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] 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:
0 <= num <= 1001 <= k <= 4 * 1044 * 104 calls will be made to add and getProduct.Follow-up: Can you implement both
GetProduct and Add to work in O(1) time complexity instead of O(k) time complexity?
class ProductOfNumbers {
List<Integer> stream;
int cumulativePdt = 1, lastZeroIdx = -1;
public ProductOfNumbers() {
stream = new ArrayList<>();
}
public void add(int num) {
if (num == 0) {
lastZeroIdx = stream.size();
stream.add(cumulativePdt = 1);
} else
stream.add(cumulativePdt *= num);
}
public int getProduct(int k) {
return lastZeroIdx > stream.size() - 1 - k ? 0
: stream.get(stream.size() - 1) / stream.get(stream.size() - 1 - k);
}
}
/**
* Your ProductOfNumbers object will be instantiated and called as such:
* ProductOfNumbers obj = new ProductOfNumbers();
* obj.add(num);
* int param_2 = obj.getProduct(k);
*/