🎄 Year 2025 🔔 Day 03

Section

batteries =
  File.read!("#{__DIR__}/../../../inputs/2025/day03.txt")
  |> String.split("\n", trim: true)
  |> Enum.map(fn line ->
    line
    |> String.graphemes()
    |> Enum.map(&String.to_integer/1)
  end)

Part 1

batteries
|> Enum.map(fn battery ->
  max_first = battery |> Enum.take(Enum.count(battery) - 1) |> Enum.max()
  max_second = battery |> Enum.drop_while(&(&1 != max_first)) |> Enum.drop(1) |> Enum.max()
  Integer.undigits([max_first, max_second])
end)
|> Enum.sum()

Part 2

defmodule Helper do
  def recursive_solve(battery, solution \\ [], remaining \\ 12)
  def recursive_solve(_, solution, 0), do: Integer.undigits(Enum.reverse(solution))
  def recursive_solve(battery, solution, remaining) do
    max_n = battery |> Enum.take(Enum.count(battery) - (remaining - 1)) |> Enum.max()
    remaining_battery = battery |> Enum.drop_while(&(&1 != max_n)) |> Enum.drop(1)

    recursive_solve(remaining_battery, [max_n | solution], remaining - 1)
  end
end

batteries
|> Enum.map(&Helper.recursive_solve/1)
|> Enum.sum()