solve 2024 day 5

2024/README.md

@@ -2,7 +2,7 @@
 
 |  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 |     |     |     |
@@ -11,3 +11,4 @@
 [2]: ./lib/2024/2.ex
 [3]: ./lib/2024/3.ex
 [4]: ./lib/2024/4.ex
+[5]: ./lib/2024/5.ex

2024/lib/2024/5.ex

@@ -0,0 +1,67 @@
+import AOC
+
+aoc 2024, 5 do
+  def p1(input) do
+    {rules, updates} = parse_input(input)
+
+    updates
+    |> Enum.filter(&sorted?(&1, rules))
+    |> Enum.map(&median/1)
+    |> Enum.sum()
+  end
+
+  def p2(input) do
+    {rules, updates} = parse_input(input)
+
+    updates
+    |> Enum.reject(&sorted?(&1, rules))
+    |> Enum.map(fn update ->
+      Enum.sort(update, &sort_update(&1, &2, rules))
+    end)
+    |> Enum.map(&median/1)
+    |> Enum.sum()
+  end
+
+  def sorted?(update, rules) do
+    update == Enum.sort(update, &sort_update(&1, &2, rules))
+  end
+
+  def median(update) do
+    Enum.at(update, div(length(update), 2))
+  end
+
+  def sort_update(a, b, rules) do
+    a_before = Map.get(rules, a, [])
+    b in a_before
+  end
+
+  ## input parsing
+
+  def parse_input(input) do
+    [rules_str, updates_str] = String.split(input, "\n\n")
+
+    rules = parse_rules(rules_str)
+    updates = parse_updates(updates_str)
+
+    {rules, updates}
+  end
+
+  def parse_rules(rules_str) do
+    rules_str
+    |> String.split("\n", trim: true)
+    |> Enum.group_by(
+      &String.to_integer(binary_part(&1, 0, 2)),
+      &String.to_integer(binary_part(&1, 3, 2))
+    )
+  end
+
+  def parse_updates(updates_str) do
+    updates_str
+    |> String.split("\n", trim: true)
+    |> Enum.map(fn line ->
+      line
+      |> String.split(",")
+      |> Enum.map(&String.to_integer/1)
+    end)
+  end
+end

README.md

@@ -15,8 +15,8 @@
 | [2021] | **43/50** 🌟 | Elixir |
 | [2022] | **14/50** 🌟 | Elixir, Haskell |
 | [2023] | **19/50** 🌟 | Elixir, Haskell |
-| [2024] | **8/50** 🌟  | Elixir |
+| [2024] | **10/50** 🌟 | Elixir |
-| **Total** | **162** 🌟 | |
+| **Total** | **162** 🌟| |
 
 [2015]: ./2015
 [2017]: ./2017