1518. Water Bottles

TC = O(1)
class Solution {
public:
    int numWaterBottles(int numBottles, int numExchange) {
        return (numBottles + (numBottles-1 )/ (numExchange -1));
    }
};


TC = O(n)
class Solution {
public:
    int numWaterBottles(int numBottles, int numExchange) {
         int ans = numBottles;
        while( numBottles >= numExchange ){
             int FullBottle = numBottles/numExchange;
              ans += FullBottle;
             int EmptyBottle   = numBottles % numExchange  ;
             numBottles = EmptyBottle + FullBottle;
        }
        return ans;
    }
};