LeetCode278. 第一个错误的版本

调用题目给的API，二分查找第一个错误的版本。

// The API isBadVersion is defined for you.
// bool isBadVersion(int version);

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