README.md

1352. Product of the Last K Numbers

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:
["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]
Explanation:
ProductOfNumbers 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 = 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.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:

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

Solutions (Rust)

1. Solution

struct ProductOfNumbers {
    products: Vec<i32>,
}


/** 
 * `&self` means the method takes an immutable reference.
 * If you need a mutable reference, change it to `&mut self` instead.
 */
impl ProductOfNumbers {

    fn new() -> Self {
        Self {
            products: vec![1],
        }
    }

    fn add(&mut self, num: i32) {
        match num {
            0 => self.products.truncate(1),
            _ => self.products.push(*self.products.last().unwrap() * num),
        }
    }

    fn get_product(&self, k: i32) -> i32 {
        let len = self.products.len();

        if k > len as i32 - 1 {
            return 0;
        }
        self.products[len - 1] / self.products[len - 1 - k as usize]
    }
}

/**
 * Your ProductOfNumbers object will be instantiated and called as such:
 * let obj = ProductOfNumbers::new();
 * obj.add(num);
 * let ret_2: i32 = obj.get_product(k);
 */