Advent of Code 2023 Day 9

Mix.install([
  {:kino, "~> 0.11.3"}
])

Section

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

defmodule Oasis do
  def parse(input) do
    Kino.Input.read(input)
    |> String.split("\n", trim: true)
    |> Enum.map(fn row -> Enum.map(String.split(row, " ", trim: true), &String.to_integer/1) end)
  end

  def process_row(row, rows) do
    next_row =
      row
      |> Enum.map(fn [first, second] -> second - first end)
      |> Enum.chunk_every(2, 1, :discard)

    if List.flatten(next_row) |> Enum.uniq() == [0] do
      [row | rows]
    else
      process_row(next_row, [row | rows])
    end
  end

  def calculate_row(row, right \\ true) do
    row =
      process_row(Enum.chunk_every(row, 2, 1, :discard), [])
      |> Enum.chunk_every(2, 1, :discard)

    new_row =
      if right do
        row =
          Enum.map(row, fn row ->
            [Enum.at(Enum.at(Enum.at(row, 0), -1), 1), Enum.at(Enum.at(Enum.at(row, 1), -1), 1)]
          end)

        [
          Enum.at(hd(row), 0) + Enum.at(hd(row), 1)
          | Enum.map(tl(row), fn row -> Enum.at(row, 1) end)
        ]
      else
        row =
          Enum.map(row, fn row ->
            [Enum.at(Enum.at(Enum.at(row, 0), 0), 0), Enum.at(Enum.at(Enum.at(row, 1), 0), 0)]
          end)

        [
          Enum.at(hd(row), 1) - Enum.at(hd(row), 0)
          | Enum.map(tl(row), fn row -> Enum.at(row, 1) end)
        ]
      end

    new_row
    |> Enum.reduce(0, fn cell, acc -> if right, do: acc + cell, else: cell - acc end)
  end

  def p1(input) do
    parse(input)
    |> Enum.map(fn row -> calculate_row(row) end)
    |> Enum.sum()
  end

  def p2(input) do
    parse(input)
    |> Enum.map(fn row -> calculate_row(row, false) end)
    |> Enum.sum()
  end
end

Oasis.p1(input)

Oasis.p2(input)