Advent of code 2016/12

Ajax Direct

function solve($input, $r) {

    for ($i = 0; $i < $input->lines->count(); $i++) {
        $c = explode(" ", $input->lines[$i]->string);

        switch ($c[0]) {
            case "cpy":
                $r[$c[2]] = $r[$c[1]] ?? $c[1]; break;
            case "inc":
                $r[$c[1]]++; break;
            case "dec":
                $r[$c[1]]--; break;
            case "jnz":
                if ($r[$c[1]] ?? $c[1]) $i += $c[2] - 1; break;
        }
    }

    return $r["a"];
}

// ==================================================
// > SOLUTIONS
// ==================================================
$r = array_fill_keys(["a", "b", "c", "d"], 0);
$solution_1 = solve($input, $r);

$r["c"] = 1;
$solution_2 = solve($input, $r);