add 2024 day 3

elixir/livebook/2024/day3.livemd

@@ -0,0 +1,33 @@
+# AOC 2024 Day 3
+
+## Section
+
+```elixir
+input = File.read!("/data/input.txt")
+```
+
+```elixir
+Regex.scan(
+  ~r/mul\((\d+),(\d+)\)/,
+  input
+)
+|> Stream.map(fn [_, a, b] -> String.to_integer(a) * String.to_integer(b) end)
+|> Enum.sum()
+```
+
+```elixir
+for instruction <- Regex.scan(
+  ~r/(mul\((\d+),(\d+)\)|don't\(\)|do\(\))/,
+  input
+), reduce: {true, 0} do
+  {enabled?, acc} ->
+    (fn
+      false, ["mul" <> _ | _] -> {false, acc}
+      true, ["mul" <> _, _, a, b] -> {true, acc + String.to_integer(a) * String.to_integer(b)}
+      _, ["don" <> _ | _] -> {false, acc}
+      _, ["do()" | _] -> {true, acc}
+    end
+    ).(enabled?, instruction)
+end
+```
+