solve 2023 8.1

2023/README.md

@@ -3,7 +3,7 @@
 |  S  |  M  |  T  |  W  |  T  |  F  |  S  |
 | :-: | :-: | :-: | :-: | :-: | :-: | :-: |
 |     |     |     |     |     | [1] | [2] |
-| [3] | [4] | [5] |  6  | [7] |  8  |  9  |
+| [3] | [4] | [5] |  6  | [7] | [8] |  9  |
 | 10  | 11  | 12  | 13  | 14  | 15  | 16  |
 | 17  | 18  | 19  | 20  | 21  | 22  | 23  |
 | 24  | 25  |     |     |     |     |     |
@@ -16,3 +16,4 @@
 [5]: ./lib/2023/5.ex
 <!-- [6]: ./lib/2023/6.ex -->
 [7]: ./lib/2023/7.ex
+[8]: ./lib/2023/8.ex

2023/lib/2023/8.ex

@@ -0,0 +1,51 @@
+import AOC
+import AOCHelpers
+
+aoc 2023, 8 do
+  def p1(input) do
+    {instructions, mappings} = read_input(input)
+
+    start = "AAA"
+    finish = "ZZZ"
+
+    all_but_last_step =
+      instructions
+      |> Stream.cycle()
+      |> Stream.scan(start, &step(&1, &2, mappings))
+      |> Stream.take_while(&(&1 != finish))
+      |> Enum.count()
+
+    all_but_last_step + 1
+  end
+
+  def p2(_input) do
+  end
+
+  def step("L", curr, mappings) do
+    mappings
+    |> Map.get(curr)
+    |> elem(0)
+  end
+
+  def step("R", curr, mappings) do
+    mappings
+    |> Map.get(curr)
+    |> elem(1)
+  end
+
+  def read_input(input) do
+    [instructions_string, _ | mapping_lines] = lines(input)
+    instructions = letters(instructions_string)
+
+    mappings =
+      mapping_lines
+      |> Enum.map(fn mapping_line ->
+        [_, key, left, right] = Regex.run(~r/^(.+) = \((.+), (.+)\)$/, mapping_line)
+
+        {key, {left, right}}
+      end)
+      |> Enum.into(%{})
+
+    {instructions, mappings}
+  end
+end

README.md

@@ -14,7 +14,7 @@
 1. [2020] **17/50** 🌟
 1. [2021] **43/50** 🌟
 1. [2022] **14/50** 🌟
-1. [2023] **11/50** 🌟
+1. [2023] **12/50** 🌟
 
 [2015]: ./2015
 [2017]: ./2017