Mixifying

lib/advent_of_code.ex

@@ -0,0 +1,18 @@
+defmodule AdventOfCode do
+  @moduledoc """
+  Documentation for `AdventOfCode`.
+  """
+
+  @doc """
+  Hello world.
+
+  ## Examples
+
+      iex> AdventOfCode.hello()
+      :world
+
+  """
+  def hello do
+    :world
+  end
+end

lib/year_2025/day1.exs

@@ -0,0 +1,8 @@
+filepath = Path.join([File.cwd!, "lib", "year_2025", "day1_input.txt"])
+ops = File.stream!(filepath)
+|>Stream.map(&String.trim_trailing/1)
+|>Enum.to_list
+
+{_, zeroes} = AdventOfCode.Year2025.Dial.rotate(ops)
+IO.puts(zeroes)
+

lib/year_2025/dial.ex

@@ -0,0 +1,38 @@
+defmodule AdventOfCode.Year2025.Dial do
+  # Initial conditions
+  def rotate(operations), do: rotate(50, operations, 0)
+
+  # When no operations remain, return the number of zeroes
+  def rotate(index, [], zeroes), do: { index, zeroes }
+
+  # Compute the new dial position
+  def rotate(index, [head | tail], zeroes) do
+    { new_index, _crosses } = case head do
+      "R" <> number -> rotate_right(index, String.to_integer(number))
+      "L" <> number -> rotate_left(index, String.to_integer(number))
+    end
+
+    case new_index do
+      0 -> rotate(new_index, tail, zeroes+1)
+      _ -> rotate(new_index, tail, zeroes)
+    end
+  end
+
+  defp rotate_right(index, number) do
+    crosses = div(number, 100)
+    diff = index + rem(number, 100)
+    case diff do
+      diff when diff <= 99 -> { diff, crosses }
+      diff when diff > 99 -> { diff - 100, crosses + 1 }
+    end
+  end
+
+  defp rotate_left(index, number) do
+    crosses = div(number, 100)
+    diff = index - rem(number, 100)
+    case diff do
+      diff when diff >= 0 -> { diff, crosses }
+      diff when diff < 0 -> { diff + 100, crosses + 1 }
+    end
+  end
+end