input: Write a python function to classify a list of numbers into categories zero, one, two, and three.
  assert classify([1, 2, 0, 1, 3, 2]) == {'zero': [0], 'one': [1, 1], 'two': [2, 2], 'three': [3]}
  assert classify([0, 0, 0, 1, 1, 2, 3, 3]) == {'zero': [0, 0, 0], 'one': [1, 1], 'two': [2], 'three': [3, 3]}
  assert classify([3, 3, 3, 2, 2, 1, 0]) == {'zero': [0], 'one': [1], 'two': [2, 2], 'three': [3, 3, 3]}
output: def classify(numbers):
      categories = {'zero': [], 'one': [], 'two': [], 'three': []}
      for number in numbers:
          if number == 0:
              categories['zero'].append(number)
          elif number == 1:
              categories['one'].append(number)
          elif number == 2:
              categories['two'].append(number)
          elif number == 3:
              categories['three'].append(number)
      return categories