Advent of code 2021 - day 5 - part 2 - solution

advent-of-code-2021-day5.ex

defmodule Vents do
  def parsepoint(point) do
    point
    |> String.split(",", trim: true)
    |> Enum.map(&String.trim/1)
    |> Enum.map(&String.to_integer/1)
  end

  def parseline(line) do
    line
    |> String.split("->", trim: true)
    |> Enum.map(&parsepoint/1)
  end

  def read(path) do
    File.read!(path)
    |> String.split("\n")
    |> Enum.map(&parseline/1)
  end

  def points([x1, y1], [x2, y2]) when x1 != x2 and y1 != y2 do
    xs = Enum.to_list(x1..x2)
    ys = Enum.to_list(y1..y2)
    Enum.zip(xs, ys)
  end

  def points([x1, y1], [x2, y2]) when x1 == x2 do
    Enum.to_list(y1..y2)
    |> Enum.map(fn y -> {x1, y} end)
  end

  def points([x1, y1], [x2, y2]) when y1 == y2 do
    Enum.to_list(x1..x2)
    |> Enum.map(fn x -> {x, y1} end)
  end

  def run() do
    all =
      read("./input/day5.txt")
      |> Enum.map(fn [a, b] -> points(a, b) end)
      |> List.flatten()
      |> Enum.frequencies()
      |> Enum.filter(fn {k, v} -> v >= 2 end)
      |> Enum.count()
  end
end