<?php
$input_file = '../inputs/day10.txt';
if (file_exists($input_file)) {
	$input = file_get_contents($input_file);
	if ($input != null) {
		$joltages = array_map('trim', explode("\n", $input));
		print 'Part 1 answer: ' . solve_part_one($joltages) . "\n";
		print 'Part 2 answer: ' . solve_part_two($joltages) . "\n";
	}
}

function solve_part_one(array $joltages): int
{
	$sorted_joltages = $joltages;
	$sorted_joltages[] = "0";
	sort($sorted_joltages);
	$sorted_joltages[] = $sorted_joltages[count($sorted_joltages) - 1] + 3;
	$differences = chain_adapters($sorted_joltages);
	return $differences[0] * $differences[2];
}

function solve_part_two(array $joltages): int
{
	$sorted_joltages = $joltages;
	$sorted_joltages[] = "0";
	sort($sorted_joltages);
	$sorted_joltages[] = $sorted_joltages[count($sorted_joltages) - 1] + 3;
	return get_max_chains($sorted_joltages);
}

function chain_adapters(array $joltages): array
{
	$differences = [0, 0, 0];

	for ($i = 1; $i < count($joltages); $i++) {
		$diff = $joltages[$i] - $joltages[$i - 1];
		$differences[$diff - 1] += 1;
	}

	return $differences;
}

function get_max_chains(array $joltages): int
{
	$jolt_count = count($joltages);
	$memo = [$jolt_count - 1 => 1];

	for ($i = $jolt_count - 2; $i >= 0; $i--) {
		$count = 0;
		for ($j = $i + 1; $j < $jolt_count && $joltages[$j] - $joltages[$i] <= 3; $j++) {
			$count += $memo[$j];
		}
		$memo[$i] = $count;
	}

	return $memo[0];
}