#!/usr/bin/perl
use v5.35.0;
use List::Util 'sum';

# Code mine, algorithm not. Based on a reddit comment here:
# https://www.reddit.com/r/adventofcode/comments/1hbqt2e/comment/m1j6c5s/

my $stones = {};
while (<>) {
	while (/(\d+)/g) {
		$$stones{$1}++;
	}
}

for (1 .. 75) {
	my $new_stones = {};
	while (my ($engraving, $count) = each %$stones) {
		if ($engraving == 0) {
			$$new_stones{1} += $count;
		} else {
			my $len = length($engraving);
			if ($len % 2 == 0) {
				$len /= 2;
				$$new_stones{0 + substr($engraving, 0, $len)} += $count;
				$$new_stones{0 + substr($engraving, $len)} += $count;
			} else {
				$$new_stones{$engraving * 2024} += $count;
			}
		}
	}
	$stones = $new_stones; # blink!
}

say sum(values %$stones)