Advent of code 2017/25

Ajax Direct

// Parse begin state
preg_match("/Begin in state (\w)/", $input->string, $state);
$state = $state[1];

// Parse steps
preg_match("/checksum after (\d+) steps/", $input->string, $steps);
$steps = (int) $steps[1];

// Parse states
$states = $input->lines->filter()->slice(2)->chunk(9)->mapAssoc(fn ($i, $state) => [
    $state[0][strlen($state[0]) - 2] =>
        $state->slice(1)->chunk(4)->mapAssoc(fn ($i, $chunk) => [
            $chunk[0][strlen($chunk[0]) - 2] => [
                $chunk[1][strlen($chunk[1]) - 2],               // Value
                substr($chunk[2], -6, -1) == "right" ? 1 : -1,  // Direction
                $chunk[3][strlen($chunk[3]) - 2]                // State
            ]
        ])
]);

$tape = [];
$pos  = 0;
for ($i = 0; $i < $steps; $i++) {
    $value = $tape[$pos] ?? 0;                  // Get value : 1 or 0
    $tape[$pos] = $states[$state][$value][0];   // Set value
    $pos += $states[$state][$value][1];         // Move pointer
    $state = $states[$state][$value][2];        // Change state
}

$solution_1 = array_sum($tape);
$solution_2 = "⭐";