input: Write a function to return an array containing the minimum and maximum values from the input array.
  def min_max(arr):
    min_val = min(arr)
    max_val = max(arr)
    return [min_val, max_val]
  
  assert min_max([3, 4, 2, 8, 15, 6])==[2, 15]
  assert min_max([1])==[1, 1]
  assert min_max([-1, -2, -3, -1])==[-3, -1]
  assert min_max([])==[]
  assert min_max([10, 10, 10])==[10, 10]
output: def min_max(arr):
    if not arr:
      return []
    min_val = min(arr)
    max_val = max(arr)
    return [min_val, max_val]