guessNumber.cpp

public:
    int guessNumber(int n) {
        int l =1;
        int r = n;
        while (l <=r){
            
            int mid = l+(r-l)/2;
            int res = guess(mid);
            
            if (res==0) return mid;
            else if (res == -1) {
                r = mid - 1;    
            }
            else {
                l = mid + 1;
            }
        }
        return -1;
    }
};