day 3 haha

lib/day03.ex

@@ -0,0 +1,72 @@
+defmodule AdventOfCode.Day03 do
+  def part1() do
+    input = File.read!("./priv/day03.part1.txt")
+    regex = ~r/mul\((\d{1,3}),(\d{1,3})\)/
+    instructions = Regex.scan(regex, input)
+
+    Enum.reduce(instructions, 0, fn instruction, sum ->
+      [_, left, right] = instruction
+      left = String.to_integer(left)
+      right = String.to_integer(right)
+      sum + left * right
+    end)
+  end
+
+  def part2() do
+    input = File.read!("./priv/day03.part2.txt")
+
+    String.graphemes(input)
+    |> Enum.with_index()
+    |> Enum.reduce({0, true}, fn {letter, index}, {sum, enable_instruction} ->
+      case letter do
+        "m" ->
+          {_head, substr} = String.split_at(input, index)
+
+          case :binary.match(substr, ")") do
+            {position, _length} ->
+              instruction = String.slice(substr, 0, position + 1)
+
+              case String.length(instruction) <= 12 and
+                     Regex.scan(~r/mul\((\d{1,3}),(\d{1,3})\)/, instruction) do
+                [[_, left, right]] ->
+                  left = String.to_integer(left)
+                  right = String.to_integer(right)
+
+                  IO.inspect(instruction)
+                  IO.inspect(left)
+                  IO.inspect(right)
+                  IO.inspect(enable_instruction)
+
+                  case enable_instruction do
+                    true ->
+                      {sum + left * right, enable_instruction}
+
+                    false ->
+                      {sum, enable_instruction}
+                  end
+
+                _ ->
+                  {sum, enable_instruction}
+              end
+
+            :nomatch ->
+              {sum, enable_instruction}
+          end
+
+        "d" ->
+          substr = String.slice(input, index, String.length("don't()"))
+
+          cond do
+            substr == "don't()" ->
+              {sum, false}
+
+            String.starts_with?(substr, "do()") ->
+              {sum, true}
+          end
+
+        _ ->
+          {sum, enable_instruction}
+      end
+    end)
+  end
+end