卖萌的弱渣

I am stupid, I am hungry.

First Bad Version

First Bad Version

The code base version is an integer start from 1 to n. One day, someone committed a bad version in the code case, so it caused this version and the following versions are all failed in the unit tests. Find the first bad version.

You can call isBadVersion to help you determine which version is the first bad one. The details interface can be found in the code’s annotation part.

Example

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Given n = 5:

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

Here we are 100% sure that the 4th version is the first bad version.

Note

Please read the annotation in code area to get the correct way to call isBadVersion in different language. For example, Java is SVNRepo.isBadVersion(v)

Challenge

You should call isBadVersion as few as possible.

Solution

  • Time: O(log n)
  • Binary search [1,n] find the smallest value x (isBadVersion(x) == True)
(First-Bad-Version.py) download
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#classSVNRepo:                                                              
#    @classmethod
#    def isBadVersion(cls, id)
#        # Run unit tests to check whether verison `id` is a bad version
#        # return true if unit tests passed else false.
# You can useSVNRepo.isBadVersion(10) to check whether version 10 is a 
# bad version.

class Solution:
    """
     @param n: An integers.
     @return: An integer which is the first bad version.
    """
    def findFirstBadVersion(self, n):
        # your code here
        front = 1
        end = n
        result = sys.maxint
        while front <= end:
            mid = (front+end)/2
            if SVNRepo.isBadVersion(mid) == True:
                end = mid-1
                if result > mid:
                    result = mid
            else:
                front = mid + 1
        return result