aoc2020day2.ex

defmodule Day2 do
  def read_input do
    File.read!("input/day2.txt")
    |> String.split("\n", trim: true)
    |> Enum.map(&(Regex.scan(~r/(\d+)-(\d+) (\w+): (.*)/, &1)))
    |> Enum.map(fn [[_, min, max, char, text]] -> {
      String.to_integer(min),
      String.to_integer(max),
      char,
      text
    } end)
  end

  def check_part_1 {min, max, char, text} do
    count = String.graphemes(text)
            |> Enum.count(&(&1 == char))

    count >= min and
    count <= max
  end

  def check_part_2 {min, max, char, text} do
    c1 = String.at(text, min - 1) == char
    c2 = String.at(text, max - 1) == char

    (c1 or c2) and !(c1 && c2)
  end

  def part1 do
    check(&check_part_1/1)
  end

  def part2 do
    check(&check_part_2/1)
  end

  def check(part) do
    read_input()
    |> Enum.map(part)
    |> Enum.count(&(&1 == true))
    |> IO.inspect
  end
end