Guess 16 Nov Number Higher or Lower

class Solution {
public:
    int guessNumber(int n) {
        int s = 1;
        int e = n;
        int mid = s + (e-s)/2;
        while(s <= e){
            if(guess(mid) == 0){
                return mid;
            }
            else if(guess(mid) == 1){
                s = mid +1;
            }
            else if(guess(mid) == -1){
                e = mid -1;
            }
            mid = s + (e-s)/2;
        }
        return -1;
    }
};