main.cpp

// Source: https://leetcode.com/problems/water-bottles
// Title: Water Bottles
// Difficulty: Easy
// Author: Mu Yang <http://muyang.pro>

////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
// There are `numBottles` water bottles that are initially full of water. You can exchange `numExchange` empty water bottles from the market with one full water bottle.
//
// The operation of drinking a full water bottle turns it into an empty bottle.
//
// Given the two integers `numBottles` and `numExchange`, return the **maximum** number of water bottles you can drink.
//
// **Example 1:**
// https://assets.leetcode.com/uploads/2020/07/01/sample_1_1875.png
//
// ```
// 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.
// ```
//
// **Example 2:**
// https://assets.leetcode.com/uploads/2020/07/01/sample_2_1875.png
//
// ```
// 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.
// ```
//
// **Constraints:**
//
// - `1 <= numBottles <= 100`
// - `2 <= numExchange <= 100`
//
////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////

using namespace std;

class Solution {
 public:
  int numWaterBottles(int numBottles, int numExchange) {
    auto ans = numBottles;
    while (numBottles >= numExchange) {
      auto newBottles = numBottles / numExchange;
      ans += newBottles;
      numBottles -= newBottles * numExchange;
      numBottles += newBottles;
    }
    return ans;
  }
};