Advent of code 2021/22

Ajax Direct

/**
 * Return the cuboid intersection of two cuboids,
 * plus all remaining cuboids resulting from their difference
 *
 * @param array $c1 Subject cuboid
 * @param array $c2 Difference cuboid
 * @return array [intersection, remaining cuboids]
 */
function cube_intersect($c1, $c2)
{
    // Fully outside : no intersection
    foreach ([0, 2, 4] as $ax) {
        if ($c2[$ax+1] < $c1[$ax] && $c2[$ax+1] < $c1[$ax+1]) return [[], [$c1]];
        if ($c2[$ax] > $c1[$ax] && $c2[$ax] > $c1[$ax+1]) return [[], [$c1]];
    }

    // Find intersection cube
    $int = [];
    foreach ([0, 2, 4] as $ax) {
        $int[] = $c2[$ax] > $c1[$ax] ? $c2[$ax] : $c1[$ax];
        $int[] = $c2[$ax+1] < $c1[$ax+1] ? $c2[$ax+1] : $c1[$ax+1];
    }

    // Split on each axis
    $cubes = [$c1];
    foreach ([0, 2, 4] as $ax) {
        $cube = array_shift($cubes);
        [$ca, $cb] = [$cube[$ax], $cube[$ax+1]];
        [$ia, $ib] = [$int[$ax], $int[$ax+1]];

        $ax_split = [[$ia, $ib]];
        if ($ca < $ia) $ax_split[] = [$ca, $ia-1];
        if ($cb > $ib) $ax_split[] = [$ib+1, $cb];

        $cube_split = [];
        foreach ($ax_split as $asp) {
            $ncube = $cube;
            $ncube[$ax] = $asp[0];
            $ncube[$ax+1] = $asp[1];
            $cube_split[] = $ncube;
        }

        $cubes = array_merge($cube_split, $cubes);
    }

    return [array_shift($cubes), $cubes];
}


function solve($part1) {
    global $input;
    $on = [];

    foreach ($input->lines as $line) {
        $new_on = [];

        $zone = (array) $line->numbers();
        if ($part1 && ($zone[0] < -50 || $zone[0] > 50)) break;
        if ($line->split(" ")[0] == "on") $new_on[] = $zone;

        foreach ($on as $other_zone) {
            $new_on = array_merge($new_on, cube_intersect($other_zone, $zone)[1]);
        }
        $on = $new_on;
    }

    return array_reduce($on, function ($carry, $c) {
        return $carry + abs($c[0]-$c[1]-1) * abs($c[2]-$c[3]-1) * abs($c[4]-$c[5]-1);
    }, 0);
}


// ==================================================
// > SOLUTION
// ==================================================
$solution_1 = solve(true);
$solution_2 = solve(false);