Day 2

Mix.install([
  {:zigler, "~> 0.13.3"}
])

Setups

sample = """
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
"""

defmodule Utils do
  def parse_input(input_text) do
    input_text
    |> String.split("\n", trim: true)
    |> Enum.map(
      &(String.split(&1, " ", trim: true)
        |> Enum.map(fn str_int -> String.to_integer(str_int) end))
    )
  end

  def load_text do
    File.read!("priv/day2.txt")
  end
end

Part 1

defmodule Part1 do
  def filter(row) do
    diffs =
      row
      |> Enum.chunk_every(2, 1, :discard)
      |> Enum.map(fn [left, right] -> left - right end)

    decreasing = Enum.all?(diffs, fn diff -> diff < 0 &amp;&amp; diff >= -3 end)
    increasing = Enum.all?(diffs, fn diff -> diff > 0 &amp;&amp; diff <= 3 end)

    decreasing || increasing
  end
end

sample 
|> Utils.parse_input
|> Enum.filter(&Part1.filter/1)
|> length

Utils.load_text() 
|> Utils.parse_input
|> Enum.filter(&Part1.filter/1)
|> length

Part 2

defmodule Part2 do
  def filter(row) do
    full_range = Enum.chunk_every(row, 2, 1, :discard)

    partial_ranges =
      row
      |> Enum.with_index()
      |> Enum.map(fn {_, at} ->
        List.delete_at(row, at) |> Enum.chunk_every(2, 1, :discard)
      end)

    [full_range | partial_ranges]
    |> Enum.any?(fn combo ->
      diffs = Enum.map(combo, fn [left, right] -> left - right end)
      
      decreasing = Enum.all?(diffs, fn diff -> diff < 0 &amp;&amp; diff >= -3 end)
      increasing = Enum.all?(diffs, fn diff -> diff > 0 &amp;&amp; diff <= 3 end)

      decreasing || increasing
    end)
  end
end

sample 
|> Utils.parse_input
|> Enum.filter(&Part2.filter/1)
|> length

Utils.load_text() 
|> Utils.parse_input
|> Enum.filter(&Part2.filter/1)
|> length

defmodule ZigZig do
  use Zig, otp_app: :zigler

  ~Z"""
  pub fn add_one(number: i64) i64 {
      return number + 1;
  }
  """
end

ZigZig.add_one(41)