Day 09: Smoke Basin

Problem statement

Setup

Dependencies

Mix.install([
  {:nx, "~> 0.1.0-dev", github: "elixir-nx/nx", branch: "main", sparse: "nx"},
  {:kino, "~> 0.4.1"}
])

Input

input = Kino.Input.textarea("Paste your input here")

parse_line = fn line ->
  line
  |> String.graphemes()
  |> Enum.map(&String.to_integer/1)
end

heightmap =
  input
  |> Kino.Input.read()
  |> String.split()
  |> Enum.map(parse_line)
  |> Nx.tensor()

{rows, cols} = Nx.shape(heightmap)

Part 1

heightmap
|> Nx.window_reduce(10, {3, 3}, [padding: :same], fn n, m -> min(n, m) end)
|> Nx.equal(heightmap)
|> Nx.select(Nx.add(heightmap, 1), Nx.tensor(0))
|> IO.inspect(label: "low points:")
|> Nx.sum()
|> Nx.to_number()

Nx