Day 9
Two brute forces in a row! Also, the first part was reminiscent of Day 1 
defmodule AdventOfCode.Y2020.Day9 do
@moduledoc """
Problem Link: https://adventofcode.com/2020/day/9
"""
use AdventOfCode.Helpers.InputReader, year: 2020, day: 9
def run_1, do: input!() |> process() |> find_invalid()
def run_2, do: input!() |> process() |> contiguous_list()
def process(input), do: Enum.map(String.split(input, "\n"), &String.to_integer/1)
defp find_invalid(data) do
{frame, [v | _] = next} = Enum.split(data, 25)
(invalid?(v, MapSet.new(frame)) && v) || find_invalid(tl(frame) ++ next)
end
def invalid?(value, frame), do: Enum.empty?(Enum.filter(frame, &((value - &1) in frame)))
defp contiguous_list(data), do: contiguous_list(find_invalid(data), data)
defp contiguous_list(value, [h | rest]) do
case contiguous_list(List.wrap(h), rest, value) do
:bigger -> contiguous_list(value, rest)
lst -> Enum.max(lst) + Enum.min(lst)
end
end
def contiguous_list(data, [h | rest], value) do
lst = [h | data]
case Enum.sum(lst) do
^value -> lst
n when n > value -> :bigger
_ -> contiguous_list(lst, rest, value)
end
end
end