Product of the Last K Numbers

Problem Design a data structure over a stream of integers supporting add(num) and getProduct(k) — the product of the last k numbers added. Zeros must be handled correctly.

Input / Output

• add(num): append num to the stream. getProduct(k): return the product of the last k added values.
• Output: the product for each getProduct call.

Constraints

• Up to 4·10^4 operations; getProduct must be O(1) (recomputing the window per query is the naive answer).
• Values may include zero.

Example

• add 3, add 0, add 2, add 5, add 4 → getProduct(2) = 20, getProduct(3) = 40, getProduct(4) = 0 (window includes the 0).