From c735ab61c7d3af7b91ace22d41e4c3467f0cff2f Mon Sep 17 00:00:00 2001
From: Doruk Gurleyen <doruk.gurleyen@divvypay.com>
Date: Sun, 12 Dec 2021 01:38:16 -0600
Subject: [PATCH] 2021.12

---
 challenges/2021/12.exs        | 72 +++++++++++++++++++++++++++++++++++
 challenges/2021/12.js         | 61 +++++++++++++++++++++++++++++
 challenges/2021/inputs/12.txt | 23 +++++++++++
 3 files changed, 156 insertions(+)
 create mode 100644 challenges/2021/12.exs
 create mode 100644 challenges/2021/12.js
 create mode 100644 challenges/2021/inputs/12.txt

diff --git a/challenges/2021/12.exs b/challenges/2021/12.exs
new file mode 100644
index 0000000..e2a821b
--- /dev/null
+++ b/challenges/2021/12.exs
@@ -0,0 +1,72 @@
+Code.compile_file(Path.join([__ENV__.file], ["../../../utils/utils.exs"]))
+
+defmodule Challenge do
+  @moduledoc false
+
+  def first_result(input) do
+    input
+    |> parse_input
+    |> build_cave_states
+    |> explore("start")
+  end
+
+  def second_result(input) do
+    input
+    |> parse_input
+    |> build_cave_states
+    |> explore("start", 2)
+  end
+
+  defp explore(states, cave, max_sm_cave_visits \\ 1, seen_sm_cave \\ false)
+  defp explore(_states, "end", _max_sm_cave_visits, _seen_sm_cave), do: 1
+
+  defp explore(states, cave, max_sm_cave_visits, seen_sm_cave) do
+    {adjacencies, visited} = Map.get(states, cave)
+
+    cave
+    |> updated_visited_count(visited, seen_sm_cave, max_sm_cave_visits)
+    |> case do
+      nil ->
+        0
+
+      new_visited_count ->
+        updated_states = Map.put(states, cave, {adjacencies, new_visited_count})
+
+        Enum.reduce(
+          adjacencies,
+          0,
+          &(&2 + explore(updated_states, &1, max_sm_cave_visits, seen_sm_cave || visited > 0))
+        )
+    end
+  end
+
+  defp updated_visited_count(cave, seen_count, seen_sm_cave, max_sm_cave_visits \\ 1)
+  defp updated_visited_count(_cave, 1, _, 1), do: nil
+  defp updated_visited_count(_cave, 2, _seen_sm_cave, 2), do: nil
+  defp updated_visited_count(_cave, 1, true, 2), do: nil
+
+  defp updated_visited_count(cave, seen_count, _seen_sm_cave, _max_sm_cave_visits),
+    do: if(String.downcase(cave) == cave, do: seen_count + 1, else: 0)
+
+  defp build_cave_states(adjacencies) do
+    Enum.reduce(adjacencies, %{}, fn [left, right], acc ->
+      left_state = Map.get(acc, left, {[], 0})
+      right_state = Map.get(acc, right, {[], 0})
+
+      updated_left_state = maybe_add_to_adjacencies(right, left_state)
+      updated_right_state = maybe_add_to_adjacencies(left, right_state)
+
+      acc
+      |> Map.put(left, updated_left_state)
+      |> Map.put(right, updated_right_state)
+    end)
+  end
+
+  defp maybe_add_to_adjacencies("start", state), do: state
+  defp maybe_add_to_adjacencies(cave, state), do: {[cave | elem(state, 0)], elem(state, 1)}
+
+  defp parse_input(input), do: Enum.map(input, &String.split(&1, "-"))
+end
+
+Utils.run(&Challenge.first_result/1, __ENV__.file, "Q1")
+Utils.run(&Challenge.second_result/1, __ENV__.file, "Q2")
diff --git a/challenges/2021/12.js b/challenges/2021/12.js
new file mode 100644
index 0000000..11d325c
--- /dev/null
+++ b/challenges/2021/12.js
@@ -0,0 +1,61 @@
+// Part 1
+const solvePuzzle1 = (input) => {
+  const caveStates = buildCaveStates(parseInput(input));
+  const getIncrementVisitedBy = (cave, visited) => {
+    if (visited) return null;
+    if (cave.toLowerCase() === cave) return 1;
+    return 0;
+  };
+  return explore("start", caveStates, getIncrementVisitedBy);
+};
+
+// Part 2
+const solvePuzzle2 = (input) => {
+  const caveStates = buildCaveStates(parseInput(input));
+  const getIncrementVisitedBy = (cave, visitedCount, visitedSmallCave) => {
+    if (visitedCount === 2 || (visitedCount === 1 && visitedSmallCave)) return null;
+    if (cave.toLowerCase() === cave) return 1;
+    return 0;
+  };
+  return explore("start", caveStates, getIncrementVisitedBy);
+};
+
+const addCaveToAdjacencies = (cave, state) => {
+  if (!state) return null;
+  cave !== "start" && state[0].push(cave);
+  return state;
+};
+
+const buildCaveStates = (input) => {
+  const caveStates = new Map();
+  for (let [left, right] of input) {
+    addCaveToAdjacencies(right, caveStates.get(left)) || caveStates.set(left, createCaveState(right));
+    addCaveToAdjacencies(left, caveStates.get(right)) || caveStates.set(right, createCaveState(left));
+  }
+  return caveStates;
+};
+
+const createCaveState = (cave) => (cave !== "start" ? [[cave], 0] : [[], 0]);
+
+const explore = (cave, caveStates, getIncrementVisitedBy, visitedSmallCave = false) => {
+  if (cave === "end") return 1;
+
+  const stateOfTheCave = caveStates.get(cave);
+  const [adjacencies, visited] = stateOfTheCave;
+  const incrementVisitedBy = getIncrementVisitedBy(cave, visited, visitedSmallCave);
+
+  if (incrementVisitedBy == null) return 0;
+  stateOfTheCave[1] += incrementVisitedBy;
+
+  const pathsFound = adjacencies.reduce(
+    (acc, val) => acc + explore(val, caveStates, getIncrementVisitedBy, visitedSmallCave || visited),
+    0
+  );
+  stateOfTheCave[1] -= incrementVisitedBy;
+  return pathsFound;
+};
+
+const parseInput = (input) => input.split("\n").map((l) => l.split("-"));
+
+require(__dirname + "/../../utils/test.js").test(__filename, __dirname, solvePuzzle1);
+require(__dirname + "/../../utils/test.js").test(__filename, __dirname, solvePuzzle2);
diff --git a/challenges/2021/inputs/12.txt b/challenges/2021/inputs/12.txt
new file mode 100644
index 0000000..c9a63b5
--- /dev/null
+++ b/challenges/2021/inputs/12.txt
@@ -0,0 +1,23 @@
+pn-TY
+rp-ka
+az-aw
+al-IV
+pn-co
+end-rp
+aw-TY
+rp-pn
+al-rp
+end-al
+IV-co
+end-TM
+co-TY
+TY-ka
+aw-pn
+aw-IV
+pn-IV
+IV-ka
+TM-rp
+aw-PD
+start-IV
+start-co
+start-pn
\ No newline at end of file