提供一个guess(int num)的api，针对猜测的数字，返回三个数值。0，-1,1

• 0;猜中返回num
• -1：比猜测的数值小
• 1：比猜测的数值大

n = 10, I pick 6.

Return 6.

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!

n = 10, I pick 6.

Return 6.

• 明显是二分法的应用，关于二分法，看我之前的一片博客，讲的比较详细，链接如下：
  Java语言实现二分法

/* 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 L = 1,R = n;
        while(L <= R){
            int mid = L + ((R - L) >> 1);
            int res = guess(mid);
            if(res == 0) return mid;
            else if(res == 1)  L = mid + 1;
            else R = mid - 1;
        }
        return L;
    }
}