Advent of code 2021 - day 4 - part 1 - solution

advent-of-code-2021-day4.exs

defmodule Bingo do
  def parseline(line) do
    line
    |> String.split(" ", trim: true)
    |> Enum.map(&String.to_integer/1)
  end

  def parseboard(board) do
    Enum.map(board, &parseline/1)
  end

  def read(path) do
    input = File.read!(path)
    input = String.split(input, "\n")
    [numbers | boards] = input

    numbers = numbers |> String.split(",") |> Enum.map(&String.to_integer/1)

    boards =
      boards
      |> Enum.chunk_by(fn x -> x != "" end)
      |> Enum.reject(fn x -> x == [""] end)
      |> Enum.map(&parseboard/1)

    %{boards: boards, numbers: numbers}
  end

  def checkboard(board, history) do
    vertical = board

    horizontal =
      board
      |> Enum.map(fn line -> MapSet.subset?(MapSet.new(line), history) end)
      |> Enum.find_index(fn line -> line == true end)

    vertical =
      vertical
      |> Enum.zip()
      |> Enum.map(&Tuple.to_list(&1))
      |> Enum.map(fn line -> MapSet.subset?(MapSet.new(line), history) end)
      |> Enum.find_index(fn line -> line == true end)

    {horizontal, vertical}
  end

  def checkboards(history, boards) do
    history = MapSet.new(history)

    boards
    |> Enum.map(fn board -> checkboard(board, history) end)
    |> Enum.find_index(fn result -> result != {nil, nil} end)
  end

  def count(boards, winner, history) do
    board = boards |> Enum.at(winner)
    latest = history |> Enum.at(-1)
    history = MapSet.new(history)

    s =
      board
      |> Enum.map(fn line -> Enum.filter(line, fn x -> !MapSet.member?(history, x) end) end)
      |> Enum.map(&Enum.sum/1)
      |> Enum.sum()

    result = s * latest
    {board, result, latest, history}
  end

  def play(history, future, boards, winner) when future == [] or winner != nil do
    if winner != nil do
      count(boards, winner, history)
    else
      "No winner"
    end
  end

  def play(history, future, boards, _winner) do
    [next | future] = future
    curr = history ++ [next]
    play(curr, future, boards, checkboards(curr, boards))
  end

  def run() do
    input = read("./input/day4.txt")
    {history, future} = Enum.split(input[:numbers], 4)
    play(history, future, input[:boards], nil)
  end
end