input: Write a python function to reverse an array in place.
  assert reverse_array([1, 2, 3, 4]) == [4, 3, 2, 1]
  assert reverse_array([10, 20, 30, 40, 50]) == [50, 40, 30, 20, 10]
  assert reverse_array([7, 8, 9]) == [9, 8, 7]
output: def reverse_array(arr):
      left, right = 0, len(arr) - 1
      while left < right:
          arr[left], arr[right] = arr[right], arr[left]
          left += 1
          right -= 1
      return arr