374. Guess Number Higher or Lower

We are playing the Guess Game. The game is as follows:

我们来玩一个游戏，规则如下：

I pick a number from 1 to n. You have to guess which number I picked.

我从1到n之间选择一个数字，由你来猜我选了哪个数字。

Every time you guess wrong, I'll tell you whether the number is higher or lower.

在你每次猜错后，我会告诉你我选的数字比你猜的数字高还是低。

You call a pre-defined API guess(int num) which returns 3 possible results (-1, 1, or 0):

你可以用一个已经准备好的接口guess(int num)，它会返回3个可能的结果（-1,1或0）：

-1 : My number is lower　　　　//我的数字更小
 1 : My number is higher　　　//我的数字更大
 0 : Congrats! You got it!　　//猜中了

刚开始第一次提交采用了二分查找，不过显示超时了。

超时case: 2126753390

　　　　   1702766719

看讨论发现是溢出了，所以改了下程序。

// 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,high=n,g,r;
        while(low<=high){
            g=(low+high)/2;　　//改成g=low+(high-low)/2;
            r=guess(g);
            if(r==-1)high=g-1;
            else if(r==1)low=g+1;
            else return g;
        }
        return 0;
    }
};