278.第一个错误的版本——记录（C++）

class Solution {
public:
    int firstBadVersion(int n) {
        int l=1;
        int r=n;
        int mid=1/2+n/2;
        while(r>=l)
        {
            if(!isBadVersion(mid)&&isBadVersion(mid+1))
            {
                mid= mid+1;
                break;
            }
            else if(isBadVersion(mid)&&!isBadVersion(mid-1))
            {
                 break;
            }
            else if(isBadVersion(mid))
            {
                r=mid-1;
                mid=r/2+l/2;
            }
            else if(!isBadVersion(mid))
            {
                   l=mid+1;
                   mid=r/2+l/2;
            }
        }
        return mid;
    }
};

加油！