diff --git a/lib/day3.ex b/lib/day3.ex
new file mode 100644
index 0000000..befc7ab
--- /dev/null
+++ b/lib/day3.ex
@@ -0,0 +1,40 @@
+defmodule Day3 do
+  def init_state(part) do
+    %{sum: 0, part: part}
+  end
+
+  defp find_duplicates(line) do
+    line |>
+      String.to_charlist() |>
+      Enum.chunk_every(Integer.floor_div(String.length(line), 2)) |>
+      Enum.map(&MapSet.new/1) |>
+      then(fn [a,b] -> MapSet.intersection(a,b) end) |>
+      MapSet.to_list()
+  end
+
+  defp to_priority(c) do
+    u = if is_nil(c) do 0 else if c < 97 do c - 38 else c - 96 end end
+    u
+  end
+
+  def execute(line, state) do
+    increment_sum = fn s -> Map.update(state, :sum, 0, &(&1 + s)) end 
+
+    trimmed = line |> String.trim()
+
+    unless String.length(trimmed) == 0 do
+      trimmed |>
+        find_duplicates() |>
+        Enum.map(&to_priority(&1)) |>
+        Enum.reduce(&(&1 + &2)) |>
+        increment_sum.()
+    else
+      state
+    end
+  end
+
+  def get_answer(state) do
+    state.sum
+  end
+end
+
diff --git a/main.exs b/main.exs
index 98fd10b..a5598de 100644
--- a/main.exs
+++ b/main.exs
@@ -1 +1 @@
-AOCRunner.run(Day2, :part2)
+AOCRunner.run(Day3, :part1)