input: Write a python function to normalize a vector.
  assert normalize([1, 5, 2, 8, 9, 4]) == [0.10938925979875006, 0.5469462984987499, 0.21877851959750005, 0.8750559279949998, 0.9845033377885005, 0.43693269989949995]
  assert normalize([3, 4]) == [0.6, 0.8]
  assert normalize([0, 0, 0]) == [0, 0, 0]
output: def normalize(vector):
      import math
      norm = math.sqrt(sum(x**2 for x in vector))
      if norm == 0:
          return [0] * len(vector)
      return [x / norm for x in vector]