Day 5. Switched from Roc to Elixir. The compiler hasn\'t crashed once yet!

day5/main.exs

@@ -0,0 +1,55 @@
+defmodule Day5 do
+  def run do
+    {rules, updates} = parseFile("data.txt")
+
+    {validUpdates, invalidUpdates} = Enum.split_with(updates, &updateValid?(&1, rules))
+
+    validMiddles = Enum.map(validUpdates, &middleDigit/1)
+    IO.puts("Part 1: #{Enum.sum(validMiddles)}")
+
+    # sort the invalid ones with a custom sorter that looks for [a, b] in the rules list. if [a, b] exists, sort a before b
+    invalidSorted =
+      Enum.map(invalidUpdates, fn update ->
+        Enum.sort(update, fn first, second ->
+          Enum.member?(rules, [first, second])
+        end)
+      end)
+
+    invalidMiddles = Enum.map(invalidSorted, &middleDigit/1)
+    IO.puts("Part 2: #{Enum.sum(invalidMiddles)}")
+  end
+
+  defp parseFile(file) do
+    [topSection, bottomSection] = File.read!(file) |> String.split("\n\n")
+
+    rules = String.split(topSection, "\n") |> Enum.map(fn l -> String.split(l, "|") end)
+
+    updates =
+      String.split(bottomSection, "\n")
+      |> Enum.drop(-1)
+      |> Enum.map(fn l -> String.split(l, ",") end)
+
+    {rules, updates}
+  end
+
+  defp updateValid?(update, rules) do
+    Enum.reduce_while(rules, true, fn [left, right], acc ->
+      # if it doesn't contain both, or it does and they're in the right order
+      if !(Enum.member?(update, left) and Enum.member?(update, right)) or
+           Enum.find_index(update, &(&1 == left)) < Enum.find_index(update, &(&1 == right)) do
+        # continue and try the next one
+        {:cont, acc}
+      else
+        # otherwise halt the reduction, this update is invalid
+        {:halt, false}
+      end
+    end)
+  end
+
+  defp middleDigit(update) do
+    middle = trunc(length(update) / 2)
+    String.to_integer(Enum.at(update, middle))
+  end
+end
+
+Day5.run()

day5/test.txt

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+47|53
+97|13
+97|61
+97|47
+75|29
+61|13
+75|53
+29|13
+97|29
+53|29
+61|53
+97|53
+61|29
+47|13
+75|47
+97|75
+47|61
+75|61
+47|29
+75|13
+53|13
+
+75,47,61,53,29
+97,61,53,29,13
+75,29,13
+75,97,47,61,53
+61,13,29
+97,13,75,29,47