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 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.

Example:

Given n = 5, and version = 4 is the first bad version.


call isBadVersion(3) -> false
call isBadVersion(5) -> true
call isBadVersion(4) -> true

Then 4 is the first bad version.

Code

# 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
        """
        i , j = 1, n 
        while i <= j:
            mid = i + (j - i >> 1)
            if isBadVersion(mid):
                j = mid - 1

            else:
                i = mid + 1

        return i