day8

Author: akdemironur

08/sample_input

@@ -0,0 +1,10 @@
+LR
+
+11A = (11B, XXX)
+11B = (XXX, 11Z)
+11Z = (11B, XXX)
+22A = (22B, XXX)
+22B = (22C, 22C)
+22C = (22Z, 22Z)
+22Z = (22B, 22B)
+XXX = (XXX, XXX)

08/sol.exs

@@ -0,0 +1,50 @@
+defmodule Day08 do
+  defp read_input(file_path) do
+    case File.read(file_path) do
+      {:ok, content} ->
+        [directives | network_lines] =
+          content
+          |> String.split(~r/\n/, trim: true)
+
+        {directives |> String.graphemes(), network_lines |> Enum.map(&parse/1) |> Map.new()}
+
+      {:error, reason} ->
+        raise "Oh no! #{reason}"
+    end
+  end
+
+  defp parse(line) do
+    [_, from, left, right] = Regex.run(~r/(\w+) = \((\w+), (\w+)\)/, line)
+    {from, %{"L" => left, "R" => right}}
+  end
+
+  defp resolve(from, target, network, [], dir, acc),
+    do: resolve(from, target, network, dir, dir, acc)
+
+  defp resolve(from, target, network, [dir | rest], directives_all, acc) do
+    if String.match?(from, target) do
+      acc
+    else
+      resolve(network[from][dir], target, network, rest, directives_all, acc + 1)
+    end
+  end
+
+  def partA(file_path) do
+    {directives, network} = read_input(file_path)
+    resolve("AAA", ~r/ZZZ/, network, directives, directives, 0)
+  end
+
+  def partB(file_path) do
+    {directives, network} = read_input(file_path)
+
+    Map.keys(network)
+    |> Enum.filter(fn str -> String.ends_with?(str, "A") end)
+    |> Enum.map(fn str ->
+      resolve(str, ~r/Z\z/, network, directives, directives, 0)
+    end)
+    |> Enum.reduce(fn x, y -> div(x * y, Integer.gcd(x, y)) end)
+  end
+end
+
+IO.puts(Day08.partA("./input"))
+IO.puts(Day08.partB("./input"))