Advent of code 2021/23

Ajax Direct

const PODS = [
    "A" => [0, 2, 1],
    "B" => [1, 4, 10],
    "C" => [2, 6, 100],
    "D" => [3, 8, 1000],
];
const NOSTOP = [2 => true, 4 => true, 6 => true, 8 => true];

function solve($start, $space) {

    return (new Graph(function ($graph) use ($space) {
        [$corr, $rooms] = explode("|", $graph->current);
        [$corr, $rooms] = [str_split($corr), str_split($rooms)];
        $next = [];

        // Consider rooms->corridor
        foreach ($rooms as $i=>$r) {
            if ($r == ".") continue;
            if ($i >= 4 && $rooms[$i - 4] != ".") continue;
            for ($j = $i; $j < $space*4; $j += 4) {
                if ($graph->end[12 + $j] != $rooms[$j]) break;
                if ($j >= ($space - 1) * 4) continue 2;
            }

            $c = ($i % 4) * 2 + 2;
            foreach ([[1, 11], [-1, -1]] as [$incr, $bound]) {
                for ($j = $c; $j != $bound; $j += $incr) {
                    if ($corr[$j] != ".") break;
                    if (isset(NOSTOP[$j])) continue;
                    $state = $graph->current;
                    $state[$j] = $r;
                    $state[$i + 12] = ".";
                    $next[$state] = ((floor($i/4)+1) + abs($c - $j)) * PODS[$r][2];
                }
            }
        }

        // Consider corridor->room
        foreach ($corr as $i=>$c) {
            if ($c == ".") continue;
            if ($rooms[PODS[$c][0]] != ".") continue;

            for ($f = $space - 1; $f >= 0; $f--) {
                $t = PODS[$c][0] + $f*4;
                if ($rooms[$t] == ".") break;
                if ($rooms[$t] != $c) continue 2;
                if (!$f) continue 2;
            }

            foreach (range($i, PODS[$c][1]) as $p) {
                if ($i == $p) continue;
                if ($corr[$p] != ".") continue 2;
            }

            $state = $graph->current;
            $state[$i] = ".";
            $state[PODS[$c][0] + (4*$f) + 12] = $c;
            $next[$state] = (abs($i-PODS[$c][1]) + 1 + $f) * PODS[$c][2];
        }

        return $next;
    }))
    ->explore(
        "...........|".$start,
        "...........|".str_repeat("ABCD", $space),
    )[1];
}

// ==================================================
// > SOLVE
// ==================================================
$letters = implode("", $input->matchAll("/[A-D]/")[0]);
$solution_1 = solve($letters, 2);
$solution_2 = solve(substr($letters, 0, 4) . "DCBADBAC" . substr($letters, 4, 4), 4);