LeetCode-Guess_Number_Higher_or_Lower

题目：

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.

翻译：

我们在玩一个猜的游戏，游戏是如下这样的：

我从 1 到 n 中选择一个数字，你需要猜出我选择时哪一个数字。

每一次你猜错后，我都会告诉你猜的数字是高了还是低了。

你调用一个预定义的API guess(int num) 返回3个可能的结果（-1, 1,或 0）：

-1 : 我的数字要低一些
 1 : 我的数字要高一些
 0 : 祝贺你，你找到了！

例子：

n = 10, 我选择 6.

返回 6.

思路：

这道题就是一道二分查找的问题。之前也写过类似的题目。具体见代码。

C++代码（Visual Studio 2017）：

// Forward declaration of guess API.
// @param num, your guess
// @return -1 if my number is lower, 1 if my number is higher, otherwise return 0
int guess(int num);

class Solution {
public:
	int guessNumber(int n) {
		int low = 1;
		int high = n;
		while (low <= high) {
			int mid = low + (high - low) / 2;
			if (guess(mid) == -1) {
				high = mid - 1;
			}
			if (guess(mid) == 1) {
				low = mid + 1;
			}
			if (guess(mid) == 0)
				return mid;
		}

	}
};