Here is my natural (without any extra effort thinking about speed) F# solution: (for calibration I have the C++, unchanged, times) | 217 | 255 | 206 | 0.5 s

Here is my natural (without any extra effort thinking about speed) F# solution: (for calibration I have the C++, unchanged, times) | 217 | 255 | 206 | 0.5 s (C++ 1.6s) | 317 | 355 | 306 | 1 s (C++ 4.8s) | 617 | 655 | 606 | 3.5 s (C++ 35s) | 917 | 955 | 906 | 10s (C++ 117.5) code: let actions = [|[|-1; -1; 1|]; [|-1;1;-1|]; [|1; -1;-1|]|] let stable [| g ; w; l|] = (g = 0 && (w = 0 || l = 0)) || (w = 0 && l = 0) let isSound = function | [| x ; _; _|] | [|_; x; _|] | [|_; _; x|] when x < 0 -> false | _ -> true let stateChange state = Array.map (Array.map2 (+) state) actions let deduplicate sequence = sequence |> Seq.groupBy hash |> Seq.map (snd >> Seq.head) let forest start = let rec search curforest = let nextforest = Array.collect stateChange curforest |> Array.filter isSound |> deduplicate |> Seq.toArray if nextforest.Length = 0 then curforest else match Array.tryFind stable nextforest with | Some _ -> nextforest | None -> search nextforest search (stateChange start) |> Array.filter stable