LeetCode 1352. 最后 K 个数的乘积

https://leetcode-cn.com/problems/product-of-the-last-k-numbers/

维护一个前缀积， 要求最后连续几个数的乘积只需后面的前缀积除以之前的前缀积。

注意0的情况，遇到0就清空前缀积。

class ProductOfNumbers {
public:
    vector prefix_product;

    ProductOfNumbers() {
    }
    
    void add(int num) {
        if(num==0){
            prefix_product.clear();
        }
        else{
            if(prefix_product.size()==0){
                prefix_product.push_back(num);
            }
            else
                prefix_product.push_back(prefix_product[prefix_product.size()-1]*num);
                printf("%d\n",prefix_product[prefix_product.size()-1]);
                
        }
       
    }
    
    int getProduct(int k) {
        
        if(k>prefix_product.size()){
            return 0;
        }
        if(k==prefix_product.size())
            return prefix_product[prefix_product.size()-1];
        return prefix_product[prefix_product.size()-1]/prefix_product[prefix_product.size()-1-k];
        
    }
};

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