Leetcode: 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.

Binary Search

Here "My" means the number which is given for you to guess not the number you put into guess(int num).

/* The guess API is defined in the parent class GuessGame.
   @param num, your guess
   @return -1 if my number is lower, 1 if my number is higher, otherwise return 0
      int guess(int num); */

public class Solution extends GuessGame {
    public int guessNumber(int n) {
        int l=1, r=n;
        while (l <= r) {
            int m = l + (r-l)/2;
            int guessRes = guess(m);
            if (guessRes == 0) return m;
            else if (guessRes == -1) r = m - 1;
            else l = m + 1;
        }
        return Integer.MAX_VALUE;
    }
}