Yes. I wonder why they didn't just roll back the attacker's moves? It seems like the problem is one of those NP-hard type situations, where the solution is very

Yes. I wonder why they didn't just roll back the attacker's moves? It seems like the problem is one of those NP-hard type situations, where the solution is very complex (hence crowdsourcing as a brute-force solution, rather than anything algorithmic) but checking a proposed solution is tractable. You might be able to validate a move (or perhaps a block of moves) and either keep or reject.