>>> for i in range(n):

...     _arr = [i * 5 + a for a in range(n)]

...     if (i + 1) % 2 == 0:

...             _arr = list(reversed(_arr))

...     print(_arr)

...

[0, 1, 2, 3, 4]

[9, 8, 7, 6, 5]

[10, 11, 12, 13, 14]

[19, 18, 17, 16, 15]

[20, 21, 22, 23, 24]