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2022/README.md

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 My (attempted) solutions to [Advent of Code 2022](https://adventofcode.com/2022) in Elixir.
 
-<img width="869" alt="image" src="https://user-images.githubusercontent.com/498229/206862407-902d0162-93b1-46c6-8bf1-1e7ec7e7f819.png">
+<img width="869" alt="image" src="https://user-images.githubusercontent.com/498229/207063420-9e176055-d40c-4b33-a826-368c04a7b75d.png">
 
 ## Running:
 

2022/day11.exs

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+defmodule Monkey do
+  use GenServer
+
+  defstruct [
+    :num,
+    :items_caught,
+    :operation,
+    :divisor,
+    :true_monkey,
+    :false_monkey,
+    :inspected_count
+  ]
+
+  # Server
+  #########
+
+  def init(%Monkey{} = monkey) do
+    {:ok, {monkey, _monkeys = %{}}}
+  end
+
+  def handle_cast({:catch, item}, {monkey, monkies}) do
+    monkey = catch_item(monkey, item)
+    {:noreply, {monkey, monkies}}
+  end
+
+  def handle_call({:register, monkies}, _from, {monkey, _monkies}) do
+    {:reply, :ok, {monkey, monkies}}
+  end
+
+  def handle_call(:turn, _from, {monkey, monkies}) do
+    monkey = do_business(monkey, monkies)
+    {:reply, :done, {%Monkey{monkey | items_caught: []}, monkies}}
+  end
+
+  def handle_call(:get_count, _from, {monkey, monkies}) do
+    {:reply, monkey.inspected_count, {monkey, monkies}}
+  end
+
+  # Client
+  #########
+  def throw(monkey, item), do: GenServer.cast(monkey, {:catch, item})
+  def register(monkey, monkeys), do: GenServer.call(monkey, {:register, monkeys})
+  def take_turn(monkey), do: GenServer.call(monkey, :turn)
+  def report_count(monkey), do: GenServer.call(monkey, :get_count)
+
+  # Monkey business
+  ##################
+
+  defp catch_item(monkey, item), do: %Monkey{monkey | items_caught: [item | monkey.items_caught]}
+
+  defp do_business(monkey, monkies) do
+    count =
+      for item <- Enum.reverse(monkey.items_caught), reduce: 0 do
+        count ->
+          item = monkey.operation.(item) |> div(3)
+
+          to_monkey =
+            if rem(item, monkey.divisor) == 0 do
+              monkey.true_monkey
+            else
+              monkey.false_monkey
+            end
+
+          throw(monkies[to_monkey], item)
+          count + 1
+      end
+
+    %Monkey{monkey | items_caught: [], inspected_count: monkey.inspected_count + count}
+  end
+end
+
+defmodule Day11 do
+  def part1(input) do
+    monkies = setup_monkies(input)
+    order = monkies |> Map.keys() |> Enum.sort()
+
+    run_rounds(20, monkies, order)
+
+    order
+    |> Enum.map(&Monkey.report_count(monkies[&1]))
+    |> Enum.sort(:desc)
+    |> Enum.take(2)
+    |> Enum.reduce(&Kernel.*/2)
+  end
+
+  def setup_monkies(input) do
+    monkies =
+      input
+      |> Enum.with_index()
+      |> Map.new(fn {monkey, idx} ->
+        {:ok, pid} = GenServer.start_link(Monkey, monkey)
+        {idx, pid}
+      end)
+
+    Enum.each(monkies, fn {_k, monkey} -> Monkey.register(monkey, monkies) end)
+
+    monkies
+  end
+
+  defp run_rounds(0, _monkies, _order), do: :ok
+
+  defp run_rounds(rounds, monkies, order) do
+    Enum.each(order, &Monkey.take_turn(monkies[&1]))
+    run_rounds(rounds - 1, monkies, order)
+  end
+
+  def part2(_input) do
+    :ok
+  end
+
+  def input do
+    with [input_filename] <- System.argv(),
+         {:ok, input} <- File.read(input_filename) do
+      input
+      |> String.split("\n\n")
+      |> Enum.map(fn monkey ->
+        [
+          <<"Monkey ", monkey_num::binary-1, ":">>,
+          "Starting items: " <> starting_items,
+          <<"Operation: new = old ", op::binary-1, " ", operand::binary>>,
+          "Test: divisible by " <> divisor,
+          "If true: throw to monkey " <> true_monkey,
+          "If false: throw to monkey " <> false_monkey
+        ] = monkey |> String.trim() |> String.split("\n") |> Enum.map(&String.trim/1)
+
+        starting_items = String.split(starting_items, ", ")
+
+        [monkey_num, divisor, true_monkey, false_monkey | starting_items] =
+          Enum.map(
+            [monkey_num, divisor, true_monkey, false_monkey] ++ starting_items,
+            &String.to_integer/1
+          )
+
+        operation =
+          case {op, operand} do
+            {"+", "old"} -> fn old -> old + old end
+            {"*", "old"} -> fn old -> old * old end
+            {"+", operand} -> fn old -> old + String.to_integer(operand) end
+            {"*", operand} -> fn old -> old * String.to_integer(operand) end
+          end
+
+        %Monkey{
+          num: monkey_num,
+          items_caught: Enum.reverse(starting_items),
+          operation: operation,
+          divisor: divisor,
+          true_monkey: true_monkey,
+          false_monkey: false_monkey,
+          inspected_count: 0
+        }
+      end)
+    else
+      _ -> :error
+    end
+  end
+
+  #######################
+  # HERE BE BOILERPLATE #
+  #######################
+
+  def run do
+    case input() do
+      :error -> print_usage()
+      input -> run_parts_with_timer(input)
+    end
+  end
+
+  defp run_parts_with_timer(input) do
+    run_with_timer(1, fn -> part1(input) end)
+    run_with_timer(2, fn -> part2(input) end)
+  end
+
+  defp run_with_timer(part, fun) do
+    {time, result} = :timer.tc(fun)
+    IO.puts("Part #{part} (completed in #{format_time(time)}):\n")
+    IO.puts("#{result}\n")
+  end
+
+  defp format_time(μsec) when μsec < 1_000, do: "#{μsec}μs"
+  defp format_time(μsec) when μsec < 1_000_000, do: "#{μsec / 1000}ms"
+  defp format_time(μsec), do: "#{μsec / 1_000_000}s"
+
+  defp print_usage do
+    IO.puts("Usage: elixir day11.exs input_filename")
+  end
+end
+
+# Day11.run()