AoC 2015 Day 3

Mix.install([:kino])

defmodule Utils do
  def split(line, sep \\ "") do
    String.split(line, sep, trim: true)
  end

  def split_all_lines(text, sep \\ "") do
    text
    |> String.split("\n", trim: true)
    |> Enum.map(&split(&1, sep))
  end

  def to_numbers(number) when is_binary(number) do
    String.to_integer(number)
  end

  def to_numbers(numbers) when is_list(numbers) do
    Enum.map(numbers, &to_numbers/1)
  end

  def to_matrix(text, sep \\ "") do
    text
    |> split_all_lines(sep)
    |> then(fn data ->
      for {row, r} <- Enum.with_index(data), {col, c} <- Enum.with_index(row) do
        {{r, c}, col}
      end
    end)
    |> Map.new()
  end
end

Setup

import Utils

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

text = Kino.Input.read(input)

data = split(text, "")

P1

p1 = fn data ->
  Enum.reduce(data, {{0, 0}, MapSet.new([{0, 0}])}, fn
    "^", {{x, y}, s} ->
      curr = {x, y + 1}
      {curr, MapSet.put(s, curr)}

    "v", {{x, y}, s} ->
      curr = {x, y - 1}
      {curr, MapSet.put(s, curr)}

    "<", {{x, y}, s} ->
      curr = {x - 1, y}
      {curr, MapSet.put(s, curr)}

    ">", {{x, y}, s} ->
      curr = {x + 1, y}
      {curr, MapSet.put(s, curr)}
  end)
  |> elem(1)
end

p1.(data) |> Enum.count()

P2

{flesh, robot} =
  data
  |> Enum.with_index()
  |> Enum.split_with(fn {_, i} -> rem(i, 2) == 0 end)

flesh
|> Enum.map(&elem(&1, 0))
|> p1.()
|> MapSet.union(robot |> Enum.map(&elem(&1, 0)) |> p1.())
|> Enum.count()