day 2 part 1

2021/README.md

@@ -14,7 +14,7 @@
 
 |  S  |  M  |  T  |  W  |  T  |  F  |  S  |
 | :-: | :-: | :-: | :-: | :-: | :-: | :-: |
-|     |     |     | [1] |  2  |  3  |  4  |
+|     |     |     | [1] | [2] |  3  |  4  |
 |  5  |  6  |  7  |  8  |  9  | 10  | 11  |
 | 12  | 13  | 14  | 15  | 16  | 17  | 18  |
 | 19  | 20  | 21  | 22  | 23  | 24  | 25  |
@@ -31,12 +31,14 @@ Run `mix help <task>` for details.
 
 ## [`AdventOfCode.PuzzleSolver`](./lib/advent_of_code/puzzle_solver.ex)
 
-A behaviour for a solution to a puzzle. Must define a `solve/2` callback.
+A behaviour for a solution to a puzzle. Must define a `solve[2] callback.
 
 ## [`AdventOfCode.PuzzleCase`](./test/support/puzzle_case.ex)
 
-Case template defining an `assert_solution/2` helper.
+Case template defining an `assert_solution[2] helper.
 
 <!-- links -->
 
 [1]: ./lib/advent_of_code/day01.ex
+
+[2]: ./lib/advent_of_code/day02.ex

2021/lib/advent_of_code/day02.ex

@@ -0,0 +1,52 @@
+defmodule AdventOfCode.Day02 do
+  @moduledoc """
+  Day 2
+  """
+end
+
+defmodule AdventOfCode.Day02.Part1 do
+  @moduledoc """
+  Day 2, Part 1
+  """
+
+  alias AdventOfCode.PuzzleSolver
+  use PuzzleSolver
+
+  import AdventOfCode.Day02, warn: false
+
+  @impl PuzzleSolver
+  def solve(input_stream) do
+    input_stream
+    |> Stream.map(&String.trim/1)
+    |> Stream.map(&parse_action/1)
+    |> Enum.reduce({0, 0}, &apply_action/2)
+    |> product()
+  end
+
+  defp parse_action("forward " <> v), do: {:forward, String.to_integer(v)}
+  defp parse_action("down " <> v), do: {:down, String.to_integer(v)}
+  defp parse_action("up " <> v), do: {:up, String.to_integer(v)}
+
+  defp apply_action({:forward, v}, {horiz, depth}), do: {horiz + v, depth}
+  defp apply_action({:down, v}, {horiz, depth}), do: {horiz, depth + v}
+  defp apply_action({:up, v}, {horiz, depth}), do: {horiz, depth - v}
+
+  defp product({x, y}), do: x * y
+end
+
+defmodule AdventOfCode.Day02.Part2 do
+  @moduledoc """
+  Day 2, Part 2
+  """
+
+  alias AdventOfCode.PuzzleSolver
+  use PuzzleSolver
+
+  import AdventOfCode.Day02, warn: false
+
+  @impl PuzzleSolver
+  def solve(_input_stream) do
+    :ok |> to_string()
+  end
+end
+

2021/test/advent_of_code/day02/part_1_test.exs

@@ -0,0 +1,16 @@
+defmodule AdventOfCode.Day02.Part1Test do
+  use AdventOfCode.PuzzleCase, module: AdventOfCode.Day02.Part1
+
+  test "returns the product of horizontal position and depth" do
+    input = ~S"""
+    forward 5
+    down 5
+    forward 8
+    up 3
+    down 8
+    forward 2
+    """
+
+    assert_solution(input, 150)
+  end
+end

2021/test/advent_of_code/day02/part_2_test.exs

@@ -0,0 +1,11 @@
+defmodule AdventOfCode.Day02.Part2Test do
+  use AdventOfCode.PuzzleCase, module: AdventOfCode.Day02.Part2
+
+  test "returns :ok" do
+    input = ~S"""
+    input
+    """
+
+    assert_solution(input, "ok")
+  end
+end