Day 2

Mix.install([
  {:kino, "~> 0.13.0"}
])

Part 1

content =
  Kino.FS.file_path("day2.txt")
  |> File.read!()
  |> String.trim()

defmodule SeqTest do
  def increasing?(list) do
    list
    |> Enum.chunk_every(2, 1, :discard)
    |> Enum.reduce(true, fn [a, b], acc ->
      acc and (b - a <= 3 and b - a > 0)
    end)
  end

  def decreasing?(list) do
    list
    |> Enum.chunk_every(2, 1, :discard)
    |> Enum.reduce(true, fn [a, b], acc ->
      acc and (a - b <= 3 and a - b > 0)
    end)
  end
end

safe_reports =
  content
  |> String.split("\n")
  |> Enum.map(fn line ->
    String.split(line)
    |> Enum.map(fn num -> String.to_integer(num) end)
  end)
  |> Enum.count(fn line ->
    SeqTest.increasing?(line) or SeqTest.decreasing?(line)
  end)

Part 2

defmodule Dampener do
  def dampened_lists(report) do
    for i <- 0..(length(report) - 1) do
      List.delete_at(report, i)
    end
  end
end

safe_problem_dampener =
  content
  |> String.split("\n")
  |> Enum.map(fn line ->
    String.split(line)
    |> Enum.map(fn num -> String.to_integer(num) end)
  end)
  |> Enum.count(fn line ->
    line
    |> Dampener.dampened_lists()
    |> Enum.any?(fn single -> SeqTest.increasing?(single) or SeqTest.decreasing?(single) end)
  end)