FWIW, I tried with ets noticed slight gain compared to process dictionary.
On my machine, process dictionary takes ~13s and ets takes ~8s for part two.
defp next_turn(_hist, last, max_turns, max_turns), do: last
defp next_turn(hist, last, turn, max_turns) do
case :ets.lookup(hist, last) do
[] ->
true = :ets.insert(hist, {last, turn})
next_turn(hist, 0, turn + 1, max_turns)
[{_, prev_turn}] ->
true = :ets.insert(hist, {last, turn})
next_turn(hist, turn - prev_turn, turn + 1, max_turns)
end
end
def run(input, max_turns) do
hist = :ets.new(:hist, [])
true = :ets.insert(hist, Enum.with_index(input, 1))
next_turn(hist, List.last(input), length(input), max_turns)
end
