input: Write a function that takes an array of numbers and returns an array with the greatest and smallest values. If the input array is empty, return [0, 0].
  assert min_max([3, 4, 2, 8, 15, 6])==[2, 15]
  assert min_max([1, 2, 3, 4, 5])==[1, 5]
  assert min_max([-1, -5, -3, -2])==[-5, -1]
  assert min_max([])==[0, 0]
  def min_max(arr):
    if not arr:
      return [0, 0]
    min_val = min(arr)
    max_val = max(arr)
    return [min_val, max_val]
output: def min_max(arr):
    if not arr:
      return [0, 0]
    min_val = min(arr)
    max_val = max(arr)
    return [min_val, max_val]