1352.js

/** ------------------------------------------------------------------------------
 * 
 * 1352. Product of the Last K Numbers
 * Topics: Prefix Sum
 * https://leetcode.com/problems/product-of-the-last-k-numbers/?envType=daily-question&envId=2025-02-14
 * 
 ------------------------------------------------------------------------------ */
var ProductOfNumbers = function () {
  this.prefix = [1]
}

/**
 * @param {number} num
 * @return {void}
 */
ProductOfNumbers.prototype.add = function (num) {
  if (num === 0) {
    this.prefix = [1]
  } else {
    this.prefix.push(this.prefix[this.prefix.length - 1] * num)
  }
}

/**
 * @param {number} k
 * @return {number}
 */
ProductOfNumbers.prototype.getProduct = function (k) {
  const len = this.prefix.length
  if (k >= len) {
    return 0
  }
  return this.prefix[len - 1] / this.prefix[len - 1 - k]
}

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