The whole array has p (4,4) = 24.

Note the cyclic arrangement of 1234, 234 1, 34 12, 4 123, and the obtained m values are the same.

According to this grouping, it can be divided into 6 groups with 24 ÷ 4 =, and each group has the same m value.

Note again that the positive sequence and the reverse sequence have the same value of m.

So b has three elements.

Let's think in a simpler way. This problem is equivalent to putting four beads of different colors into a bracelet. There are several ways to wear it.