adventofcode-day1

day1.exs

defmodule Day1 do
  def read_input do
    "input.txt"
    |> File.stream!()
    |> Stream.map(&String.trim/1)
    |> Stream.map(&String.to_integer/1)
  end

  def combine_freq(input) do
    Enum.reduce(input, &Kernel.+/2)
  end

  def find_repeat_freq(state \\ {MapSet.new(), 0}, input) do
    state =
      input
      |> Enum.reduce_while(state, fn x, {seen_freq, sum} ->
        freq = x + sum

        if MapSet.member?(seen_freq, freq) do
          {:halt, {:found, freq}}
        else
          {:cont, {MapSet.put(seen_freq, freq), freq}}
        end
      end)

    case state do
      {:found, freq} -> freq
      state -> find_repeat_freq(state, input)
    end
  end
end

combined = Day1.combine_freq(Day1.read_input())
repeated = Day1.find_repeat_freq(Day1.read_input())

IO.puts("Combined freq is: #{combined}")
IO.puts("Repeated freq is: #{repeated}")