leetcode:278. First Bad Version

278. 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.

这个题目很简单,解决办法是不断的用中间值判断是不是bad version.由此二分,不断的缩小判断范围,直至逼近到答案,时间复杂度是 log n

这道题要注意的是:

用mid =(start+end)/2 算中间值有可能会导致int类型的overflow(对C /C++ ,Java).用Python 的时候虽然不会 overflow 但是当 start+end 大小超过 int 型最大值的时候Python 编译器会把它分成两个小于int型的数据分别计算,因此有可能超时,最好用 mid = start +(end-start)/2计算中间值.

下面是我的代码(python)

# 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
        """
        start = 1
        end = n
        while start < end:
            c_v = start +(end-start)>>1
            if isBadVersion(c_v) is True:
                end = c_v
            else :
                start = c_v+1
        return start