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.

考察Binary Search

 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 left = 1, right = n;
 9        while (left + 1 < right) {
10            int mid = left + (right - left) / 2;
11            if (guess(mid) == 0) {
12                return mid;
13            } else if (guess(mid) == 1) {
14                left = mid;
15            } else {
16                right = mid;
17            }
18        }
19        if (guess(left) == 0) {
20            return left;
21        } else {
22            return right;
23        }
24     }
25 }