278.第一个版本错误

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

public int firstBadVersion(int n) {
        int left=0,right=n,mid;
        while (left<right){
            mid = ((right-left)>>1)+left;
            if (isBadVersion(mid)){
                right = mid;
            }else {
                left = mid + 1;
            }
        }
        return left;
    }