278. First Bad Version

！！！题目链接！！！

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

class Solution {
public:
    int firstBadVersion(int n) {
        long rb = n;
        long lb = 1;
        long mid = 0;

        while(lb != rb){
            mid = (rb+lb) / 2;
            if(!isBadVersion(mid)){
                lb = mid+1;
            }else{
                rb = mid;
            }
        }
        return rb;
    }
};