1352. Product of the Last K Numbers

Design an algorithm that accepts a stream of integers and retrieves the product of the last k integers of the stream.

Implement the ProductOfNumbers class:

• ProductOfNumbers() Initializes the object with an empty stream.
• void add(int num) Appends the integer num to the stream.
• int getProduct(int k) Returns the product of the last k numbers in the current list. You can assume that always the current list has at least k numbers.

The test cases are generated so that, at any time, the product of any contiguous sequence of numbers will fit into a single 32-bit integer without overflowing.

class ProductOfNumbers {
    long long zero = INT_MAX;
    vector<long long> prefixProduct {1ll};
public:
    ProductOfNumbers() {}

    void add(int num) {
        if(!num) {
            prefixProduct.clear();
            prefixProduct.push_back(1ll);
            zero = 1;
        } else {
            prefixProduct.push_back(num * prefixProduct.back());
            zero++;
        }
    }

    int getProduct(int k) {
        if(k >= zero) return 0;
        return prefixProduct.back() / prefixProduct[prefixProduct.size() - k - 1];
    }
};

/**
 * Your ProductOfNumbers object will be instantiated and called as such:
 * ProductOfNumbers* obj = new ProductOfNumbers();
 * obj->add(num);
 * int param_2 = obj->getProduct(k);
 */