Advent of code 2023/15

Ajax Direct

function num($string) {
    foreach (str_split($string) as $c) $sum = (($sum??0) + ord($c)) * 17 % 256;
    return $sum;
}

// ==================================================
// > PART 1
// ==================================================
$solution_1 = array_sum(array_map("num", explode(",", $input)));

// ==================================================
// > PART 2
// ==================================================
$boxes = [];

foreach (explode(",", $input) as $step) {
    preg_match("/([a-z]+)(=|-)([0-9]?)/", $step, $m);
    [$_, $label, $sign, $fl] = $m;
    $box = num($label);
    if ($sign == "-") {
        unset($boxes[$box][$label]);
    } else {
        $boxes[$box][$label] = $fl;
    }
}

$solution_2 = 0;
foreach ($boxes as $i=>$box) {
    $l = 1;
    foreach ($box as $label=>$fl) $solution_2 += ($i + 1) * $l++ * $fl;
}