C++ OOP Prefix Product解Leetcode 1352 Product of the Last K Numbers

C++ OOP Prefix Product解Leetcode 1352  Product of the Last K Numbers

Leetcode這題1352. Product of the Last K Numbers，是很好的OOP題目，除了談談class之外，還能練習一下prefix product的概念(與prefix sum類似但要小心0)

[C++解請進]

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Leetcode question 1352. Product of the Last K Numbers is a good OOP question. In addition to talking about class, you can also practice the concept of prefix product (similar to prefix sum but be careful with 0)

[codes on Leetcode]https://leetcode.com/problems/product-of-the-last-k-numbers/solutions/6419768/prefix-product-12ms-beats-91-95/

[Prefix Sum playlist]https://www.youtube.com/watch?v=1kA_aZHewmU&list=PLYRlUBnWnd5LkYN-5ptHDrtPXOuHm9uSq

class ProductOfNumbers {
public:
    vector product={1};
    int n=1;
    ProductOfNumbers(){
        product.reserve(40000);
    }
    
    void add(int num) {
        if (num==0) {
            product={1};
            n=1;
        }
        else{
            product.push_back(product[n++-1]*num);
        }
    }
    
    int getProduct(int k) {
        if (n<=k) return 0;
        return product[n-1]/product[n-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);
 */