code: def pancake_sort(arr):
      len_arr = len(arr)
      if len_arr <= 1:
          return arr
      for cur in range(len(arr), 1, -1):
          index_max = arr.index(max(arr[0:cur]))
          if index_max+1 != cur:
              if index_max != 0:
                  arr[:index_max+1] = reversed(arr[:index_max+1])
              arr[:cur] = reversed(arr[:cur])
      return arr