advent13.exs

defmodule Advent13 do
  def part1(rows),
    do:
      parse(rows)
      |> Enum.filter(fn [level, range] -> is_caught?(level, range, 0) end)
      |> Enum.map(fn [level, range] -> level * range end)
      |> Enum.sum()
      |> IO.inspect()

  def part2(rows), do: recurse(0, parse(rows)) |> IO.inspect()

  def recurse(delay, rows) do
    case Enum.any?(rows, fn [level, range] -> is_caught?(level, range, delay) end) do
      true -> recurse(delay + 1, rows)
      false -> delay
    end
  end

  def is_caught?(level, range, delay), do: rem(delay + level, 2 * (range - 1)) == 0

  def parse(rows),
    do:
      rows
      |> Enum.map(fn [a, b] -> [String.to_integer(a), String.to_integer(b)] end)
      |> Enum.sort(fn [_, r1], [_, r2] -> r1 < r2 end)
end

File.read!("input13")
|> String.trim()
|> String.split("\n")
|> Enum.map(fn row -> String.split(row, ": ") end)
|> Advent13.part1()

File.read!("input13")
|> String.trim()
|> String.split("\n")
|> Enum.map(fn row -> String.split(row, ": ") end)
|> Advent13.part2()