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 APIguess(int num)which returns 3 possible results (-1,1, or0):

-1 : My number is lower
 1 : My number is higher
 0 : Congrats! You got it!

Example:

n = 10, I pick 6.

Return 6.

Solution

/* 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 start = 0;
        int end = n;
        while (start <= end) {
            int mid = start + ((end - start) / 2);
            int result = guess(mid);
            if (result == 1) {
                start = mid + 1;
            } else  if (result == -1) {
                end = mid - 1;
            } else {
                return mid;
            }
        }
        return -1;
    }
}