text: '''
  Descripttion: 
  version: 
  Author: HuSharp
  Date: 2021-02-21 22:59:41
  LastEditors: HuSharp
  LastEditTime: 2021-02-21 23:12:36
  @Email: 8211180515@csu.edu.cn
  '''
  
  def countdown_1(k):
      if k > 0:
          yield k
          for i in countdown_1(k-1):
              yield i
  
  def countdown(k):
      if k > 0:
          yield k
          yield from countdown(k-1)
      else:
          yield 'Blast off'
  
  