new_contents: #!/usr/bin/env python3
  #-*- coding: utf-8 -*-
  
  from time import time
  
  def factorial(n):
      if n == 0:
          return 1
      else:
          return n * factorial(n - 1)
  
  # 查看算法运行时间
  start_time = time()
  print(factorial(100))
  end_time = time()
  elapsed = end_time - start_time
  print(elapsed)
  
subject: add factorial method and experimental studies