day 4

Mix.install([
  {:kino, "~> 0.8.0"}
])

part 1

input = Kino.Input.textarea("paste input")

test_input = """
2-4,6-8
2-3,4-5
5-7,7-9
2-8,3-7
6-6,4-6
2-6,4-8
"""

defmodule P0 do
  def parse(input_str) do
    input_str
    |> String.split("\n", trim: true)
    |> Enum.map(&String.split(&1, ","))
    |> Enum.map(&parse_section/1)
  end

  def parse_section(sections) do
    sections
    |> Enum.map(fn section_str ->
      section_str
      |> String.split("-", trim: true)
      |> Enum.map(&String.to_integer/1)
      |> List.to_tuple()
    end)
  end
end

defmodule P1 do
  def calc(pairs) do
    pairs
    |> Enum.reduce(0, fn [{a, b}, {c, d}], acc ->
      r1 = a..b
      r2 = c..d

      if (Enum.member?(r2, a) and Enum.member?(r2, b)) or
           (Enum.member?(r1, c) and Enum.member?(r1, d)) do
        1 + acc
      else
        acc
      end
    end)
  end
end

test_input
|> P0.parse()
|> P1.calc()

input
|> Kino.Input.read()
|> P0.parse()
|> P1.calc()

Scratchpad

a = 1
b = 4
1..4 |> Enum.member?(3)
a..b |> Enum.member?(3)
1..10 |> Enum.member?(2..4)

test 1

ExUnit.start(auto_run: false)

defmodule P1Test do
  use ExUnit.Case, async: false

  test "calc" do
    assert """
           2-4,6-8
           2-3,4-5
           5-7,7-9
           2-8,3-7
           6-6,4-6
           2-6,4-8
           """
           |> P0.parse()
           |> P1.calc() == 2
  end
end

ExUnit.run()

part 2

defmodule P2 do
  def calc(pairs) do
    pairs
    |> Enum.reduce(0, fn [{a, b}, {c, d}], acc ->
      r1 = a..b
      r2 = c..d

      if Enum.member?(r2, a) or
           (Enum.member?(r2, b) and
              Enum.member?(r1, c)) or Enum.member?(r1, d) do
        1 + acc
      else
        acc
      end
    end)
  end
end

test_input
|> P0.parse()
|> P2.calc()

input
|> Kino.Input.read()
|> P0.parse()
|> P2.calc()

test 2

ExUnit.start(auto_run: false)

defmodule P2Test do
  use ExUnit.Case, async: false

  test "calc" do
    assert """
           2-4,6-8
           2-3,4-5
           5-7,7-9
           """
           |> P0.parse()
           |> P2.calc() == 1

    assert """
           2-4,6-8
           2-3,4-5
           5-7,7-9
           2-8,3-7
           6-6,4-6
           2-6,4-8
           """
           |> P0.parse()
           |> P2.calc() == 4
  end
end

ExUnit.run()