function dominator(array $a): int
{
    $size  = $value = $count = 0;
    $index = 0;
    foreach ($a as $k => $v) {
        if ($size === 0) {
            $size++;
            $value = $v;
            $index = $k;
        } elseif ($value !== $v) {
            $size--;
        } else {
            $size++;
        }
    }
    $candidate = $size > 0 ? $value : -1;

    foreach ($a as $v) {
        if ($v === $candidate) {
            $count++;
        }
    }
    if ($count <= count($a) / 2) {
        $index = -1;
    }

    return $index;
}