leetcode 374. Guess Number Higher or Lower

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

class Solution {
public:
int guessNumber(int n) {
int low = 1,high = n;
while(low <= high){
int mid = (0LL+low+high)/2;
int y = guess(mid);
if(y == 0) return mid;
else if(y == 1)low = mid+1;
else high = mid - 1;
}
return low;

}
};