I can't tell during my limited time in an interview if a developer has that knowledge because they crammed (and therefore will forget quickly on the job) or if

I can't tell during my limited time in an interview if a developer has that knowledge because they crammed (and therefore will forget quickly on the job) or if they actually study and understand this stuff. I can tell during my limited time in an interview if a developer is capable of making logical deductions and not flail when exposed to a problem they may not have seen before. And, better yet, if they do study algos for fun, this will become apparent!