While learning to write compilers, I would memorize small, but critical, programs like converting a char range, like [a-zA-Z_], in string format into a table or reporting an error if the range was invalid. At my peak, I could implement the function that did this in about 60 lines of Lua in about 3 minutes.
I haven't done exercises like that recently, but I found it helpful at the time.
20-30 years ago that was a role in competitive programming team - fast typer with knowledge of data structures, whose job was exactly that: very fast and bug less writing of them during competition
I came to a belief recently that memorization is way too underrated of a skill. Most of programmers, myself included believe that why you should memorize something if you can look it up, but... I'm not really sure by now.
Perhaps we rely too much on our ego that we can come up with everything on the fly where we should instead look into how other crafts did it in the past?
I haven't done exercises like that recently, but I found it helpful at the time.