Day 3

Section

Mix.install([{:kino, github: "livebook-dev/kino"}])

kino_input = Kino.Input.textarea("Paste input file:")

# input = Kino.Input.read(input)
input = """
00100
11110
10110
10111
10101
01111
00111
11100
10000
11001
00010
01010
"""

gamma_rate =
  input
  |> String.split("\n", trim: true)
  |> Enum.map(fn x -> String.split(x, "", trim: true) end)
  |> Enum.zip()
  |> Enum.map(fn x -> Enum.frequencies(Tuple.to_list(x)) end)
  |> Enum.map(fn %{"0" => x, "1" => y} ->
    if x > y do
      "0"
    else
      "1"
    end
  end)
  |> List.to_string()
  |> Integer.parse(2)
  |> elem(0)

epsilon_rate =
  input
  |> String.split("\n", trim: true)
  |> Enum.map(fn x -> String.split(x, "", trim: true) end)
  |> Enum.zip()
  |> Enum.map(fn x -> Enum.frequencies(Tuple.to_list(x)) end)
  |> Enum.map(fn %{"0" => x, "1" => y} ->
    if x < y do
      "0"
    else
      "1"
    end
  end)
  |> List.to_string()
  |> Integer.parse(2)
  |> elem(0)

gamma_rate * epsilon_rate

# Better solution to Part 1
Kino.Input.read(kino_input)
|> String.split("\n", trim: true)
|> Enum.map(fn line -> String.split(line, "", trim: true) end)
|> Enum.zip_with(&Enum.frequencies/1)
|> Enum.map(fn counts -> if counts["0"] > counts["1"], do: ["0", "1"], else: ["1", "0"] end)
|> Enum.zip_with(&Enum.join/1)
|> Enum.reduce(1, fn number, product -> String.to_integer(number, 2) * product end)

Part 2

# input = Kino.Input.read(input)
input = """
00100
11110
10110
10111
10101
01111
00111
11100
10000
11001
00010
01010
"""

input
|> String.split("\n", trim: true)
|> Enum.map(&String.split(&1, "", trim: true))
|> Enum.zip()
|> Enum.map(fn x -> Enum.frequencies(Tuple.to_list(x)) end)
|> Enum.max_by(fn x -> Map.values(x) end)
|> Enum.map(fn %{"0" => x, "1" => y} ->
  if x > y do
    "0"
  else
    "1"
  end
end)
|> List.to_string()
|> Integer.parse(2)
|> elem(0)

input = Kino.Input.textarea("Paste input file:")

defmodule Day3 do
  def input(input) do
    input
    |> String.split("\n", trim: true)
  end

  def oxygen([final_value], _position) do
    String.to_integer(final_value, 2)
  end

  def oxygen(data, position) do
    data
    |> Enum.group_by(fn num -> String.at(num, position) end)
    |> Enum.max_by(&number_sorter/1)
    |> elem(1)
    |> oxygen(position + 1)
  end

  def carbon([final_value], _position) do
    String.to_integer(final_value, 2)
  end

  def carbon(data, position) do
    data
    |> Enum.group_by(fn num -> String.at(num, position) end)
    |> Enum.min_by(&number_sorter/1)
    |> elem(1)
    |> carbon(position + 1)
  end

  defp number_sorter({target_bit, bit_list}) do
    length(bit_list) + 0.1 * String.to_integer(target_bit)
  end
end

data = Day3.input(Kino.Input.read(input))
Day3.oxygen(data, 0) * Day3.carbon(data, 0)