solve 2024 day 2

2024/README.md

@@ -2,9 +2,10 @@
 
 |  S  |  M  |  T  |  W  |  T  |  F  |  S  |
 | :-: | :-: | :-: | :-: | :-: | :-: | :-: |
-| [1] |   2 |   3 |   4 |   5 |   6 |   7 |
+| [1] | [2] |   3 |   4 |   5 |   6 |   7 |
 |   8 |   9 |  10 |  11 |  12 |  13 |  14 |
 |  15 |  16 |  17 |  18 |  19 |  20 |  21 |
 |  22 |  23 |  24 |  25 |     |     |     |
 
 [1]: ./lib/2024/1.ex
+[2]: ./lib/2024/2.ex

2024/lib/2024/2.ex

@@ -0,0 +1,47 @@
+import AOC
+
+aoc 2024, 2 do
+  def p1(input) do
+    input
+    |> list_of_lists_of_numbers()
+    |> Enum.count(&safe?/1)
+  end
+
+  def p2(input) do
+    input
+    |> list_of_lists_of_numbers()
+    |> Enum.count(&safe_with_dampener?(&1))
+  end
+
+  defp list_of_lists_of_numbers(input) do
+    input
+    |> String.split("\n")
+    |> Enum.map(fn line ->
+      line
+      |> String.split()
+      |> Enum.map(&String.to_integer/1)
+    end)
+  end
+
+  defp safe?(report) do
+    diffs = differences(report)
+
+    Enum.all?(diffs, &(1 <= &1 and &1 <= 3)) or
+      Enum.all?(diffs, &(-3 <= &1 and &1 <= -1))
+  end
+
+  def safe_with_dampener?(report) do
+    reports_with_a_single_level_removed =
+      for i <- 0..(length(report) - 1) do
+        {head, [_ | tail]} = Enum.split(report, i)
+        head ++ tail
+      end
+
+    safe?(report) or
+      Enum.any?(reports_with_a_single_level_removed, &safe?/1)
+  end
+
+  defp differences([_ | rest] = list) do
+    Enum.zip_with(list, rest, &(&1 - &2))
+  end
+end

README.md

@@ -15,7 +15,7 @@
 | [2021] | **43/50** 🌟 | Elixir |
 | [2022] | **14/50** 🌟 | Elixir, Haskell |
 | [2023] | **19/50** 🌟 | Elixir, Haskell |
-| [2024] | **2/50** 🌟  | Elixir |
+| [2024] | **4/50** 🌟  | Elixir |
 
 [2015]: ./2015
 [2017]: ./2017