Product of the Last K Numbers

Keep only the current zero-free segment

Maintain prefix = [1]. For add(x), if x == 0, reset it to [1]; otherwise append prefix.back() * x. For getProduct(k), if k >= prefix.length, a zero lies in the requested suffix, so return zero. Otherwise return prefix.back() / prefix[prefix.length - 1 - k]. The invariant is that entries represent cumulative products since the most recent zero, so division cancels exactly the earlier part of that segment. Each add and query is O(1) time; storage is O(n) between resets. Test zero immediately before a query, k = 1, several zeros, and products that require a wider numeric type. Do not retain one global prefix product because zero makes later division impossible.