Experienced candidates shouldn't have to spend any time preparing for the technical portion of an interview - if they have to study something new to "pass" the interview, how does that reflect on their past or current abilities? All it does is show that they have time (or made time) to study for the interview. So either they are company megafan (which would be a good thing for the company) or more likely, they are after they money the company pays - so they aren't going to be the best employee.

No. Don't make candidates practice an otherwise nearly useless skill they will most likely never use on the job, when they can just look this algorithm up on the internet if they need it.