day 6 part 1 elixir

Author: maco

elixir/2024/lib/advent_of_code/day_06.ex

@@ -1,7 +1,74 @@
 defmodule AdventOfCode.Day06 do
-  def part1(_args) do
+  import AdventOfCode.Parsing
+
+  def part1(input) do
+    grid = parse_grid(input)
+    start = find_start(grid)
+    vector = {-1, 0}
+    seen = go(grid, start, vector, MapSet.new())
+    Enum.count(seen)
   end
 
   def part2(_args) do
   end
+
+  defp go(grid, position, vector, seen) do
+    seen = MapSet.put(seen, position)
+
+    case look(grid, position, vector) do
+      {_, nil} ->
+        seen
+
+      {_new_pos, "#"} ->
+        new_vector = turn(vector)
+        go(grid, position, new_vector, seen)
+
+      {new_pos, _} ->
+        go(grid, new_pos, vector, seen)
+    end
+  end
+
+  defp turn({-1, 0}), do: {0, 1}
+  defp turn({0, 1}), do: {1, 0}
+  defp turn({1, 0}), do: {0, -1}
+  defp turn({0, -1}), do: {-1, 0}
+
+  defp look(grid, pos, vector) do
+    new_pos = calculate_move(pos, vector)
+    val = Map.get(grid, new_pos)
+    {new_pos, val}
+  end
+
+  defp calculate_move({row, col}, {row_dir, col_dir}), do: {row + row_dir, col + col_dir}
+
+  defp find_start(grid) do
+    {key, _val} = Enum.find(grid, fn {_key, val} -> val == "^" end)
+    key
+  end
+
+  def show_grid(grid, label) do
+    IO.puts(label)
+    keys = Map.keys(grid) |> Enum.sort()
+
+    for {_row, col} = k <- keys do
+      if col == 0 do
+        IO.write("\n")
+      end
+
+      Map.get(grid, k, "*") |> IO.write()
+    end
+
+    Enum.reduce(keys, [], fn
+      {_row, 0}, acc ->
+        Enum.reverse(acc) |> Enum.join("") |> IO.write()
+        IO.write("\n")
+        []
+
+      k, acc ->
+        [Map.get(grid, k, "*") | acc]
+    end)
+
+    IO.puts("\n")
+    grid
+  end
 end

elixir/2024/test/advent_of_code/day_06_test.exs

@@ -3,12 +3,20 @@ defmodule AdventOfCode.Day06Test do
 
   import AdventOfCode.Day06
 
-  @tag :skip
   test "part1" do
-    input = nil
-    result = part1(input)
-
-    assert result
+    input = """
+    ....#.....
+    .........#
+    ..........
+    ..#.......
+    .......#..
+    ..........
+    .#..^.....
+    ........#.
+    #.........
+    ......#...
+    """
+    41 = part1(input)
   end
 
   @tag :skip