ruby    def ten_thouusand_ceil(n)
        (n.fp 10000).ceil * 10000
    end

2.1.5 :015 > ten_thouusand_ceil 4001 => 10000
2.1.5 :016 > ten_thouusand_ceil 5010 => 10000
2.1.5 :017 > ten_thouusand_ceil 10001 => 20000

可以这样

def get_num(n)
  while j ||= 0
    return 10**j if n <= 10**j
    j = j + 1
  end
end