278. First Bad Version

https://leetcode.com/problems/first-bad-version/description/
    int firstBadVersion(int n) {
        int lo = 1, hi = n;
        while(lo<hi){
            int mid = lo +(hi - lo)/2;
            if(isBadVersion(mid)) hi = mid;
            else lo = mid + 1;
        }
        return lo;
    }