## Description

https://leetcode.com/problems/water-bottles/

Given `numBottles`

full water bottles, you can exchange `numExchange`

empty water bottles for one full water bottle.

The operation of drinking a full water bottle turns it into an empty bottle.

Return the **maximum** number of water bottles you can drink.

**Example 1:**

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

**Example 2:**

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

**Example 3:**

Input:numBottles = 5, numExchange = 5Output:6

**Example 4:**

Input:numBottles = 2, numExchange = 3Output:2

**Constraints:**

`1 <= numBottles <= 100`

`2 <= numExchange <= 100`

## Explanation

The key idea is to simulate the process, find out what are the steps in one iteration and what’s the condition to loop the iteration. Base on the example picture, we can consider 1. drinking bottles to empty bottles 2. exchange empty bottles for new bottles as steps in one iteration. Then when bottles + empty bottles are greater than the minimum exchange number, we loop the process.

## Python Solution

```
class Solution:
def numWaterBottles(self, numBottles: int, numExchange: int) -> int:
count = 0
empty_bottles = 0
while numBottles + empty_bottles >= numExchange:
count += numBottles
empty_bottles += numBottles
numBottles = empty_bottles // numExchange
empty_bottles = empty_bottles % numExchange
count += numBottles
return count
```

- Time Complexity: O(N).
- Space Complexity: O(1).