Day 7

Setup

Mix.install(
  [
    {:kino, "~> 0.4.1"}
  ],
  consolidate_protocols: false
)

input = Kino.Input.text("Please paste your input:")

lines =
  input
  |> Kino.Input.read()
  |> String.split(",", trim: true)
  |> Enum.map(&String.to_integer/1)

Part 1

defmodule Day7 do
  def balance_positions(list, target) do
    Enum.reduce(list, 0, fn position, fuel ->
      fuel + abs(target - position)
    end)
  end
end

max = Enum.max(lines)
min = Enum.min(lines)

lines
|> Day7.balance_positions(2)

Enum.reduce(min..max, {lines, 0}, fn target, {lines, lowest_fuel} ->
  fuel = Day7.balance_positions(lines, target)

  {lines,
   if fuel < lowest_fuel || lowest_fuel == 0 do
     fuel
   else
     lowest_fuel
   end}
end)

Part 2

defmodule Day7 do
  def calculate_fuel(_delta = 0, _next_fuel, total_fuel) do
    total_fuel
  end

  def calculate_fuel(delta, next_fuel, total_fuel) do
    calculate_fuel(delta - 1, next_fuel + 1, total_fuel + next_fuel)
  end

  def balance_positions2(list, target) do
    Enum.reduce(list, 0, fn position, fuel ->
      fuel + Day7.calculate_fuel(abs(target - position), 1, 0)
    end)
  end
end

max = Enum.max(lines)
min = Enum.min(lines)

lines
|> Day7.balance_positions2(2)

Enum.reduce(min..max, {lines, 0}, fn target, {lines, lowest_fuel} ->
  fuel = Day7.balance_positions2(lines, target)

  {lines,
   if fuel < lowest_fuel || lowest_fuel == 0 do
     fuel
   else
     lowest_fuel
   end}
end)

16 - 5
1 + 2 + 3 + 4 + 5 + 6 + 7 + 8 + 9 + 10 + 11