Day 07

Setup

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

input = Kino.Input.textarea("Puzzle Input")

Example Data: 16,1,2,0,4,2,7,1,2,14

Part 1

input
|> Kino.Input.read()
|> String.split(",")
|> Enum.map(&String.to_integer/1)
|> then(fn initial ->
  for i <- Enum.min(initial)..Enum.max(initial) do
    Enum.map(initial, fn p -> abs(i - p) end) |> Enum.sum()
  end
  |> Enum.min()
end)

Part 2

defmodule Day7 do
  def fuel_recur(0, fuel), do: fuel

  def fuel_recur(dist, fuel) do
    fuel_recur(dist - 1, fuel + dist)
  end
end

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

for i <- Enum.min(initial)..Enum.max(initial) do
  Enum.map(initial, fn position ->
    Day7.fuel_recur(abs(position - i), 0)
  end)
  |> Enum.sum()
end
|> Enum.min()

Part 1 Refactor

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

median_index = div(length(initial_positions) - 1, 2)

Enum.sort(initial_positions)
|> Enum.slice(median_index, 2)
|> Enum.map(fn destination ->
  Enum.map(initial_positions, fn position ->
    abs(destination - position)
  end)
  |> Enum.sum()
end)
|> Enum.min()

Part 2 Refactor

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

mean = Enum.sum(initial_positions) / length(initial_positions)

floor(mean)..ceil(mean)
|> Enum.map(fn destination ->
  Enum.map(initial_positions, fn position ->
    n = abs(destination - position)
    (n + 1) * n / 2
  end)
  |> Enum.sum()
  |> floor()
end)
|> Enum.min()