First Bad Version

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 have n versions [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 API bool isBadVersion(version) which will return whether version is bad. Implement a function to find the first bad version. You should minimize the number of calls to the API.

简单题，还是来自师兄的提交，其实实质时寻找第一个为True值的位置，所以很简单，代码如下：

class Solution(object):
    def firstBadVersion(self, n):
        """
        :type n: int
        :rtype: int
        """
        low = 1
        high = n
        while low<= high:
            mid = low + (high-low)/2
            if isBadVersion(mid):
                high = mid-1
            else:
                low = mid+1
        return low

另外一种会越界然后返回的代码为，运行时间要短一些：

class Solution(object):
    def firstBadVersion(self, n):
        """
        :type n: int
        :rtype: int
        """
        low = 1
        high = n
        while low<= high:
            mid = low + (high-low)/2
            if isBadVersion(mid):
                high = mid-1
            else:
                low = mid+1
        return low