[WIP]: Day 12: Hill Climbing Algorithm -- AoC 22

stream =
  File.stream!("/Users/pw/src/weiland/adventofcode/2022/input/12.txt")
  |> Stream.map(&String.trim/1)

stream =
  "aabqponm
abcryxxl
accszExk
acctuvwj
abdefghi"
  |> String.split("\n")

Part One

reducer = fn {row, y}, acc ->
  new_row =
    row
    |> Enum.reduce(%{}, fn {value, x}, row_acc -> Map.put(row_acc, %{x: x, y: y}, value) end)

  acc
  |> Map.merge(new_row)
end

stream =
  stream
  |> Stream.map(&String.graphemes/1)
  |> Stream.map(&Enum.with_index/1)
  |> Stream.with_index()
  |> Enum.reduce(%{}, reducer)

# stream |> Enum.filter(fn {_key, value} -> value == "S" end)

defmodule Solution do
  def find_path(x, y, path, matrix) do
    current_value = Map.get(matrix, %{x: x, y: y})
    current_element = %{%{x: x, y: x} => current_value}

    if current_value == "E" do
      path
    end

    neighbours =
      get_neighbours(x, y, matrix)
      # only new neighbours
      |> Enum.filter(fn n -> !Enum.member?(path, n) end)

    if Kernel.length(neighbours) == 0 do
      :abort
    end

    neighbours
    |> Enum.map(fn %{x: x, y: y} -> find_path(x, y, [current_element | path], matrix) end)
    |> Enum.filter(fn n -> n != :abort end)
  end

  def get_neighbours(x, y, matrix) do
    current_value = Map.get(matrix, %{x: x, y: y})

    %{}
    |> Map.put(%{x: x - 1, y: y}, Map.get(matrix, %{x: x - 1, y: y}))
    |> Map.put(%{x: x + 1, y: y}, Map.get(matrix, %{x: x + 1, y: y}))
    |> Map.put(%{x: x, y: y - 1}, Map.get(matrix, %{x: x, y: y - 1}))
    |> Map.put(%{x: x, y: y + 1}, Map.get(matrix, %{x: x, y: y + 1}))
    |> Map.filter(fn {_key, value} -> value != nil end)
    |> Map.filter(fn {_key, value} -> value >= current_value != nil end)
    |> Map.to_list()
    |> Enum.map(fn {key, value} -> key end)
  end
end

Solution.find_path(0, 1, [%{x: 0, y: 0}], stream)

Part Two

stream
|> Enum.to_list()