Day6

Mix.install([
  {:kino, "~> 0.11.3"}
])

Section

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

defmodule Sol6 do
  def strlist2numlist(s) do
    Enum.map(s, fn n -> String.to_integer(n) end)
  end

  def read_input_part1(text) do
    [time, distance] = String.split(text, "\n")
    times = Sol6.strlist2numlist(tl(String.split(time)))
    distances = Sol6.strlist2numlist(tl(String.split(distance)))
    Enum.zip(times, distances)
  end

  def read_input_part2(text) do
    [time, distance] = String.split(text, "\n")

    {Regex.replace(~r/[^\d]/, time, "") |> String.to_integer(),
     Regex.replace(~r/[^\d]/, distance, "") |> String.to_integer()}
  end

  def solve({time, distance}) do
    {r1, r2} = quadratic(1, -time, distance)
    {m1, m2} = {ceil(r1 + 1.0e-6), floor(r2 - 1.0e-6)}
    m2 - m1 + 1
  end

  def quadratic(a, b, c) do
    {(-b - :math.sqrt(b * b - 4 * a * c)) / (2 * a),
     (-b + :math.sqrt(b * b - 4 * a * c)) / (2 * a)}
  end
end

# Part 1
input_data = Sol6.read_input_part1(Kino.Input.read(input))

Enum.map(input_data, fn d -> Sol6.solve(d) end)
|> Enum.reduce(1, fn x, acc -> x * acc end)

# Part 2
input_data = Sol6.read_input_part2(Kino.Input.read(input))
Sol6.solve(input_data)