input: Write a function to sort an array in ascending order. If the array is empty, return the array as it is.
  def sort_ascending(array):
    if not array:
      return array
    return sorted(array)
  
  assert sort_ascending([10, 3, 9, 1, 15, 2])==[1, 2, 3, 9, 10, 15]
  assert sort_ascending([])==[]
output: def sort_ascending(array):
    if not array:
      return array
    return sorted(array)