374. Guess Number Higher or Lower

/** 
 * Forward declaration of guess API.
 * @param  num   your guess
 * @return 	     -1 if num is higher than the picked number
 *			      1 if num is lower than the picked number
 *               otherwise return 0
 * int guess(int num);
 */

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

        }

        return {};
    }
};