#AdventOfCode 2018 #elixir #elixirlang

6_chronal_coordinates.ex

defmodule ChronalCoordinates do
  def calc_part2(str_coords, threshold) do
    coords = parse_coords(str_coords)
    {bound_x, bound_y} = find_boundaries(coords)

    reduce_grid({bound_x, bound_y}, 0, fn x, y, acc ->
      sum = Enum.reduce(coords, 0, &sum_of_distances(&1, &2, {x, y}))
      if sum < threshold, do: acc + 1, else: acc
    end)
  end

  def calc_part1(str_coords) do
    coords = parse_coords(str_coords)
    boundaries = find_boundaries(coords)
    grid = populate_grid(coords, boundaries)
    infinites = find_infinites(grid, boundaries)

    Enum.reduce(grid, %{}, fn {id, _x, _y}, acc ->
      cond do
        id == 0 -> acc
        MapSet.member?(infinites, id) -> acc
        true -> Map.update(acc, id, 1, &(&1 + 1))
      end
    end)
    |> Enum.max_by(&elem(&1, 1))
    |> elem(1)
  end

  @doc """
  Calculates manhattan distance of two points

  iex> manhattan_distance({1, 1}, {1, 5})
  4

  iex> manhattan_distance({1, 5}, {10, 8})
  12
  """
  def manhattan_distance({x1, y1}, {x2, y2}) do
    abs(x1 - x2) + abs(y1 - y2)
  end

  def sum_of_distances({_, coord_x, coord_y}, acc, {x, y}) do
    acc + manhattan_distance({x, y}, {coord_x, coord_y})
  end

  def parse_coords(str_coords) do
    Enum.reduce(str_coords, {1, []}, fn str, {id, acc} ->
      [x, y] = String.split(str, ", ")
      {id + 1, [{id, String.to_integer(x), String.to_integer(y)} | acc]}
    end)
    |> elem(1)
    |> Enum.reverse()
  end

  def find_boundaries(coords \\ []) do
    Enum.reduce(coords, {0, 0}, fn {_id, x, y}, {max_x, max_y} ->
      {max(x + 1, max_x), max(y + 1, max_y)}
    end)
  end

  def populate_grid(points, {bound_x, bound_y}) do
    reduce_grid({bound_x, bound_y}, [], fn x, y, acc ->
      {id, _min_distance, _count} =
        Enum.reduce(points, {-1, :infinity, 0}, fn {id, px, py}, {old_id, min_distance, count} ->
          distance = manhattan_distance({x, y}, {px, py})

          cond do
            distance < min_distance -> {id, distance, 1}
            distance == min_distance -> {0, min_distance, count + 1}
            true -> {old_id, min_distance, count}
          end
        end)

      [{id, x, y} | acc]
    end)
    |> Enum.reverse()
  end

  def find_infinites(coords, boundaries) do
    Enum.reduce(coords, MapSet.new(), &reduce_infinite(&1, &2, boundaries))
  end

  defp reduce_infinite({id, x, y}, acc, {bound_x, bound_y})
       when (x == bound_x or y == bound_y or x == 0 or y == 0) and id != 0 do
    MapSet.put(acc, id)
  end

  defp reduce_infinite(_, acc, _), do: acc

  defp reduce_grid({bound_x, bound_y}, acc, fun) do
    Enum.reduce(0..bound_y, acc, fn y, acc ->
      Enum.reduce(0..bound_x, acc, fn x, acc ->
        fun.(x, y, acc)
      end)
    end)
  end
end

test = fn ->
  defmodule ChronalCoordinatesTest do
    use ExUnit.Case, async: true
    import ChronalCoordinates

    test "calculates manhattan distance" do
      assert 4 == manhattan_distance({1, 1}, {1, 5})
      assert 12 == manhattan_distance({1, 5}, {10, 8})
    end

    test "parses coordinates" do
      assert [{1, 2, 2}, {2, 3, 4}] == parse_coords(["2, 2", "3, 4"])
    end

    test "finds boundaries" do
      example = [
        {1, 1, 1},
        {2, 1, 6},
        {3, 8, 3},
        {4, 3, 4},
        {5, 5, 5},
        {6, 8, 9}
      ]

      assert {9, 10} == find_boundaries(example)
    end

    test "populates grid" do
      example = [
        {1, 1, 1},
        {2, 1, 6},
        {3, 8, 3},
        {4, 3, 4},
        {5, 5, 5},
        {6, 8, 9}
      ]

      result = [
        {1, 0, 0},
        {1, 1, 0},
        {1, 2, 0},
        {1, 3, 0},
        {1, 4, 0},
        {0, 5, 0},
        {3, 6, 0},
        {3, 7, 0},
        {3, 8, 0},
        {3, 9, 0},
        {1, 0, 1},
        {1, 1, 1},
        {1, 2, 1},
        {1, 3, 1},
        {1, 4, 1},
        {0, 5, 1},
        {3, 6, 1},
        {3, 7, 1},
        {3, 8, 1},
        {3, 9, 1},
        {1, 0, 2},
        {1, 1, 2},
        {1, 2, 2},
        {4, 3, 2},
        {4, 4, 2},
        {5, 5, 2},
        {3, 6, 2},
        {3, 7, 2},
        {3, 8, 2},
        {3, 9, 2},
        {1, 0, 3},
        {1, 1, 3},
        {4, 2, 3},
        {4, 3, 3},
        {4, 4, 3},
        {5, 5, 3},
        {3, 6, 3},
        {3, 7, 3},
        {3, 8, 3},
        {3, 9, 3},
        {0, 0, 4},
        {0, 1, 4},
        {4, 2, 4},
        {4, 3, 4},
        {4, 4, 4},
        {5, 5, 4},
        {5, 6, 4},
        {3, 7, 4},
        {3, 8, 4},
        {3, 9, 4},
        {2, 0, 5},
        {2, 1, 5},
        {0, 2, 5},
        {4, 3, 5},
        {5, 4, 5},
        {5, 5, 5},
        {5, 6, 5},
        {5, 7, 5},
        {3, 8, 5},
        {3, 9, 5},
        {2, 0, 6},
        {2, 1, 6},
        {2, 2, 6},
        {0, 3, 6},
        {5, 4, 6},
        {5, 5, 6},
        {5, 6, 6},
        {5, 7, 6},
        {0, 8, 6},
        {0, 9, 6},
        {2, 0, 7},
        {2, 1, 7},
        {2, 2, 7},
        {0, 3, 7},
        {5, 4, 7},
        {5, 5, 7},
        {5, 6, 7},
        {6, 7, 7},
        {6, 8, 7},
        {6, 9, 7},
        {2, 0, 8},
        {2, 1, 8},
        {2, 2, 8},
        {0, 3, 8},
        {5, 4, 8},
        {5, 5, 8},
        {6, 6, 8},
        {6, 7, 8},
        {6, 8, 8},
        {6, 9, 8},
        {2, 0, 9},
        {2, 1, 9},
        {2, 2, 9},
        {0, 3, 9},
        {6, 4, 9},
        {6, 5, 9},
        {6, 6, 9},
        {6, 7, 9},
        {6, 8, 9},
        {6, 9, 9}
      ]

      boundries = {9, 9}

      assert result == populate_grid(example, boundries)
    end

    test "find infinites" do
      example = [
        {1, 0, 0},
        {1, 1, 0},
        {1, 2, 0},
        {1, 3, 0},
        {1, 4, 0},
        {0, 5, 0},
        {3, 6, 0},
        {3, 7, 0},
        {3, 8, 0},
        {3, 9, 0},
        {1, 0, 1},
        {1, 1, 1},
        {1, 2, 1},
        {1, 3, 1},
        {1, 4, 1},
        {0, 5, 1},
        {3, 6, 1},
        {3, 7, 1},
        {3, 8, 1},
        {3, 9, 1},
        {1, 0, 2},
        {1, 1, 2},
        {1, 2, 2},
        {4, 3, 2},
        {4, 4, 2},
        {5, 5, 2},
        {3, 6, 2},
        {3, 7, 2},
        {3, 8, 2},
        {3, 9, 2},
        {1, 0, 3},
        {1, 1, 3},
        {4, 2, 3},
        {4, 3, 3},
        {4, 4, 3},
        {5, 5, 3},
        {3, 6, 3},
        {3, 7, 3},
        {3, 8, 3},
        {3, 9, 3},
        {0, 0, 4},
        {0, 1, 4},
        {4, 2, 4},
        {4, 3, 4},
        {4, 4, 4},
        {5, 5, 4},
        {5, 6, 4},
        {3, 7, 4},
        {3, 8, 4},
        {3, 9, 4},
        {2, 0, 5},
        {2, 1, 5},
        {0, 2, 5},
        {4, 3, 5},
        {5, 4, 5},
        {5, 5, 5},
        {5, 6, 5},
        {5, 7, 5},
        {3, 8, 5},
        {3, 9, 5},
        {2, 0, 6},
        {2, 1, 6},
        {2, 2, 6},
        {0, 3, 6},
        {5, 4, 6},
        {5, 5, 6},
        {5, 6, 6},
        {5, 7, 6},
        {0, 8, 6},
        {0, 9, 6},
        {2, 0, 7},
        {2, 1, 7},
        {2, 2, 7},
        {0, 3, 7},
        {5, 4, 7},
        {5, 5, 7},
        {5, 6, 7},
        {6, 7, 7},
        {6, 8, 7},
        {6, 9, 7},
        {2, 0, 8},
        {2, 1, 8},
        {2, 2, 8},
        {0, 3, 8},
        {5, 4, 8},
        {5, 5, 8},
        {6, 6, 8},
        {6, 7, 8},
        {6, 8, 8},
        {6, 9, 8},
        {2, 0, 9},
        {2, 1, 9},
        {2, 2, 9},
        {0, 3, 9},
        {6, 4, 9},
        {6, 5, 9},
        {6, 6, 9},
        {6, 7, 9},
        {6, 8, 9},
        {6, 9, 9}
      ]

      boundries = {9, 9}

      result = MapSet.new([1, 2, 3, 6])
      assert result == find_infinites(example, boundries)
    end

    test "solves part#1" do
      example =
        """
        1, 1
        1, 6
        8, 3
        3, 4
        5, 5
        8, 9
        """
        |> String.split("\n", trim: true)

      assert 17 == calc_part1(example)
    end

    test "solves part#2" do
      example =
        """
        1, 1
        1, 6
        8, 3
        3, 4
        5, 5
        8, 9
        """
        |> String.split("\n", trim: true)

      assert 16 == calc_part2(example, 32)
    end
  end
end

case System.argv() do
  ["--test"] ->
    ExUnit.start()
    test.()

  _ ->
    # File.read!("./furkan_input.txt")
    result1 =
      File.read!("./6_chronal_coordinates_input.txt")
      |> String.split("\n", trim: true)
      |> ChronalCoordinates.calc_part1()

    IO.puts("Result of part#1 is... #{result1}")

    result2 =
      File.read!("./6_chronal_coordinates_input.txt")
      |> String.split("\n", trim: true)
      |> ChronalCoordinates.calc_part2(10_000)

    IO.puts("Result of part#2 is... #{result2}")
end

6_chronal_coordinates_input.ex

224, 153
176, 350
353, 241
207, 59
145, 203
123, 210
113, 203
191, 241
172, 196
209, 249
260, 229
98, 231
305, 215
258, 141
337, 282
156, 140
325, 197
179, 279
283, 233
317, 150
305, 245
67, 109
251, 140
245, 59
173, 105
59, 173
257, 70
269, 110
102, 162
179, 180
324, 112
357, 311
317, 245
239, 112
321, 220
133, 97
334, 99
117, 102
133, 112
222, 316
68, 296
150, 287
263, 263
66, 347
128, 118
63, 202
68, 236
264, 122
77, 243
92, 110

README.md

Getting Started

1. Make sure you have elixir installed and running. (Hint: elixir --version)
2. Download all gist files and run elixir 6_chronal_coordinates.ex. That will compile the code and give you results.
3. Run elixir 5_chronal_coordinates.ex --test to run tests.
4. Have more fun!