Day 5: Hydrothermal Venture

Setup

Mix.install([
  {:kino, "~> 0.4.1"}
])

:ok

Input

input = Kino.Input.textarea(label = "Input")

Part 1

defmodule M do
  def parse(input) do
    input
    |> String.split("\n", trim: true)
    |> Enum.map(fn row ->
      ~r/(?\d+),(?\d+) -> (?\d+),(?\d+)/
      |> Regex.named_captures(row)
      |> Enum.map(fn {k, v} -> {k, String.to_integer(v)} end)
      |> Map.new()
    end)
  end

  def lines_to_points(lines) do
    lines
    |> Enum.map(&line_to_points(&1))
    |> Enum.flat_map(& &1)
  end

  def line_to_points(line) do
    cond do
      line["x1"] == line["x2"] ->
        line["y1"]..line["y2"] |> Enum.map(&{line["x1"], &1})

      line["y1"] == line["y2"] ->
        line["x1"]..line["x2"] |> Enum.map(&{&1, line["y1"]})

      true ->
        []
    end
  end
end

Kino.Input.read(input)
|> M.parse()
|> M.lines_to_points()
|> Enum.frequencies()
|> Enum.count(fn {_k, v} -> v > 1 end)

7473

Part 2

defmodule M do
  def parse(input) do
    input
    |> String.split("\n", trim: true)
    |> Enum.map(fn row ->
      ~r/(?\d+),(?\d+) -> (?\d+),(?\d+)/
      |> Regex.named_captures(row)
      |> Enum.map(fn {k, v} -> {k, String.to_integer(v)} end)
      |> Map.new()
    end)
  end

  def lines_to_points(lines) do
    lines
    |> Enum.map(&line_to_points(&1))
    |> Enum.flat_map(& &1)
  end

  def line_to_points(line) do
    cond do
      line["x1"] == line["x2"] ->
        line["y1"]..line["y2"] |> Enum.map(&{line["x1"], &1})

      line["y1"] == line["y2"] ->
        line["x1"]..line["x2"] |> Enum.map(&{&1, line["y1"]})

      abs(line["x1"] - line["x2"]) == abs(line["y1"] - line["y2"]) ->
        Enum.zip(line["x1"]..line["x2"], line["y1"]..line["y2"])

      true ->
        []
    end
  end
end

Kino.Input.read(input)
|> M.parse()
|> M.lines_to_points()
|> Enum.frequencies()
|> Enum.count(fn {_k, v} -> v > 1 end)

24164