Day 4

Mix.install([:kino])

Read Input

file_input = Kino.Input.file("Please Select Input File")

file_info = Kino.Input.read(file_input)
file_path = Kino.Input.file_path(file_info.file_ref)
contents = File.read!(file_path)

{grid, start_points} = contents
  |> String.split("\n")
  |> Enum.with_index()
  |> Enum.reduce({%{}, []}, fn({line, y}, {grid, start_points}) ->
    line
    |> String.graphemes()
    |> Enum.with_index()
    |> Enum.reduce({grid, start_points}, fn({char, x}, {grid, start_points}) ->
      cond do
        char == "X" ->
          {Map.put(grid, {x, y}, char), [{x, y} | start_points]}
        Enum.member?(["M", "A", "S"], char) ->
          {Map.put(grid, {x, y}, char), start_points}
        true ->
          {grid, start_points}
      end
    end)
  end)

defmodule GraphTraversal do
  @search_diffs [{1, 0}, {1, 1}, {0, 1}, {-1, 1}, {-1, 0}, {-1, -1}, {0, -1}, {1, -1}]
  
  def find_sequence(start_x, start_y, grid, sequence) do
    @search_diffs
    |> Enum.reduce(0, fn({dx, dy}, found) ->
      find_sequence(start_x, start_y, grid, sequence, dx, dy, found)
    end)
  end
  def find_sequence(_x, _y, _grid, [], _dx, _dy, found),
    do: found + 1
  def find_sequence(x, y, grid, [current | rest], dx, dy, found) do
    case Map.get(grid, {x, y}) do
      ^current -> find_sequence(x + dx, y + dy, grid, rest, dx, dy, found)
      _        -> found
    end
  end
end

GraphTraversal.find_sequence(9, 9, grid, ["X", "M", "A", "S"])

Part 1

start_points
|> Enum.reduce(0, fn({x, y}, found) ->
  found + GraphTraversal.find_sequence(x, y, grid, ["X", "M", "A", "S"])
end)

Part 2