Day 5: Hydrothermal Venture

Intro

https://adventofcode.com/2021/day/5

Input

defmodule MM do
  def get_min_and_max_values(lines) do
    x_min =
      lines
      |> Enum.map(fn {{x1, _y1}, {x2, _y2}} -> min(x1, x2) end)
      |> Enum.min()

    x_max =
      lines
      |> Enum.map(fn {{x1, _y1}, {x2, _y2}} -> max(x1, x2) end)
      |> Enum.max()

    y_min =
      lines
      |> Enum.map(fn {{_x1, y1}, {_x2, y2}} -> min(y1, y2) end)
      |> Enum.min()

    y_max =
      lines
      |> Enum.map(fn {{_x1, y1}, {_x2, y2}} -> max(y1, y2) end)
      |> Enum.max()

    [x_min, x_max, y_min, y_max]
  end
end

{:module, MM, <<70, 79, 82, 49, 0, 0, 9, ...>>, {:get_min_and_max_values, 1}}

input_test =
  """
  0,9 -> 5,9
  8,0 -> 0,8
  9,4 -> 3,4
  2,2 -> 2,1
  7,0 -> 7,4
  6,4 -> 2,0
  0,9 -> 2,9
  3,4 -> 1,4
  0,0 -> 8,8
  5,5 -> 8,2
  """
  |> String.split("\n", trim: true)
  |> Enum.map(fn l ->
    [x1, y1, x2, y2] = String.split(l, [" -> ", ","])

    {{String.to_integer(x1), String.to_integer(y1)},
     {String.to_integer(x2), String.to_integer(y2)}}
  end)

[x_min_test, x_max_test, y_min_test, y_max_test] = MM.get_min_and_max_values(input_test)

[0, 9, 0, 9]

input =
  File.read!("input05.txt")
  |> String.split("\n", trim: true)
  |> Enum.map(fn l ->
    [x1, y1, x2, y2] = String.split(l, [" -> ", ","])

    {{String.to_integer(x1), String.to_integer(y1)},
     {String.to_integer(x2), String.to_integer(y2)}}
  end)

[x_min, x_max, y_min, y_max] = MM.get_min_and_max_values(input)

[11, 989, 10, 989]

Part 1

defmodule Matrix do
  def expand_line({{x1, y}, {x2, y}}) do
    for x <- x1..x2 do
      {x, y}
    end
  end

  def expand_line({{x, y1}, {x, y2}}) do
    for y <- y1..y2 do
      {x, y}
    end
  end

  def expand_line({{x1, y1}, {x2, y2}}) do
    x_min = min(x1, x2)
    x_max = max(x1, x2)

    y_step = if y1 > y2, do: -1, else: 1
    x_step = if x1 > x2, do: -1, else: 1

    steps = x_max - x_min

    for s <- 0..steps do
      {x1 + s * x_step, y1 + s * y_step}
    end
  end
end

i =
  input_test
  |> Enum.filter(fn {{x1, y1}, {x2, y2}} -> x1 == x2 or y1 == y2 end)
  |> Enum.map(fn line -> Matrix.expand_line(line) end)
  |> List.flatten()
  |> Enum.group_by(fn {x, y} -> {x, y} end, fn _ -> 1 end)
  |> Enum.map(fn {k, v} -> {k, Enum.sum(v)} end)
  |> Enum.filter(fn {_k, v} -> v > 1 end)
  |> Enum.count()

5

i =
  input
  |> Enum.filter(fn {{x1, y1}, {x2, y2}} -> x1 == x2 or y1 == y2 end)
  |> Enum.map(fn line -> Matrix.expand_line(line) end)
  |> List.flatten()
  |> Enum.group_by(fn {x, y} -> {x, y} end, fn _ -> 1 end)
  |> Enum.map(fn {k, v} -> {k, Enum.sum(v)} end)
  |> Enum.filter(fn {_k, v} -> v > 1 end)
  |> Enum.count()

6267

Correct: 6267

Part 2

i =
  input_test
  |> Enum.map(fn line -> Matrix.expand_line(line) end)
  |> List.flatten()
  |> Enum.group_by(fn {x, y} -> {x, y} end, fn _ -> 1 end)
  |> Enum.map(fn {k, v} -> {k, Enum.sum(v)} end)
  |> Enum.filter(fn {_k, v} -> v > 1 end)
  |> Enum.count()

12

i =
  input
  |> Enum.map(fn line -> Matrix.expand_line(line) end)
  |> List.flatten()
  |> Enum.group_by(fn {x, y} -> {x, y} end, fn _ -> 1 end)
  |> Enum.map(fn {k, v} -> {k, Enum.sum(v)} end)
  |> Enum.filter(fn {_k, v} -> v > 1 end)
  |> Enum.count()

20196

Correct: 20196