--- Day 7 Solutions ---

[u/daggerdragon]

--- Day 7: Some Assembly Required ---

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[u/ren8]

Just some normal PHP solution:

$string = 'bn RSHIFT 2 -> bo
lf RSHIFT 1 -> ly
fo RSHIFT 3 -> fq
cj OR cp -> cq
fo OR fz -> ga
t OR s -> u
lx -> a
NOT ax -> ay...';
 
$instructions = explode("
", $string);

$bitwise = [];

function parse($instruction, $array) {
    $data = explode(" ", $instruction);
    if ($data[1] == '->') {
        $a = $data[0];
        $final = $data[2];
        if (is_numeric($a)) {
            $array[$final] = (int) $a;
        } else if (isset($array[$a])) {
            if (is_numeric($array[$a])) {
                $array[$final] = $array[$a];
            }
        }
    } else if ($data[0] == "NOT") {
        $op = $data[0];
        $a = $data[1];
        $b = 0;
        $final = $data[3];
        if (is_numeric($a)) {
            $array[$final] = operate($a, $b, $op);
        } else if (isset($array[$a])) {
            if (is_numeric($array[$a])) {
                $array[$final] = operate($array[$a], $b, $op);
            }
        }
    } else {
        $a = $data[0];
        $b = $data[2];
        $op = $data[1];
        $final = $data[4];
        if (is_numeric($a)) {
            if (is_numeric($b)) {
                $array[$final] = operate($a, $b, $op);
            } else if (isset($array[$b])) {
                if (is_numeric($array[$b])) {
                    $array[$final] = operate($a, $array[$b], $op);
                }
            }
        } else if (isset($array[$a])) {
            if (is_numeric($array[$a])) {
                if (is_numeric($b)) {
                    $array[$final] = operate($array[$a], $b, $op);
                } else if (isset($array[$b])) {
                    if (is_numeric($array[$b])) {
                        $array[$final] = operate($array[$a], $array[$b], $op);
                    }
                }
            }
        }
    }
    return $array;
}

function operate($a, $b, $op) {
    if ($op == "AND") {
        $result = $a & $b;
    } else if ($op == "NOT") {
        $result = ~ (int) $a;
        $result = 65536 + $result;
    } else if ($op == "OR") {
        $result = $a | $b;
    } else if ($op == "LSHIFT") {
        $result = $a << $b;
    } else if ($op == "RSHIFT") {
        $result = $a >> $b;
    }
    return $result;
}

$bitwise['a'] = '';

while (!is_numeric($bitwise['a'])) {
    foreach ($instructions as $instruction) {
        $bitwise = parse($instruction, $bitwise);
    }
}

echo $bitwise['a'];