One of my favorite anecdotes, that I read on hn and unfortunately didn't save, is that a constant space algorithm for loop checking in a linked list was an open

One of my favorite anecdotes, that I read on hn and unfortunately didn't save, is that a constant space algorithm for loop checking in a linked list was an open question for a long time. The rabbit and hare algorithm was novel enough that it was first published by Knuth in 1969. So if you're asked that question in an interview, it's only checking if you've heard the answer. Because you almost certainly aren't going to come up with it on the spot. That said, if you want to work at goog/fb/amazon/et al, you have to study, and that's a common dp problem. Put in your 100 hours of studying and you'll do fine. And before you grump at me, that's not an endorsement of this (I think it's quite silly), but we all know the deal. So stop whining and study before your interview, or don't bother interviewing with the well known list of companies that love algorithm bingo.