input: 
  def min_max(arr: List[int]) -> List[int]:
      """ Return an array containing the smallest and greatest values from the input array.
      >>> min_max([3, 4, 2, 8, 15, 6])
      [2, 15]
      >>> min_max([1])
      [1, 1]
      >>> min_max([5, 5, 5, 5])
      [5, 5]
      """
      return [min(arr), max(arr)]
  
output:     return [min(arr), max(arr)]