day-21.php

<?php

$input = trim(file_get_contents('input/' . substr(basename(__FILE__), 0, -4)));
$start = microtime(true);
$input = explode("\n", $input);

$functions = [
    'addr' => function($a, $b, $c, array &$reg) { $reg[$c] = $reg[$a] + $reg[$b]; },
    'addi' => function($a, $b, $c, array &$reg) { $reg[$c] = $reg[$a] + $b; },
    'mulr' => function($a, $b, $c, array &$reg) { $reg[$c] = $reg[$a] * $reg[$b]; },
    'muli' => function($a, $b, $c, array &$reg) { $reg[$c] = $reg[$a] * $b; },
    'banr' => function($a, $b, $c, array &$reg) { $reg[$c] = $reg[$a] & $reg[$b]; },
    'bani' => function($a, $b, $c, array &$reg) { $reg[$c] = $reg[$a] & $b; },
    'borr' => function($a, $b, $c, array &$reg) { $reg[$c] = $reg[$a] | $reg[$b]; },
    'bori' => function($a, $b, $c, array &$reg) { $reg[$c] = $reg[$a] | $b; },
    'setr' => function($a, $b, $c, array &$reg) { $reg[$c] = $reg[$a]; },
    'seti' => function($a, $b, $c, array &$reg) { $reg[$c] = $a; },
    'gtir' => function($a, $b, $c, array &$reg) { $reg[$c] = $a > $reg[$b] ? 1 : 0; },
    'gtri' => function($a, $b, $c, array &$reg) { $reg[$c] = $reg[$a] > $b ? 1 : 0; },
    'gtrr' => function($a, $b, $c, array &$reg) { $reg[$c] = $reg[$a] > $reg[$b] ? 1 : 0; },
    'eqir' => function($a, $b, $c, array &$reg) { $reg[$c] = $a === $reg[$b] ? 1 : 0; },
    'eqri' => function($a, $b, $c, array &$reg) { $reg[$c] = $reg[$a] === $b ? 1 : 0; },
    'eqrr' => function($a, $b, $c, array &$reg) { $reg[$c] = $reg[$a] === $reg[$b] ? 1 : 0; },
];

$ipValue = (int) explode(' ', array_shift($input))[1];
$program = [];

foreach ($input as $line) {
    $part = explode(' ', $line);
    $program[] = [$part[0], (int) $part[1], (int) $part[2], (int) $part[3]];
}
$steps = count($program);

$pointer = -1;
$registers = [0, 0, 0, 0, 0, 0];
$counter = 0;
$values = [];

while (++$pointer < $steps) {
    $instr = $program[$pointer];
    $registers[$ipValue] = $pointer;
    $functions[$instr[0]]($instr[1], $instr[2], $instr[3], $registers);
    $pointer = $registers[$ipValue];

    if ($pointer === 28) {
        if (!isset($values[$registers[3]])) {
            $values[$registers[3]] = $counter;
        } else {
            break;
        }
    }

    if ($counter++ > 50 && $pointer === 17) {
        $registers[1] = floor($registers[2] / 256);
    }
}

asort($values);

reset($values);
echo 'Answer 1: ' . key($values) . PHP_EOL;
end($values);
echo 'Answer 2: ' . key($values) . PHP_EOL;

echo 'Execution time: ' . (microtime(true) - $start) . PHP_EOL;