ring[$curr]);

    $curr = $ring[$curr];
}

print "Part 1: ";
$curr = 1;
print $curr while (($curr = $ring[$curr]) != 1);
print "\n";