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.

 1 /* The guess API is defined in the parent class GuessGame.
 2    @param num, your guess
 3    @return -1 if my number is lower, 1 if my number is higher, otherwise return 0
 4       int guess(int num); */
 5 
 6 public class Solution extends GuessGame {
 7     public int guessNumber(int n) {
 8         int l=1, r=n;
 9         while (l <= r) {
10             int m = l + (r-l)/2;
11             int guessRes = guess(m);
12             if (guessRes == 0) return m;
13             else if (guessRes == -1) r = m - 1;
14             else l = m + 1;
15         }
16         return Integer.MAX_VALUE;
17     }
18 }