input: Write a function to rearrange an array in descending order.
  assert rearrange_arr([1, 2, 3, 4, 5]) == [5, 4, 3, 2, 1]
  assert rearrange_arr([10, 1, 2, 9, 5]) == [10, 9, 5, 2, 1]
  assert rearrange_arr([3, 3, 2, 1, 4]) == [4, 3, 3, 2, 1]
output: def rearrange_arr(arr):
      return sorted(arr, reverse=True)