Guess Number Higher or Lower

We are playing the Guess Game. The game is as follows:

I pick a number from 1 to n. You have to guess which number I picked.

Every time you guess wrong, I'll tell you whether the number is higher or lower.

You call a pre-defined API guess(int num) which returns 3 possible results (-1, 1, or 0):

-1 : My number is lower 1 : My number is higher 0 : Congrats! You got it! Example: n = 10, I pick 6. Return 6.

Solution: Binary Search

int guessNumber(int n) {
    int left = 1, right = n, mid = 0;
    while (left <= right) {
        mid = left + (right - left)/2;
        int res = guess(mid);
        if (res == 0) return mid;
        else if (res == -1) right = mid-1;
        else left = mid+1;
    }

    return left;
}