input: Write a function to sort a given array in ascending order using bubble sort. The function should modify the input array in place and return None.
  def bubble_sort(arr):
      n = len(arr)
      for i in range(n-1):
          for j in range(0, n-i-1):
              if arr[j] > arr[j+1]:
                  arr[j], arr[j+1] = arr[j+1], arr[j]
  
  assert bubble_sort([3,7,4,1])==None
  assert bubble_sort([])==None
  assert bubble_sort([5,4,3,2,1])==None
  assert bubble_sort([1,2,3,4,5])==None
  assert bubble_sort([3,7,4,1])==None
output: def bubble_sort(arr):
      n = len(arr)
      for i in range(n-1):
          for j in range(0, n-i-1):
              if arr[j] > arr[j+1]:
                  arr[j], arr[j+1] = arr[j+1], arr[j]