code: def common_array(ary) # rubocop: disable AbcSize
        return ary unless ary.is_a? Array
        count = ary.count
        return ary if count.zero?
        return ary.flatten.uniq if count == 1
        common = ary[0] & ary[1]
        return common if count == 2
        (count - 2).times { |x| common &= ary[x + 2] } if count > 2
        common
      end
docs: => Return Common Elements of an Array