From ac02740e85877cecd476efca1f39ad4f6503860e Mon Sep 17 00:00:00 2001
From: sloane <git@sloanelybutsurely.com>
Date: Wed, 11 Dec 2024 09:03:05 -0500
Subject: [PATCH] solve 2024 day 10

---
 2024/README.md      |  3 +-
 2024/lib/2024/10.ex | 84 +++++++++++++++++++++++++++++++++++++++++++++
 README.md           |  4 +--
 3 files changed, 88 insertions(+), 3 deletions(-)
 create mode 100644 2024/lib/2024/10.ex

diff --git a/2024/README.md b/2024/README.md
index 316419d..12a9c72 100644
--- a/2024/README.md
+++ b/2024/README.md
@@ -3,7 +3,7 @@
 |  S  |  M  |  T  |  W  |  T  |  F  |  S  |
 | :-: | :-: | :-: | :-: | :-: | :-: | :-: |
 | [1] | [2] | [3] | [4] | [5] | [6] | [7] |
-| [8] | [9] |  10 |  11 |  12 |  13 |  14 |
+| [8] | [9] | [10]|  11 |  12 |  13 |  14 |
 |  15 |  16 |  17 |  18 |  19 |  20 |  21 |
 |  22 |  23 |  24 |  25 |     |     |     |
 
@@ -16,3 +16,4 @@
 [7]: ./lib/2024/7.ex
 [8]: ./lib/2024/8.ex
 [9]: ./lib/2024/9.ex
+[10]: ./lib/2024/10.ex
diff --git a/2024/lib/2024/10.ex b/2024/lib/2024/10.ex
new file mode 100644
index 0000000..caaaadd
--- /dev/null
+++ b/2024/lib/2024/10.ex
@@ -0,0 +1,84 @@
+import AOC
+import AOC.Prelude
+
+aoc 2024, 10 do
+  def p1(input) do
+    map = read_map(input)
+
+    trailheads = map |> Map.filter(&match?({_, 0}, &1)) |> Map.keys()
+
+    trailheads
+    |> Enum.map(&score(&1, map))
+    |> Enum.sum()
+  end
+
+  def p2(input) do
+    map = read_map(input)
+
+    trailheads = map |> Map.filter(&match?({_, 0}, &1)) |> Map.keys()
+
+    trailheads
+    |> Enum.map(&rating(&1, map))
+    |> Enum.sum()
+  end
+
+  ## part 1
+
+  defp score(pos, map) do
+    pos
+    |> reachable_nines(map, MapSet.new())
+    |> Enum.count()
+  end
+
+  defp reachable_nines(pos, map, seen) do
+    seen = MapSet.put(seen, pos)
+    curr = Map.get(map, pos)
+
+    if curr == 9 do
+      [pos]
+    else
+      [&n/1, &s/1, &e/1, &w/1]
+      |> Enum.map(& &1.(pos))
+      |> Enum.reject(&MapSet.member?(seen, &1))
+      |> Enum.filter(&(Map.get(map, &1, 0) == curr + 1))
+      |> Enum.flat_map(&reachable_nines(&1, map, seen))
+      |> Enum.uniq()
+    end
+  end
+
+  ## part 2
+
+  defp rating(pos, map, seen \\ MapSet.new()) do
+    seen = MapSet.put(seen, pos)
+    curr = Map.get(map, pos)
+
+    if curr == 9 do
+      1
+    else
+      [&n/1, &s/1, &e/1, &w/1]
+      |> Enum.map(& &1.(pos))
+      |> Enum.reject(&MapSet.member?(seen, &1))
+      |> Enum.filter(&(Map.get(map, &1, 0) == curr + 1))
+      |> Enum.map(&rating(&1, map, seen))
+      |> Enum.sum()
+    end
+  end
+
+  ## shared
+
+  defp n({x, y}), do: {x, y + 1}
+  defp s({x, y}), do: {x, y - 1}
+  defp e({x, y}), do: {x + 1, y}
+  defp w({x, y}), do: {x - 1, y}
+
+  ## input
+
+  def read_map(input) do
+    input
+    |> map_grid()
+    |> Enum.reject(&match?({_, "."}, &1))
+    |> Map.new(fn
+      {k, v} -> {k, String.to_integer(v)}
+    end)
+  end
+end
diff --git a/README.md b/README.md
index b3b4d49..1ed3b9c 100644
--- a/README.md
+++ b/README.md
@@ -15,8 +15,8 @@
 | [2021] | **43/50** 🌟 | Elixir |
 | [2022] | **14/50** 🌟 | Elixir, Haskell |
 | [2023] | **19/50** 🌟 | Elixir, Haskell |
-| [2024] | **18/50** 🌟 | Elixir |
-| **Total** | **174** 🌟| |
+| [2024] | **20/50** 🌟 | Elixir |
+| **Total** | **176** 🌟| |
 
 [2015]: ./2015
 [2017]: ./2017