comefrom: <qiyuangong>268_Missing_Number_1.py
code: def missingNumber( nums):
      n = len(nums)
      return (n ** 2 + n) / 2 - sum(nums)
masked: def sample_funcname ( var_0 ) :
      var_2 = len ( var_0 )
      return ( var_2 ** 2 + var_2 ) / 2 - sum ( var_0 )
  