[scottlamb]

> For the very specific dataset used in the challenge, the hash function could be radically simplified, to just a single multiply and rotate left.

That's just a custom hash function, though; couldn't you do that with the standard std::collections::HashMap?

[haxen]

I didn't bother to try, so not sure. There would probably be some challenges and I don't see how I'd accomplish it without some branch instruction in the custom hasher.