Site Moved

I’ve moved this blog to a self-hosted site. It’s quite a bit slower, unfortunately, but it gives me more control over the site, so I can do things like embedding code snippets and latex.

So if you want to follow along, change your shortcuts and head on over to:

Site Moved

Anonymous Extensible Identifiers (AXID)

It seems like every organization has their own arbitrary way of assigning numerical identifiers to people. You have a driver’s license number, a social security number, a tax ID, an employee ID, a voter ID, and on and on. Wouldn’t it be nice if everyone just had one single ID? And wouldn’t it be nice if you didn’t have to look this ID up in some kind of database? What if you could figure it out just from your knowledge of a person, even incomplete knowledge? But at the same time, a person’s identifier doesn’t actually reveal any information about them?

Ok, so privacy experts will probably warn about using a common ID for everything, but let’s just ignore them and think about how this could work.

Continue reading “Anonymous Extensible Identifiers (AXID)”

Anonymous Extensible Identifiers (AXID)

Battery Testing Brainteaser

Our team has recently started working on some brain teasers to sharpen our minds, expose us to new ideas, and keep up our fun factor.

This is our first one:

You are camping with your friends. You have a flashlight for any emergency and have brought 8 batteries along with you. Your brother calls to tell you that four of those batteries are already dead.
Your flashlight requires two working batteries to run. What is the least number of pairs you will need to test to guarantee that you can get the flashlight on?

To clarify, we’re counting the time when you actually load the working pair into the flashlight as a test. So even if you’ve done N tests and now you know for a fact that a certain pair is working, the answer is still N+1 if that working pair isn’t already guaranteed to be in the flashlight.

And “guaranteed” is key. Obviously, it may be the case that the first pair of batteries you test works. That doesn’t mean the answer is one, because in other cases you won’t be so lucky. You need to prove that there is a strategy you can use so that you always find a working pair of batteries within N tries, and furthermore that there is no strategy that will work with fewer than N tries.

Spoiler: Solution and Proof

So below is a solution to this brain teaser. It’s a really interesting problem, so [blah blah blah] ruin the funĀ [blah blah blah].

Continue reading “Battery Testing Brainteaser”

Battery Testing Brainteaser