Day 5

Part 1

input =
  IO.getn("input: ", 1_000_000)
  |> String.split("\n", trim: true)

defmodule AdventOfCode.DayFive do
  def solve_part_one(input) do
    input
    |> parse()
    |> Enum.filter(fn [first, second] ->
      elem(first, 0) == elem(second, 0) ||
        elem(first, 1) == elem(second, 1)
    end)
    |> solve()
  end

  def solve_part_two(input) do
    input
    |> parse()
    |> solve()
  end

  defp parse(input) do
    input
    |> Enum.map(fn pair ->
      [first, second] = String.split(pair, " -> ")

      [x1, y1] =
        String.split(first, ",")
        |> Enum.map(fn el ->
          {number, _rest} = Integer.parse(el)
          number
        end)

      [x2, y2] =
        String.split(second, ",")
        |> Enum.map(fn el ->
          {number, _rest} = Integer.parse(el)
          number
        end)

      [{x1, y1}, {x2, y2}]
    end)
  end

  defp solve(input) do
    input
    |> Enum.map(fn [{x1, y1}, {x2, y2}] ->
      cond do
        x1 == x2 ->
          y1..y2 |> Enum.map(fn el -> {x1, el} end)

        y1 == y2 ->
          x1..x2 |> Enum.map(fn el -> {el, y1} end)

        true ->
          Enum.zip(x1..x2, y1..y2)
      end
    end)
    |> List.flatten()
    |> Enum.frequencies()
    |> Enum.filter(fn {_pair, freq} -> freq >= 2 end)
    |> Enum.count()
  end
end

AdventOfCode.DayFive.solve_part_one(input)

Part 2

AdventOfCode.DayFive.solve_part_two(input)