Day07 and Day08 both parts

lib/aoc2024/day_08.ex

@@ -1,13 +1,80 @@
 defmodule Aoc2024.Day08 do
   def parse(input) do
-    input |> String.split("\n", trim: true)
+    input = input |> String.trim() |> String.split("\n") |> Enum.map(&String.codepoints/1)
+    w = Enum.count(Enum.at(input, 0))
+    h = Enum.count(input)
+
+    input =
+      walk(input, w, h)
+      |> Enum.reduce(%{}, fn {x, i, j}, m ->
+        if Map.has_key?(m, x) do
+          %{m | x => [{i, j} | m[x]]}
+        else
+          Map.put(m, x, [{i, j}])
+        end
+      end)
+
+    {input, w, h}
   end
 
-  def part1(_lines) do
-    :todo1
+  defp walk(t, w, h), do: walk(t, 0, 0, w, h, [])
+  defp walk(_t, i, _j, _w, h, towers) when i == h, do: towers
+  defp walk(t, i, j, w, h, towers) when j == w, do: walk(t, i + 1, 0, w, h, towers)
+
+  defp walk(t, i, j, w, h, towers) do
+    case t |> Enum.at(i) |> Enum.at(j) do
+      "." -> walk(t, i, j + 1, w, h, towers)
+      x -> walk(t, i, j + 1, w, h, [{x, i, j} | towers])
+    end
   end
 
-  def part2(_lines) do
-    :todo2
+  def part1({input, w, h}) do
+    for {_x, all} <- input do
+      Task.async(fn -> comb(&antinodes/4, all) end)
+    end
+    |> Enum.map(&Task.await/1)
+    |> List.flatten()
+    |> Enum.into(MapSet.new())
+    |> Enum.filter(fn {i, j} -> i >= 0 and j >= 0 and i < h and j < w end)
+    |> Enum.count()
+  end
+
+  defp comb(antinodes, [current | others]), do: comb(antinodes, others, current, others, [])
+  defp comb(_antinodes, [_], _, [], res), do: res
+
+  defp comb(antinodes, [current | others], _, [], res),
+    do: comb(antinodes, others, current, others, res)
+
+  defp comb(antinodes, others, {i1, j1} = current, [{i2, j2} | tail], res) do
+    comb(antinodes, others, current, tail, [antinodes.(i1, j1, i2, j2) | res])
+  end
+
+  defp antinodes(i1, j1, i2, j2) do
+    di = i2 - i1
+    dj = j2 - j1
+    [{i1 - di, j1 - dj}, {i2 + di, j2 + dj}]
+  end
+
+  def part2({input, w, h}) do
+    for {_x, all} <- input do
+      Task.async(fn -> comb(fn i1, j1, i2, j2 -> antinodes2(w, h, i1, j1, i2, j2) end, all) end)
+    end
+    |> Enum.map(&Task.await/1)
+    |> List.flatten()
+    |> Enum.into(MapSet.new())
+    |> Enum.count()
+  end
+
+  defp antinodes2(w, h, i1, j1, i2, j2) do
+    di = i2 - i1
+    dj = j2 - j1
+
+    Stream.iterate({i1, j1}, fn {i, j} -> {i + di, j + dj} end)
+    |> Stream.take_while(fn {i, j} -> i >= 0 and j >= 0 and i < h and j < w end)
+    |> Stream.concat(
+      Stream.iterate({i2, j2}, fn {i, j} -> {i - di, j - dj} end)
+      |> Stream.take_while(fn {i, j} -> i >= 0 and j >= 0 and i < h and j < w end)
+    )
+    |> Enum.into([])
   end
 end