2023 day 3

lib/2023_day3.exs

@@ -0,0 +1,54 @@
+contains_symbol = fn s ->
+  match = Regex.match?(~r/[^\d.]/, s)
+  match
+end
+
+grab_numbers = fn line ->
+  Regex.scan(~r/\d+/, line, return: :index)
+  |> Enum.map(fn [{index, len}] ->
+    {index, len, line |> String.slice(index, len) |> Integer.parse() |> elem(0)}
+  end)
+end
+
+part1 = fn s ->
+  for [pre, curr, post] <-
+        s
+        |> Enum.reject(&(String.length(&1) == 0))
+        |> then(fn x -> Enum.concat([""], x) end)
+        |> Enum.chunk(3, 1)
+        |> Enum.map(fn u -> Enum.map(u, &String.trim/1) end),
+      [{index, length}] <- Regex.scan(~r/\d+/, curr, return: :index),
+      contains_symbol.(String.slice(curr, max(index - 1, 0), length + 2)) ||
+        contains_symbol.(String.slice(pre, max(index - 1, 0), length + 2)) ||
+        contains_symbol.(String.slice(post, max(index - 1, 0), length + 2)),
+      {number, _} = String.slice(curr, index, length) |> Integer.parse() do
+    number
+  end
+  |> Enum.sum()
+end
+
+part2 = fn s ->
+  for [pre, curr, post] <-
+        s
+        |> Enum.reject(&(String.length(&1) == 0))
+        |> then(fn x -> Enum.concat([""], x) end)
+        |> then(fn x -> Enum.concat(x, [""]) end)
+        |> Enum.chunk(3, 1)
+        |> Enum.map(fn u -> Enum.map(u, &String.trim/1) end),
+      curr |> String.contains?("*"),
+      [{gear_idx, _}] <- Regex.scan(~r/\*/, curr, return: :index),
+      matches =
+        grab_numbers.(pre) |> Enum.concat(grab_numbers.(post)) |> Enum.concat(grab_numbers.(curr)),
+      valid_matches =
+        matches
+        |> Enum.filter(fn {m_idx, m_len, _} ->
+          gear_idx in max(0, m_idx - 1)..(m_idx + m_len)
+        end),
+      valid_matches |> Enum.count() == 2,
+      [{_, _, a}, {_, _, b}] = valid_matches do
+    a * b
+  end
+  |> Enum.sum()
+end
+
+part2.(IO.stream()) |> IO.puts()