I can never remember what they are, though. To avoid this problem, I think I wrote them down on a post-it, but I had too many post-its on my desk so I got rid of them all, and now I can't remember.

The two most difficult ones are naming things, cache invalidation, and off-by-one errors. HTH. ;)

I prefer the ordered version.

three most difficult things in CS:

2) Naming Things

1) Cache Invalidation

4) off by one errors

3) Concurrency

Another version, about distributed systems:

There are only two hard problems in distributed systems:

2. Exactly-once delivery

1. Guaranteed order of messages

2. Exactly-once delivery

two most difficult things in CS:

0) naming things

1) cache invalidation

42) asynchronous callbacks

2) off by one errors

They are likely making a joke about caching the answer

What does HTH mean?

"Hope this helps" (sometimes used sarcastically)

Hope That Help, HTH.

"Hope this helps"

I see it with HAND "have a nice day" too

I've always read it as "Happy To Help".

I see that's wrong, but ignorance has made the internet seem just that little bit warmer all these years!

I think it could probably mean "Happy to help" if said in response to a thanks of some sort. Saying it before someone has said thanks is a bit presumptuous. :-)

this reminds me I was dumpster diving at a place with lots of post-it notes and there was one that said 2HCS => whatchamacallit, CI!

what that you?

on edit: I'm going to let that 'what that you' stand because one of the hardest things about HN posts is grammatical correctitude.

> wrote them down on a post-it

You write it on local media and kept it on-premises?

Cloud is the new thing, I hear.

The Post-it was but a cache.

I would consider the Post-it as persistent storage or the backup. Your memory would be the cache :D