Solve day 3

lib/aoc2024/day_03.ex

@@ -1,13 +1,26 @@
 defmodule Aoc2024.Day03 do
-  def parse(input) do
-    input |> String.split("\n", trim: true)
+  def part1(instructions) do
+    ~r/mul\(([0-9]+),([0-9]+)\)/
+    |> Regex.scan(instructions)
+    |> Enum.map(fn [_all, num1_str, num2_str] ->
+      case {Integer.parse(num1_str), Integer.parse(num2_str)} do
+        {{num1, ""}, {num2, ""}} -> num1 * num2
+        _ -> 0
+      end
+    end)
+    |> Enum.sum()
   end
 
-  def part1(_lines) do
-    :todo1
-  end
+  def part2(instructions) do
+    conditional_instructions =
+      ~r/don't\(\).*?do\(\)/s
+      |> Regex.replace(instructions, "|")
 
-  def part2(_lines) do
-    :todo2
+    # handle possible case where the instructions end with don't() and more mul
+    conditional_instructions2 =
+      ~r/don't\(\).*$/s
+      |> Regex.replace(conditional_instructions, "|")
+
+    part1(conditional_instructions2)
   end
 end

test/aoc2024_test.exs

@@ -31,4 +31,24 @@ defmodule Aoc2024Test do
     assert Aoc2024.Day02.part1(parsed_input) == 2
     assert Aoc2024.Day02.part2(parsed_input) == 4
   end
+
+  test "Day 3 - part 1" do
+    input = "xmul(2,4)%&mul[3,7]!@^do_not_mul(5,5)+mul(32,64]then(mul(11,8)mul(8,5))"
+    assert Aoc2024.Day03.part1(input) == 161
+  end
+
+  test "Day 3 - part 2" do
+    input = "xmul(2,4)&mul[3,7]!^don't()_mul(5,5)+mul(32,64](mul(11,8)undo()?mul(8,5))"
+    assert Aoc2024.Day03.part2(input) == 48
+  end
+
+  test "Day 3 - part 2 – end with don't" do
+    input = "xmul(2,4)&mul[3,7]!^don't()_mul(5,5)+mul(32,64](mul(11,8)un?mul(8,5))"
+    assert Aoc2024.Day03.part2(input) == 8
+  end
+
+  test "Day 3 - part 2 – support newlines within don't()...do() blocks" do
+    input = "xmul(2,4)&mul[3,7]!^don't()_mul(5,5)\n+mul(32,64](mul(11,8)undo()?mul(8,5))"
+    assert Aoc2024.Day03.part2(input) == 48
+  end
 end