First Bad Version

依然二分，转向条件，容易出问题的地方。

对于<=情况，截止区间是0；使用mid-1需要多进行一次查找通过left=mid+1修正区间；

对于<情况，截止区间是1；使用right=mid可以直接得到正确区间。

https://leetcode.com/problems/first-bad-version/

// Forward declaration of isBadVersion API.
bool isBadVersion(int version);

class Solution {
public:
    int firstBadVersion(int n) {
        int left = 1;
        int right = n;
        int mid ;
        while(left <= right) {
            mid = left + (right - left) / 2;
            if(isBadVersion(mid)) {
                right = mid - 1;
            } else {
                left = mid + 1;
            }
        }
        return left;
    }
};

// Forward declaration of isBadVersion API.
bool isBadVersion(int version);

class Solution {
public:
    int firstBadVersion(int n) {
        int left = 1;
        int right = n;
        int mid ;
        while(left < right) {
            mid = left + (right - left) / 2;
            if(isBadVersion(mid)) {
                right = mid;
            } else {
                left = mid + 1;
            }
        }
        return left;
    }
};