Solve 2021 Day 5 in elixir

2021/Day5/Elixir/hydrothermal_venture.ex

@@ -0,0 +1,148 @@
+defmodule HypothermalVenture do
+  @type line :: %{
+          from: {integer, integer},
+          to: {integer, integer}
+        }
+
+  def load_file() do
+    File.read!("../input.txt")
+    |> String.split("\n", trim: true)
+  end
+
+  def parse_line({from, to}) do
+    %{
+      from:
+        String.split(from, ",")
+        |> Enum.map(&Integer.parse/1)
+        |> Enum.map(&elem(&1, 0))
+        |> List.to_tuple(),
+      to:
+        String.split(to, ",")
+        |> Enum.map(&Integer.parse/1)
+        |> Enum.map(&elem(&1, 0))
+        |> List.to_tuple()
+    }
+  end
+
+  @spec parse_lines(input :: [String.t()]) :: [line]
+  def parse_lines(input) do
+    Enum.map(input, fn ln ->
+      String.replace(ln, " ", "")
+      |> String.split("->", trim: true)
+      |> List.to_tuple()
+      |> parse_line()
+    end)
+  end
+
+  def init_array(), do: Matrix.from_list(List.duplicate(List.duplicate(0, 1000), 1000))
+
+  def draw_line(matrix, %{from: {x1, y1}, to: {x2, y2}} = line)
+      when x2 - x1 == 0 and y2 - y1 == 0 do
+    put_in(matrix[y1][x1], matrix[y1][x1] + 1)
+  end
+
+  def draw_line(matrix, %{from: {x1, y1}, to: {x2, y2}}) do
+    delta_x = x2 - x1
+    delta_y = y2 - y1
+
+    updated_matrix = put_in(matrix[y1][x1], matrix[y1][x1] + 1)
+
+    new_x =
+      case delta_x do
+        x when x > 0 -> x1 + 1
+        x when x < 0 -> x1 - 1
+        x when x == 0 -> x1
+      end
+
+    new_y =
+      case delta_y do
+        y when y > 0 -> y1 + 1
+        y when y < 0 -> y1 - 1
+        y when y == 0 -> y1
+      end
+
+    draw_line(updated_matrix, %{from: {new_x, new_y}, to: {x2, y2}})
+  end
+
+  def draw_lines(matrix, []), do: matrix
+  def draw_lines(matrix, [line | tail]), do: draw_lines(draw_line(matrix, line), tail)
+
+  def solve(lines) do
+    matrix = init_array()
+
+    draw_lines(matrix, lines)
+    |> Matrix.to_list()
+    |> List.flatten()
+    |> Enum.filter(fn x -> x >= 2 end)
+    |> Enum.count()
+  end
+
+  @spec first() :: Integer
+  def first() do
+    lines =
+      load_file()
+      |> parse_lines()
+      |> Enum.filter(fn %{from: {x1, y1}, to: {x2, y2}} -> x1 == x2 or y1 == y2 end)
+
+    solve(lines)
+  end
+
+  @spec second() :: Integer
+  def second() do
+    lines =
+      load_file()
+      |> parse_lines()
+
+    solve(lines)
+  end
+end
+
+defmodule Matrix do
+  @moduledoc """
+  Helpers for working with multidimensional lists, also called matrices.
+  """
+
+  @doc """
+  Converts a multidimensional list into a zero-indexed map.
+
+  ## Example
+
+      iex> list = [["x", "o", "x"]]
+      ...> Matrix.from_list(list)
+      %{0 => %{0 => "x", 1 => "o", 2 => "x"}}
+  """
+  def from_list(list) when is_list(list) do
+    do_from_list(list)
+  end
+
+  defp do_from_list(list, map \\ %{}, index \\ 0)
+  defp do_from_list([], map, _index), do: map
+
+  defp do_from_list([h | t], map, index) do
+    map = Map.put(map, index, do_from_list(h))
+    do_from_list(t, map, index + 1)
+  end
+
+  defp do_from_list(other, _, _), do: other
+
+  @doc """
+  Converts a zero-indexed map into a multidimensional list.
+
+  ## Example
+
+      iex> matrix = %{0 => %{0 => "x", 1 => "o", 2 => "x"}}
+      ...> Matrix.to_list(matrix)
+      [["x", "o", "x"]]
+  """
+  def to_list(matrix) when is_map(matrix) do
+    do_to_list(matrix)
+  end
+
+  defp do_to_list(matrix) when is_map(matrix) do
+    for {_index, value} <- matrix,
+        into: [],
+        do: do_to_list(value)
+  end
+
+  defp do_to_list(other), do: other
+end

2021/Day5/test.txt

@@ -0,0 +1,10 @@
+0,9 -> 5,9
+8,0 -> 0,8
+9,4 -> 3,4
+2,2 -> 2,1
+7,0 -> 7,4
+6,4 -> 2,0
+0,9 -> 2,9
+3,4 -> 1,4
+0,0 -> 8,8
+5,5 -> 8,2