Day 22 was super fun! I was thinking of waiting for the morning but the puzzle was begging me to do a quick mix solve 2020 22 and go for it!
defmodule AdventOfCode.Y2020.Day22 do
use AdventOfCode.Helpers.InputReader, year: 2020, day: 22
def run_1, do: input!() |> process() |> play() |> score()
def run_2, do: input!() |> process() |> play_rec() |> score()
def process(deal), do: decks(Enum.map(String.split(deal, "\n\n"), &String.split(&1, ":")))
defp score(cards) do
Enum.reduce(Enum.with_index(Enum.reverse(cards), 1), 0, fn {val, idx}, score ->
score + val * idx
end)
end
defp decks([[_, human], [_, crab]]), do: {deck(human), deck(crab)}
defp deck(p), do: Enum.map(String.split(p, "\n", trim: true), &String.to_integer/1)
defp play({[], crab}), do: crab
defp play({human, []}), do: human
defp play({[h | human], [c | crab]}) when h > c, do: play({human ++ [h, c], crab})
defp play({[h | human], [c | crab]}), do: play({human, crab ++ [c, h]})
defp play_rec(decks), do: elem(play_rec(decks, {[], []}), 1)
defp play_rec({[], crab}, _), do: {2, crab}
defp play_rec({human, []}, _), do: {1, human}
defp play_rec({[h | hs] = human, [c | cs] = crab}, {humans, crabs}) do
if human in humans || crab in crabs do
{1, human}
else
memo = {[human | humans], [crab | crabs]}
if h <= length(hs) && c <= length(cs) do
case play_rec({Enum.take(hs, h), Enum.take(cs, c)}, {[], []}) do
{1, _} -> play_rec({hs ++ [h, c], cs}, memo)
{2, _} -> play_rec({hs, cs ++ [c, h]}, memo)
end
else
(h > c && play_rec({hs ++ [h, c], cs}, memo)) || play_rec({hs, cs ++ [c, h]}, memo)
end
end
end
end
I’m not experienced with Elixir, I just did some small hobby projects with Phoenix, and already it’s easier for me to read/write Erlang, just because of the time i spent with it.
