Advent 2023 - Day 7

Mix.install([
  {:kino, "~> 0.11.3"}
])

Section

input = Kino.Input.textarea("Please paste your input file")

input =
  input
  |> Kino.Input.read()
  |> String.split("\n")
  |> Enum.map(fn line ->
    [hand, bid] = String.split(line, " ")
    hand = String.codepoints(hand)
    bid = bid |> Integer.parse() |> elem(0)
    {hand, bid}
  end)

[
  {["3", "2", "T", "3", "K"], 765},
  {["T", "5", "5", "J", "5"], 684},
  {["K", "K", "6", "7", "7"], 28},
  {["K", "T", "J", "J", "T"], 220},
  {["Q", "Q", "Q", "J", "A"], 483}
]

strength_of_card = fn strength_map, card ->
  if strength = Map.get(strength_map, card) do
    {card, strength}
  else
    {card, card |> Integer.parse() |> elem(0)}
  end
end

#Function<41.105768164/2 in :erl_eval.expr/6>

Part 1

first_ruleset_strength_map = %{
  "T" => 10,
  "J" => 11,
  "Q" => 12,
  "K" => 13,
  "A" => 14
}

%{"A" => 14, "J" => 11, "K" => 13, "Q" => 12, "T" => 10}

hands =
  input
  |> Enum.map(fn {hand, bid} ->
    hand_freq =
      hand
      |> Enum.map(fn card -> card end)
      |> Enum.frequencies_by(& &1)
      |> Map.values()
      |> Enum.sort()
      |> Enum.reverse()

    hand_strength =
      case hand_freq do
        [5] -> 7
        [4, 1] -> 6
        [3, 2] -> 5
        [3, 1, 1] -> 4
        [2, 2, 1] -> 3
        [2, 1, 1, 1] -> 2
        [1, 1, 1, 1, 1] -> 1
      end

    {hand_strength, hand, bid}
  end)

[
  {2, ["3", "2", "T", "3", "K"], 765},
  {4, ["T", "5", "5", "J", "5"], 684},
  {3, ["K", "K", "6", "7", "7"], 28},
  {3, ["K", "T", "J", "J", "T"], 220},
  {4, ["Q", "Q", "Q", "J", "A"], 483}
]

hands
|> Enum.sort(fn
  {hand_strength, lhand, _lbid}, {hand_strength, rhand, _rbid} ->
    contest =
      Enum.zip(lhand, rhand)
      |> Enum.find(fn
        {same_card, same_card} -> false
        {_not_the, _same_card} -> true
      end)

    if is_nil(contest) do
      raise "two of the same hand???"
    else
      {lcard, rcard} = contest
      lstrength = strength_of_card.(first_ruleset_strength_map, lcard)
      rstrength = strength_of_card.(first_ruleset_strength_map, rcard)

      lstrength < rstrength
    end

  {lhand_strength, _lhand, _lbid}, {rhand_strength, _rhand, _rbid} ->
    lhand_strength <= rhand_strength
end)
|> Enum.with_index()
|> Enum.map(fn {{_hand_strength, _hand, bid}, index} ->
  rank = index + 1
  score = bid * rank
  score
end)
|> Enum.sum()

6833

Part 2

hands =
  input
  |> Enum.map(fn {hand, bid} ->
    {j_count, freq} =
      hand
      |> Enum.map(fn {card, _strength} -> card end)
      |> Enum.frequencies_by(& &1)
      |> Map.pop("J")

    if j_count == 5 do
      raise "all jokers???"
    end

    freq =
      freq
      |> Map.values()
      |> Enum.sort()
      |> Enum.reverse()

    freq =
      if is_nil(j_count) do
        freq
      else
        freq |> List.update_at(0, &(&1 + j_count))
      end

    hand_strength =
      case freq do
        [5] -> 7
        [4, 1] -> 6
        [3, 2] -> 5
        [3, 1, 1] -> 4
        [2, 2, 1] -> 3
        [2, 1, 1, 1] -> 2
        [1, 1, 1, 1, 1] -> 1
      end

    {hand_strength, hand, bid}
  end)

[
  {2, [{"3", 3}, {"2", 2}, {"T", 10}, {"3", 3}, {"K", 13}], 765},
  {6, [{"T", 10}, {"5", 5}, {"5", 5}, {"J", 11}, {"5", 5}], 684},
  {3, [{"K", 13}, {"K", 13}, {"6", 6}, {"7", 7}, {"7", 7}], 28},
  {6, [{"K", 13}, {"T", 10}, {"J", 11}, {"J", 11}, {"T", 10}], 220},
  {6, [{"Q", 12}, {"Q", 12}, {"Q", 12}, {"J", 11}, {"A", 14}], 483}
]