Formatted question description: https://leetcode.ca/all/1352.html

# 1352. Product of the Last K Numbers (Medium)

Implement the class ProductOfNumbers that supports two methods:

1. add(int num)

• Adds the number num to the back of the current list of numbers.

2. 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.

At any time, the product of any contiguous sequence of numbers will fit into a single 32-bit integer without overflowing.

Example:

Input
[[],,,,,,,,,,]

Output
[null,null,null,null,null,null,20,40,0,null,32]

Explanation
ProductOfNumbers productOfNumbers = new ProductOfNumbers();
productOfNumbers.getProduct(2); // return 20. The product of the last 2 numbers is 5 * 4 = 20
productOfNumbers.getProduct(3); // return 40. The product of the last 3 numbers is 2 * 5 * 4 = 40
productOfNumbers.getProduct(4); // return 0. The product of the last 4 numbers is 0 * 2 * 5 * 4 = 0
productOfNumbers.getProduct(2); // return 32. The product of the last 2 numbers is 4 * 8 = 32


Constraints:

• There will be at most 40000 operations considering both add and getProduct.
• 0 <= num <= 100
• 1 <= k <= 40000

Related Topics:
Array, Design

## Solution 1. Prefix Product

// OJ: https://leetcode.com/problems/product-of-the-last-k-numbers/
// Time: O(1) for all functions
// Space: O(N)
class ProductOfNumbers {
vector<int> v{1};
public:
ProductOfNumbers() {}