When will this problem be posted on the open challenges on the main part of the website?

I'm looking for a solution written in C++, couldn't find one so far. If you have one, could you please share it with me?

How is the hash in the editorial calculated?

What do you mean by non-isomorphic trees? Isomorphism is defined on two trees. Do you want the size of the set of trees for which no pair of trees are isomorphic?