You don't need to remember the details of a specific problem. Almost all the problems I've encountered interviewing for FAANGs were not found on such sites. You

You don't need to remember the details of a specific problem. Almost all the problems I've encountered interviewing for FAANGs were not found on such sites. You do need to remember classes of problems - graph traversal, tree traversal, dynamic programming, etc etc. But you should expect problems you've never seen before.