Slow performance compared to legacy

[monkeygroover]

So... I was trying Advent of Code and solved day 6 but only in legacy:

https://tio.run/##TVExTgNBDHwORRYp47VP0CPavCFIUR6QEkUKBT0foKCLRIn4QLagy5cud/Z4D1mrPXtn7PHc2rYv2I3jXbl8vV5/rr/749P@8XDf3teX7/YmNjy3U/sY2vnw0M6r4e/zuBnHWlCsqIeV6jemI2V@qVOIH5sy@OucqR84Y87FEeYM9dvIABnVI@cYexuzwIpjlVVx1nznS7BAjakssMpJgQiksWJ9lnh/eE9QTaVOcO/UAvoR/oRedJ/ASnzZP2Zso/RkQaZXSj@Fe2qvms@Vrjr3razmBrlF5VTlNFAt2DXDuI3170UfiNTeOx2U7iP4vwOdfRZflB2NrKnfDQ

however this is too slow in the elixir version, not sure why yet, stack recursion perhaps?

https://tio.run/##TVExbsMwDHxOhqpASZFGuwdZ@4YEKIxOHTwWAZKhez7QoZuBjEU@YA3Z/CXXJo9yQQgyqTvyeP7o9of3t2napOHnc/wdb@1x2750j@XrabiWM2uzK6dyaUrfPZf@obl/H1@nKSdKmsRCU7ab5sNpeclzsB2dM7LXJRM7ZIwlZ0OoMcRuBYPAyBYxR9FbkTmWDSuosrGWO16cRdAYyhwrmOQIRyoqWmex9SfrSVCToZOwd2gh@OH@uF6qPhEq/qX/mL6NwJMVGV4J/GTsKbWqNper6tg3oxobxBYZUwXTCGoJXSMU22j9XvURkFJ7h4NcfST8b0dHn9UXQUcFa@73Bw

[monkeygroover]

This appears to be because rotate becomes more and more inefficient if done repeatedly on a stream, If do this:

    def rotate(value, shift) when shift == 0, do: value
    def rotate(value, shift) when not Functions.is_iterable(value), do: Enum.join(rotate(String.graphemes(to_string(value)), shift), "")
    def rotate(value, shift) when shift > 0 do
        case Enum.count value do
            0 -> []
            x -> 
                shift = rem(shift, x)
                Stream.concat(value |> Stream.drop(shift), value |> Stream.take(shift)) |> Enum.to_list
        end
    end
    def rotate(value, shift) when shift < 0 do
        case Enum.count value do
            0 -> []
            x ->
                shift = rem(shift, x)
                Stream.concat(value |> Stream.take(shift), value |> Stream.drop(shift)) |> Enum.to_list
        end
    end

It's very fast again.

Not sure if there are any downsides, going to run the tests. But using rotate on large streams probably isn't a good idea anyway.

[Adriandmen]

Yeah, there were a couple of downsides after rewriting this from Python to Elixir. Performance was indeed one of the biggest regressions.

Both versions have bugs, this one is just less buggy hahaha. Ideally I would rewrite it again in Scala or Java (or some other strongly typed language), but I can barely find the time for doing so unfortunately.

[monkeygroover]

Yeah, Rust may work too (but no GC, so lots to learn)

I actually did this to get some clues: https://github.com/monkeygroover/05AB1E/tree/flame hacky but helped!

[Adriandmen]

Oohh, that is clever!

I will definitely have to check that out, thanks for sharing! :)