LeetCode 278. First Bad Version

题目：
You are a product manager and currently leading a team to develop a new product. Unfortunately, the latest version of your product fails the quality check. Since each version is developed based on the previous version, all the versions after a bad version are also bad.

Suppose you have n versions [1, 2, …, n] and you want to find out the first bad one, which causes all the following ones to be bad.

You are given an API bool isBadVersion(version) which will return whether version is bad. Implement a function to find the first bad version. You should minimize the number of calls to the API.

思路：
就是如果一个坏版本之后的所有版本都为坏版本，要求找出第一次出现坏版本的位置，也就是制造坏版本的那个原始坏版本。
利用二分查找，但是边界条件稍微有一点不一样，具体见代码注释。

代码：

// Forward declaration of isBadVersion API.bool isBadVersion(int version);class Solution {public:    int firstBadVersion(int n) {        int low=1;//初始化low为1，high为n        int high=n;        int mid=(high-low)/2+low;//mid=(high-low)/2+low，不使用mid=(high+low)/2是为了防止high+low溢出        while(low<high){//循环边界条件            if(isBadVersion(mid)){//如果当前位置为坏版本                high=mid;//那么high为mid(不要用mid-1)，要将mid也算进去                mid=(high-low)/2+low;//更新mid            }            else{//如果当前位置不是坏版本，也就是坏版本在之后                 low=mid+1;//这里low是mid+1                mid=(high-low)/2+low;//更新mid            }        }        return mid;//最终返回的mid即为第一次出现的坏版本    }};

程序输出： 0ms