Advent of Code Day 7

Setup

test_input = """
16,1,2,0,4,2,7,1,2,14
"""

input = File.read!("day_07/input.txt")

defmodule Setup do
  def parse(input) when is_binary(input) do
    input
    |> String.trim()
    |> String.split(",")
    |> Enum.map(&String.to_integer/1)
  end
end

{:module, Setup, <<70, 79, 82, 49, 0, 0, 6, ...>>, {:parse, 1}}

Part 1

defmodule DaySevenPart1 do
  def fuel_used(positions) do
    {min, max} = Enum.min_max(positions)

    Enum.reduce(min..max, %{}, fn target_pos, acc ->
      Map.put(acc, target_pos, fuel_used_for_position(positions, target_pos))
    end)
    |> Enum.to_list()
    |> Enum.min(fn {_, left_fuel}, {_, right_fuel} ->
      left_fuel <= right_fuel
    end)
  end

  def fuel_used_for_position(positions, target_pos) do
    positions
    |> Enum.reduce([], fn pos, acc ->
      [abs(pos - target_pos) | acc]
    end)
    |> Enum.sum()
  end
end

data = Setup.parse(input)
DaySevenPart1.fuel_used(data)

{321, 335330}

Part 2

defmodule DaySevenPart2 do
  def fuel_used(positions) do
    {min, max} = Enum.min_max(positions)

    Enum.reduce(min..max, %{}, fn target_pos, acc ->
      Map.put(acc, target_pos, fuel_used_for_position(positions, target_pos))
    end)
    |> Enum.to_list()
    |> Enum.min(fn {_, left_fuel}, {_, right_fuel} ->
      left_fuel <= right_fuel
    end)
  end

  def fuel_used_for_position(positions, target_pos) do
    positions
    |> Enum.reduce([], fn pos, acc ->
      distance = abs(pos - target_pos)
      [Enum.sum(distance..0) | acc]
    end)
    |> Enum.sum()
  end
end

data = Setup.parse(input)
DaySevenPart2.fuel_used(data)

{457, 92439766}