Guess Number Game

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):

您在真实的面试中是否遇到过这个题？ 

Yes

样例

n = 10, I pick 4 (but you don't know)

Return 4. Correct !

   public int guessNumber(int n) {//        System.out.println(K);        int l = 1, r = n;        int m;        while (l <= r) {            m = l + (r - l) / 2; //防止溢出            int k = guess(m);            if (k == 0) return m;            else if (k == -1) r = m - 1;            else l = m + 1;        }        return 0;    }