b_idx = np.random.randint(0, 9, 90)

>>> b_idx

array([0, 1, 5, 4, 7, 2, 7, 0, 0, 4, 2, 2, 3, 5, 6, 4, 7, 0, 3, 2, 7, 3,

       8, 5, 4, 3, 1, 8, 6, 6, 5, 5, 3, 2, 2, 2, 0, 4, 8, 1, 5, 3, 2, 6,

       2, 3, 3, 3, 0, 4, 5, 1, 4, 0, 6, 7, 6, 3, 4, 7, 8, 5, 8, 6, 7, 6,

       6, 6, 3, 1, 6, 1, 4, 6, 4, 7, 4, 8, 6, 6, 7, 7, 1, 0, 6, 0, 4, 1,

       5, 2])