边工作边刷题：70天一遍leetcode: day 58-1

First Bad Version

要点：本质上就是>=的bounded binary search，因为在某一点之后都是bad version，目标是找到起点。
错误点：

• =并不是(low+high+1)/2，low=mid的情况才是，也就是<=或者<（策略：面试中还是只提low+(high-low)/2，如果面试官有考点，那一定是会提示，然后再顺水推舟）

# The isBadVersion API is already defined for you.
# @param version, an integer
# @return a bool
# def isBadVersion(version):

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