Advent of Code 2022 - Day 3

Day 3: Rucksack Reorganization

Description

Utils

defmodule Load do
  def file(path) do
    File.read!(__DIR__ <> path)
    |> String.split("\n", trim: true)
  end

  def string(value) do
    value |> String.split("\n", trim: true)
  end
end

Input

input = Load.file("/data/day03.txt")

Part 1

Find the item type that appears in both compartments of each rucksack. What is the sum of the priorities of those item types?

defmodule Part1 do
  def get_same(splitted_line) do
    compartment1 = elem(splitted_line, 0) |> String.graphemes()
    compartment2 = elem(splitted_line, 1) |> String.graphemes()

    compartment1
    |> Enum.find(fn item ->
      is_in_compartment(item, compartment2)
    end)
  end

  def split_line(line) do
    length = line |> String.length() |> Integer.floor_div(2)
    line |> String.split_at(length)
  end

  def to_value(item) do
    <> = item

    if v > 64 and v < 91 do
      v - 65 + 27
    else
      v - 96
    end
  end

  defp is_in_compartment(item, compartment) do
    compartment |> Enum.find(&amp;(&amp;1 === item))
  end
end

input
|> Enum.map(&amp;Part1.split_line/1)
|> Enum.map(&amp;Part1.get_same/1)
|> Enum.map(&amp;Part1.to_value/1)
|> Enum.sum()

Result

8176

Part 2

Find the item type that corresponds to the badges of each three-Elf group. What is the sum of the priorities of those item types?

defmodule Part2 do
  def find_common(group) do
    [bag1 | rest_of_bags] = group

    bag1
    |> String.graphemes()
    |> Enum.find(fn item ->
      find_common(item, rest_of_bags)
    end)
  end

  defp find_common(item, [bag | rest_of_bags]) do
    case bag |> String.graphemes() |> Enum.find(&(&1 === item)) do
      nil -> false
      item -> find_common(item, rest_of_bags)
    end
  end

  defp find_common(item, []) do
    item
  end
end

input
|> Enum.chunk_every(3)
|> Enum.map(&Part2.find_common/1)
|> Enum.map(&Part1.to_value/1)
|> Enum.sum()

Result

2689