【单选题】Given that the pushing sequence of a stack is {1, 2, ⋯ , n} and popping sequence is {p1, p2, ⋯ , pn}. If p1 = n, how many different possible popping sequences can we obtain?
【单选题】Given that the pushing sequence of a stack is {1, 2, ⋯ , n} and popping sequence is {p1, p2, ⋯ , pn}. If p2 = n, how many different possible popping sequences can we obtain?