Product of the Last K Numbers

Problem statement

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.

Example:

Input["ProductOfNumbers","add","add","add","add","add","getProduct","getProduct","getProduct","add","getProduct"][[],[3],[0],[2],[5],[4],[2],[3],[4],[8],[2]]Output[null,null,null,null,null,null,20,40,0,null,32]ExplanationProductOfNumbers productOfNumbers = new ProductOfNumbers();productOfNumbers.add(3);        // [3]productOfNumbers.add(0);        // [3,0]productOfNumbers.add(2);        // [3,0,2]productOfNumbers.add(5);        // [3,0,2,5]productOfNumbers.add(4);        // [3,0,2,5,4]productOfNumbers.getProduct(2); // return 20. The product of the last 2 numbers is 5 * 4 = 20productOfNumbers.getProduct(3); // return 40. The product of the last 3 numbers is 2 * 5 * 4 = 40productOfNumbers.getProduct(4); // return 0. The product of the last 4 numbers is 0 * 2 * 5 * 4 = 0productOfNumbers.add(8);        // [3,0,2,5,4,8]productOfNumbers.getProduct(2); // return 32. The product of the last 2 numbers is 4 * 8 = 32 

Constraints:

• 0 <= num <= 100
• 1 <= k <= 4 * 104
• At most 4 * 104 calls will be made to add and getProduct.
• The product of the stream at any point in time will fit in a 32-bit integer.

My solution

var ProductOfNumbers = function() {
    this.list = []
};

/** 
 * @param {number} num
 * @return {void}
 */
ProductOfNumbers.prototype.add = function(num) {
    this.list.push(num)
};

/** 
 * @param {number} k
 * @return {number}
 */
ProductOfNumbers.prototype.getProduct = function(k) {
    return this.list.slice(k * -1).reduce((acc, curr) => {
        return acc *= curr
    }, 1)
};

/** 
 * Your ProductOfNumbers object will be instantiated and called as such:
 * var obj = new ProductOfNumbers()
 * obj.add(num)
 * var param_2 = obj.getProduct(k)
 */