Day 13

lib/day13.ex

@@ -0,0 +1,46 @@
+defmodule Aoc2023.Day13 do
+  use Aoc2023
+
+  def parse(input) do
+    input
+    |> String.split("\n\n")
+    |> Enum.map(pipe(lines |> Enum.map(&String.to_charlist/1)))
+  end
+
+  defp reflected_row(block, smudges) do
+    0..(length(block) - 2)
+    |> Enum.filter(fn i ->
+      Enum.zip_with(
+        Enum.take(block, i + 1) |> Enum.reverse() |> Enum.concat(),
+        Enum.drop(block, i + 1) |> Enum.concat(),
+        &Kernel.==/2
+      )
+      |> Enum.count(&(not &1))
+      |> Kernel.==(smudges)
+    end)
+    |> head
+  end
+
+  defp reflected_column(block, smudges) do
+    block |> transpose() |> reflected_row(smudges)
+  end
+
+  defp reflection(block, smudges \\ 0) do
+    row = reflected_row(block, smudges)
+    if row != nil, do: {:h, row + 1}, else: {:v, reflected_column(block, smudges) + 1}
+  end
+
+  def part1(input) do
+    reflections = input |> Enum.map(&reflection/1)
+
+    (Keyword.get_values(reflections, :h) |> Enum.sum()) * 100 +
+      (Keyword.get_values(reflections, :v) |> Enum.sum())
+  end
+
+  def part2(input) do
+    reflections = input |> Enum.map(pipe(reflection(1)))
+
+    (Keyword.get_values(reflections, :h) |> Enum.sum()) * 100 +
+      (Keyword.get_values(reflections, :v) |> Enum.sum())
+  end
+end