Advent of Code 2015 Day 24 Part 2

Mix.install([
  {:kino_aoc, "~> 0.1"}
])

Get Inputs

{:ok, puzzle_input} =
  KinoAOC.download_puzzle("2015", "24", System.fetch_env!("LB_SESSION"))

My answer

packages = Enum.to_list(1..5) ++ Enum.to_list(7..11)

target_weight = packages |> Enum.sum() |> div(4)

for num_a <- packages,
    num_b <- packages,
    num_a < num_b,
    num_a + num_b == target_weight do
  [num_a, num_b]
end
|> Enum.uniq()
|> Enum.filter(&amp;(&amp;1 != []))
|> Enum.map(&amp;Enum.product(&amp;1))
|> Enum.min()

packages =
  puzzle_input
  |> String.split("\n")
  |> Enum.map(&String.to_integer(&1))

target_weight = packages |> Enum.sum() |> div(4)

defmodule Combinations do
  def all(_, 0), do: [[]]
  def all([], _), do: []
  def all(list, n) when length(list) == n, do: [list]

  def all([head | tail], n) do
    with_head = for combo <- all(tail, n - 1), do: [head | combo]
    without_head = all(tail, n)
    with_head ++ without_head
  end
end

1..length(packages)
|> Enum.reduce_while(nil, fn size, _ ->
  packages
  |> Combinations.all(size)
  |> Enum.filter(fn combo ->
    Enum.sum(combo) == target_weight
  end)
  |> case do
    [] ->
      {:cont, []}

    valid_combinations ->
      {:halt, valid_combinations}
  end
end)
|> Enum.map(&Enum.product(&1))
|> Enum.min()