day6.php

<?php
declare(strict_types=1);

$input = file('input.txt');
//$input = file('sample.txt');
$times = array_filter(explode(' ', trim(substr($input[0], strpos($input[0], ':') + 1))));
$distances = array_filter(explode(' ', trim(substr($input[1], strpos($input[1], ':') + 1))));

$races = array_combine($times, $distances);
$part1Answer = 1;
foreach ($races as $time => $distance) {
    $part1Answer *= findPossibleWinningRaceCount(intval($time), intval($distance));
}
printf('Part 1 answer: %s' . PHP_EOL, $part1Answer);

$time = str_replace(' ', '', substr($input[0], strpos($input[0], ':') + 1));
$distance = str_replace(' ', '', substr($input[1], strpos($input[1], ':') + 1));

printf('Part 2 answer: %s' . PHP_EOL, findPossibleWinningRaceCount(intval($time), intval($distance)));

function findPossibleWinningRaceCount(int $timeInMs, int $distanceInMm): int
{
    printf('Finding ways to beat record of %d mm in %d ms...' . PHP_EOL, $distanceInMm, $timeInMs);
    $possibleWinCount = 0;
    for ($holdTime = 1; $holdTime < $timeInMs; $holdTime++) {
        $raceTime = $timeInMs - $holdTime;
        $raceDistance = $raceTime * $holdTime;
        if ($raceDistance > $distanceInMm) {
            $possibleWinCount++;
            //printf('winning: holding button for %d ms gives a distance of %s!' . PHP_EOL, $raceTime, $raceDistance);
        }
    }

    if ($possibleWinCount === 0) {
        printf('none found :(' . PHP_EOL);
    } else {
        printf('there are %d ways' . PHP_EOL, $possibleWinCount);
    }

    return $possibleWinCount;
}

function dd($a, $b = null, $c = null, $d = null): void
{
    die(var_dump($a, $b, $c, $d));
}