# 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.
```

## 题目大意：

我们来玩猜数字游戏。游戏规则如下：

我挑选一个1到n之间的数字。你来猜我选的是哪个数字。

每一次你猜错，我都会告诉你数字高了还是低了。

你可以调用一个预定义的API guess(int num)，返回3种结果 (-1, 1, 或 0)：

```
-1 : 我的数字更低
 1 : 我的数字更高
 0 : 恭喜你！猜对了！
```

测试用例如题目描述。

## 解题思路：

二分查找（Binary Search）

```
# The guess API is already defined for you.
# @param num, your guess
# @return -1 if my number is lower, 1 if my number is higher, otherwise return 0
# def guess(num):

class Solution(object):
    def guessNumber(self, n):
        """
        :type n: int
        :rtype: int
        """
        left, right = 0, n
        while left <= right:
            mid = (left + right)/2
            trial = guess(mid)
            if trial == -1:
                right = mid - 1
            elif trial == 1:
                left = mid + 1
            else:
                return mid
```
