Day 02

Mix.install([
  {:kino, "~> 0.14.2"}
])

IEx.Helpers.c("/Users/johnb/dev/2024adventOfCode/advent_of_code.ex")
alias AdventOfCode, as: AOC
alias Kino.Input

# Note: when making the next template, something like this works well:
#   `cat day04.livemd | sed 's/03/04/' > day04.livemd`
#

Installation and Data

input_p1example = Kino.Input.textarea("Example Data")

input_p1puzzleInput = Kino.Input.textarea("Puzzle Input")

input_source_select =
  Kino.Input.select("Source", [{:example, "example"}, {:puzzle_input, "puzzle input"}])

p1data = fn ->
  (Kino.Input.read(input_source_select) == :example &&
     Kino.Input.read(input_p1example)) ||
    Kino.Input.read(input_p1puzzleInput)
end

Solution

defmodule Day02 do
  def parse(text) do
    text
    |> AOC.as_single_lines()
    |> Enum.map(fn line ->
      line
      |> String.split(~r/\W+/, trim: true)
      |> Enum.map(&String.to_integer/1)
    end)
  end

  def is_increasing?(report) do
    report
    |> Enum.chunk_every(2, 1, :discard)
    |> Enum.all?(fn [left, right] -> right > left &amp;&amp; (right - left <= 3) end)
  end

  def is_decreasing?(report) do
    report
    |> Enum.reverse()
    |> is_increasing?()
  end
  
  def solve1(text) do
    data = parse(text)

    data
    |> Enum.filter(fn report ->
      is_increasing?(report) || is_decreasing?(report)
    end)
    |> Enum.count()
  end

  def is_safe_without_one?(report) do
    report
    |> Enum.with_index()
    |> Enum.any?(fn {_item, index} -> 
      {_, shorter_report} = List.pop_at(report, index)
      is_increasing?(shorter_report) || is_decreasing?(shorter_report)
    end)
  end

  def solve2(text) do
    data = parse(text)

    data
    |> Enum.filter(fn report ->
      is_increasing?(report) || is_decreasing?(report) || is_safe_without_one?(report)
    end)
    |> Enum.count()
  end
end

# Example:
# 7 6 4 2 1
# 1 2 7 8 9
# 9 7 6 2 1
# 1 3 2 4 5
# 8 6 4 4 1
# 1 3 6 7 9

p1data.()
|> Day02.solve1()
|> IO.inspect(label: "\n*** Part 1 solution (example: 2)")
# 356

p1data.()
|> Day02.solve2()
|> IO.inspect(label: "\n*** Part 2 solution (example: 4)")
# 413