資料結構與演算法

(4 points) Let $S$ be a stack containing $n+1$ coefficients $a_0, a_1, \dots, a_n$, where $n \ge 1$, $a_n$ is at the top of the stack, and $a_0$ is at the bottom. The following algorithm computes $f(x) = \sum_{i=0}^{n} a_i x^i$. Identify the missing expression $\square$ in the pseudocode.

POLY(S, x):
1   while S.size ≥ 2
2       u = S.pop()
3       v = S.pop()
4       S.push(□)
5   return S.pop()