Day 1 - Advent of Code 2024

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

Setup

input = Kino.Input.textarea("Paste in your input:", default: "3   4
4   3
2   5
1   3
3   9
3   3")

Part 1

unsorted_lists =
  input
  |> Kino.Input.read()
  |> String.splitter("\n", trim: true)
  |> Stream.map(fn line ->
    [a, b] = line |> String.trim() |> String.split("   ")
    {String.to_integer(a), String.to_integer(b)}
  end)
  |> Enum.reduce([[], []], fn {a, b}, [unsorted_list_a, unsorted_list_b] ->
    [[a | unsorted_list_a], [b | unsorted_list_b]]
  end)

[list_a, list_b] =
  unsorted_lists
  |> Enum.map(&Task.async(fn -> Enum.sort(&1) end))
  |> Task.await_many()

list_a
|> Stream.zip(list_b)
|> Stream.map(fn {a, b} -> abs(a - b) end)
|> Enum.sum()

Part 2

freq_b = Enum.frequencies(list_b)

list_a
|> Stream.map(fn number -> number * Map.get(freq_b, number, 0) end)
|> Enum.sum()