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

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