<?php
$input_file = '../inputs/day15.txt';
if (file_exists($input_file)) {
	$input = file_get_contents($input_file);
	if ($input != null) {
		$numbers = array_map('trim', explode(',', $input));
		print 'Part 1 answer: ' . solve_part_one($numbers) . "\n";
		print 'Part 2 answer: ' . solve_part_two($numbers) . "\n";
	}
}

function solve_part_one(array $numbers): int
{
	return get_number_in_sequence($numbers, 2020);
}

function solve_part_two(array $numbers): int
{
	ini_set('memory_limit', '-1');
	return get_number_in_sequence($numbers, 30000000);
}

function get_number_in_sequence(array $initial_numbers, int $num): int
{
	$last_spoken = [];
	foreach ($initial_numbers as $turn => $number)
		$last_spoken[(int)$number] = (int)$turn + 1;

	$last = array_keys($last_spoken)[count($last_spoken) - 1];

	for ($i = count($last_spoken); $i < $num; $i++) {
		if (array_key_exists($last, $last_spoken)) {
			$prev = $last;
			$last = $i - $last_spoken[$last];
			$last_spoken[$prev] = $i;
		} else {
			$last_spoken[$last] = $i;
			$last = 0;
		}
	}

	return $last;
}