You are a product manager and currently leading a team to develop a new product. Unfortunately, the latest version of your product fails the quality check. Since each version is developed based on the previous version, all the versions after a bad version are also bad.

Suppose you havenversions[1, 2, ..., n]and you want to find out the first bad one, which causes all the following ones to be bad.

You are given an APIbool isBadVersion(version)which will return whetherversionis bad. Implement a function to find the first bad version. You should minimize the number of calls to the API.

二分查找， 但是一直有个问题调不过，  mid如果好的， 那么start  = mid +1 而不是start = mid， 否则死循环出不来了。=。=！！！ 人生处处是陷阱啊。