#339 — Aug 31, 2026 by Evan Chen

Something I wrote in an email reply today, to a student asking about judging problem difficulty:

(begin quote)

While you can tell whether you have a correct solution without talking to others, I think you generally can't tell the difficulty of a problem without external contact, even if you solve it. Usually to make a judgment you need to at least know what alternate solutions exist, or whether you found the best possible solution, etc., and I don't see a way to do this without talking to other people.

However, during an exam, this is a completely academic debate for you. The only thing that matters is the problem difficulty for you personally. It is totally irrelevant to you how hard the problem is for anyone else and trying to think about that is just a distraction.

If the problem is easy for you, maybe because you've seen the right idea recently, or the problem just clicks, then it doesn't matter that it's hard for other contestants; go solve that one. Whereas if the problem is impossible for you, it doesn't matter that other contestants might solve it.

(end quote)