Contest 176 - LeetCode 1352. Product of the Last K Numbers

class ProductOfNumbers {
public:
    long long int a[50005];
    long long int s[50005];
    int len;
    int last;
    ProductOfNumbers() {
        len=0;
        s[0]=1;
        last=-1;
    }
    
    void add(int num) {
        
        a[len++]=num;
        if(num==0)
        {
            last = len-1;
            s[last+1]=1;
        }
        else
            s[len]=s[len-1]*num;
    }
    
    int getProduct(int k) {
        
        if( last ==-1 ||len-k > last)
            return s[len]/s[len-k];
        else
            return 0;
        
    }
};

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