First Bad Version

简单的二分模板就可以解决了，注意上下界

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

        return start if isBadVersion(start) else end