If a process happens in stages with $n_1, n_2, \ldots, n_k$ choices, the total number of outcomes is the product:

$$|\Omega| = \prod_{i=1}^{k} n_i$$

Given a list of per-stage counts, return the total number of outcomes.

solve([3, 4, 2])  ->  24     # 3 learning rates x 4 batch sizes x 2 optimizers