text: """ This problem was asked by Goldman Sachs.
  
  Given a list of numbers L, implement a method sum(i, j) which returns 
  the sum from the sublist L[i:j] (including i, excluding j).
  
  For example, given L = [1, 2, 3, 4, 5], sum(1, 3) should return sum([2, 3]), which is 5.
  
  You can assume that you can do some pre-processing. 
  sum() should be optimized over the pre-processing step.
  """
  