input: Write a function to sort a given array in ascending order using the bubble sort algorithm. The function should modify the input array in-place.
  
  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]
  
  arr = [3, 7, 4, 1]
  bubble_sort(arr)
  assert arr == [1, 3, 4, 7]
  
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]