Water Bottles Python Solution with Tests

lcpy gen -n 1518   # by problem number
lcpy gen -s water_bottles   # by problem name

Input: numBottles = 9, numExchange = 3
Output: 13
Explanation: You can exchange 3 empty bottles to get 1 full water bottle.
Number of water bottles you can drink: 9 + 3 + 1 = 13.

Input: numBottles = 15, numExchange = 4
Output: 19
Explanation: You can exchange 4 empty bottles to get 1 full water bottle.
Number of water bottles you can drink: 15 + 3 + 1 = 19.

class Solution:
    # Time: O(log numBottles)
    # Space: O(1)
    def num_water_bottles(self, num_bottles: int, num_exchange: int) -> int:
        drunk = num_bottles
        empty = num_bottles
        while empty >= num_exchange:
            full, empty = divmod(empty, num_exchange)
            drunk += full
            empty += full
        return drunk