Day 7: Camel Cards

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

Input

input = Kino.Input.textarea("Please, paste your input here:")

defmodule Day7Shared do
  def parse(input, j_for_jokers \\ false) do
    input
    |> Kino.Input.read()
    |> String.split("\n")
    |> Enum.map(fn line ->
      [raw_hand, bid] = String.split(line, ~r/\s+/)

      hand = parse_hand(raw_hand, j_for_jokers)
      bid = String.to_integer(bid)

      {raw_hand, hand, bid}
    end)
  end

  defp parse_hand(raw_hand, j_for_jokers) do
    raw_hand
    |> String.split("", trim: true)
    |> Enum.map(fn card ->
      case card do
        "2" -> 2
        "3" -> 3
        "4" -> 4
        "5" -> 5
        "6" -> 6
        "7" -> 7
        "8" -> 8
        "9" -> 9
        "T" -> 10
        "J" -> if(j_for_jokers, do: 1, else: 11)
        "Q" -> 12
        "K" -> 13
        "A" -> 14
      end
    end)
  end
end

Day7Shared.parse(input)

Part 1

defmodule Day7Part1 do
  def solve(hands) do
    hands
    |> Enum.map(fn {raw_hand, hand, bid} -> {raw_hand, hand, kind(hand), bid} end)
    |> Enum.group_by(fn {_, _, kind, _} -> kind end)
    |> Enum.map(fn {kind, hands} -> {kind, Enum.sort(hands, &compare/2)} end)
    |> Enum.into(%{})
    |> Enum.sort()
    |> Enum.reduce({0, 1}, fn {_kind, hands}, {total, rank} ->
      Enum.reduce(hands, {total, rank}, fn {_, _, _, bid}, {total, rank} ->
        {total + rank * bid, rank + 1}
      end)
    end)
    |> elem(0)
  end

  defp kind(hand) do
    case Enum.sort(hand) do
      [a, a, a, a, a] -> 6
      [a, a, a, a, _] -> 5
      [_, a, a, a, a] -> 5
      [a, a, a, b, b] -> 4
      [a, a, b, b, b] -> 4
      [a, a, a, _, _] -> 3
      [_, _, a, a, a] -> 3
      [_, a, a, a, _] -> 3
      [a, a, b, b, _] -> 2
      [a, a, _, b, b] -> 2
      [_, a, a, b, b] -> 2
      [a, a, _, _, _] -> 1
      [_, a, a, _, _] -> 1
      [_, _, a, a, _] -> 1
      [_, _, _, a, a] -> 1
      _ -> 0
    end
  end

  defp compare({_, left, _, _}, {_, right, _, _}), do: left < right
end

input
|> Day7Shared.parse()
|> Day7Part1.solve()

Part 2

defmodule Day7Part2 do
  def solve(hands) do
    hands
    |> Enum.map(fn {raw_hand, hand, bid} -> {raw_hand, hand, kind(hand), bid} end)
    # |> Enum.filter(fn {_, hand, _, _} -> 1 in hand end)
    |> Enum.group_by(fn {_, _, kind, _} -> kind end)
    |> Enum.map(fn {kind, hands} -> {kind, Enum.sort(hands, &compare/2)} end)
    |> Enum.into(%{})
    |> Enum.sort()
    |> Enum.reduce({0, 1}, fn {_kind, hands}, {total, rank} ->
      Enum.reduce(hands, {total, rank}, fn {_, _, _, bid}, {total, rank} ->
        {total + rank * bid, rank + 1}
      end)
    end)
    |> elem(0)
  end

  defp kind(hand) do
    {jokers, rest} = Enum.split_with(hand, &(&1 == 1))

    jokers
    |> length()
    |> kind(rest)
  end

  defp kind(0, hand) do
    case Enum.sort(hand) do
      # five
      [a, a, a, a, a] -> 6
      # four
      [a, a, a, a, _] -> 5
      # four
      [_, a, a, a, a] -> 5
      # full
      [a, a, a, b, b] -> 4
      # full
      [a, a, b, b, b] -> 4
      # three
      [a, a, a, _, _] -> 3
      # three
      [_, _, a, a, a] -> 3
      # three
      [_, a, a, a, _] -> 3
      # two
      [a, a, b, b, _] -> 2
      # two
      [a, a, _, b, b] -> 2
      # two
      [_, a, a, b, b] -> 2
      # one
      [a, a, _, _, _] -> 1
      # one
      [_, a, a, _, _] -> 1
      # one
      [_, _, a, a, _] -> 1
      # one
      [_, _, _, a, a] -> 1
      _ -> 0
    end
  end

  defp kind(1, hand) do
    case Enum.sort(hand) do
      [a, a, a, a] -> 6
      [a, a, a, _] -> 5
      [_, a, a, a] -> 5
      [a, a, b, b] -> 4
      [a, a, _, _] -> 3
      [_, a, a, _] -> 3
      [_, _, a, a] -> 3
      _ -> 1
    end
  end

  defp kind(2, hand) do
    case Enum.sort(hand) do
      [a, a, a] -> 6
      [a, a, _] -> 5
      [_, a, a] -> 5
      _ -> 3
    end
  end

  defp kind(3, hand) do
    case Enum.sort(hand) do
      [a, a] -> 6
      _ -> 5
    end
  end

  defp kind(4, _hand), do: 6
  defp kind(5, _hand), do: 6

  defp compare({_, left, _, _}, {_, right, _, _}), do: left < right
end

input
|> Day7Shared.parse(true)
|> Day7Part2.solve()

# 253273139 too high
# 26690403 too low
# 253253225 is the right answer!