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+# AOC 2022 - Day 3
+
+```elixir
+Mix.install([
+  {:req, "~> 0.3.3"}
+])
+```
+
+## Puzzle description
+
+[Day 3: Rucksack Reorganization](https://adventofcode.com/2022/day/3).
+
+## Input
+
+```elixir
+defmodule Load do
+  def input do
+    aoc_session = System.fetch_env!("LB_AOC_SESSION")
+    input_url = "https://adventofcode.com/2022/day/3/input"
+    Req.get!(input_url, headers: [cookie: "session=#{aoc_session}"]).body
+  end
+end
+```
+
+```elixir
+defmodule A do
+  def intersection(str1, str2) do
+    str1_set = MapSet.new(String.graphemes(str1))
+    str2_set = MapSet.new(String.graphemes(str2))
+    MapSet.intersection(str1_set, str2_set)
+  end
+end
+
+A.intersection("hello", "world")
+```
+
+## Solution
+
+```elixir
+defmodule Util do
+  @items String.split("abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ", "", trim: true)
+
+  def value_of(item) do
+    Enum.find_index(@items, fn c -> c == item end) + 1
+  end
+
+  def process(input) do
+    input
+    |> String.trim()
+    |> String.split("\n", trim: true)
+  end
+
+  def intersection(str1, str2) do
+    str1_set = MapSet.new(String.graphemes(str1))
+    str2_set = MapSet.new(String.graphemes(str2))
+    MapSet.intersection(str1_set, str2_set)
+  end
+
+  def intersection(str1, str2, str3) do
+    str1_set = MapSet.new(String.graphemes(str1))
+    str2_set = MapSet.new(String.graphemes(str2))
+    str3_set = MapSet.new(String.graphemes(str3))
+    intersection = MapSet.intersection(str1_set, str2_set)
+    MapSet.intersection(intersection, str3_set)
+  end
+end
+```
+
+```elixir
+defmodule Part1 do
+  def run(input) do
+    input
+    |> Util.process()
+    |> Enum.map(&String.split_at(&1, div(String.length(&1), 2)))
+    |> Enum.reduce(0, fn {first, second}, acc ->
+      priority =
+        Util.intersection(first, second)
+        |> MapSet.to_list()
+        |> List.first()
+        |> Util.value_of()
+
+      acc + priority
+    end)
+  end
+end
+
+defmodule Part2 do
+  def run(input) do
+    input
+    |> Util.process()
+    |> Enum.chunk_every(3)
+    |> Enum.map(fn [items1, items2, items3] ->
+      Util.intersection(items1, items2, items3)
+      |> MapSet.to_list()
+      |> List.first()
+      |> Util.value_of()
+    end)
+    |> Enum.reduce(&+/2)
+  end
+end
+
+ExUnit.start(autorun: false)
+
+defmodule Test do
+  use ExUnit.Case, async: true
+  @example_input ~s(vJrwpWtwJgWrhcsFMMfFFhFp
+jqHRNqRjqzjGDLGLrsFMfFZSrLrFZsSL
+PmmdzqPrVvPwwTWBwg
+wMqvLMZHhHMvwLHjbvcjnnSBnvTQFn
+ttgJtRGJQctTZtZT
+CrZsJsPPZsGzwwsLwLmpwMDw)
+  @input Load.input()
+
+  test "it loads the input" do
+    assert String.length(@input) > 0
+  end
+
+  test "part 1 example" do
+    assert Part1.run(@example_input) === 157
+  end
+
+  test "part 1" do
+    assert Part1.run(@input) === 8105
+  end
+
+  test "part 2 example" do
+    assert Part2.run(@example_input) === 70
+  end
+
+  test "part 2" do
+    assert Part2.run(@input) === 0
+  end
+end
+
+ExUnit.run()
+```