Add 2024 Day 21 WIP - probably give up

2024/day21_wip.exs

@@ -0,0 +1,133 @@
+#!/usr/bin/env elixir
+defmodule Day21 do
+  @numpad %{
+    "7" => {0, 0},
+    "8" => {1, 0},
+    "9" => {2, 0},
+    "4" => {0, 1},
+    "5" => {1, 1},
+    "6" => {2, 1},
+    "1" => {0, 2},
+    "2" => {1, 2},
+    "3" => {2, 2},
+    "0" => {1, 3},
+    "A" => {2, 3}
+  }
+
+  @keypad %{
+    "^" => {1, 0},
+    "A" => {2, 0},
+    "<" => {0, 1},
+    "v" => {1, 1},
+    ">" => {2, 1}
+  }
+
+  def part1(input) do
+    Enum.map(input, &complexity/1)
+  end
+
+  def complexity(code) do
+    length =
+      code
+      |> derive_keys(@numpad)
+      # asdfsadfsdafdfs for the robot, some derived combinations are shorter, why?
+      # Maybe going left non-sequentially is expensive because of round trips to the A buttom
+      # so sequentially is cheaper?
+      # Need to figure out what the situation that causes a longer sequence is
+      |> derive_keys(@keypad)
+      |> derive_keys(@keypad)
+      |> byte_size()
+      |> dbg()
+
+    {numeric, "A"} = Integer.parse(code)
+    dbg(numeric)
+
+    numeric * length
+  end
+
+  def derive_keys(seq, pad) do
+    String.graphemes("A" <> seq)
+    |> Enum.chunk_every(2, 1, :discard)
+    |> Enum.map_join("", fn [a, b] -> keys(a, b, pad) <> "A" end)
+  end
+
+  def numpad, do: @numpad
+
+  def keys(a, b, pad) do
+    {x1, y1} = Map.fetch!(pad, a)
+    {x2, y2} = Map.fetch!(pad, b)
+    dx = x2 - x1
+    dy = y2 - y1
+
+    keys_x = keys_x(dx)
+    keys_y = keys_y(dy)
+
+    # avoid the gap
+    if dx < 0 do
+      keys_y <> keys_x
+    else
+      keys_x <> keys_y
+    end
+  end
+
+  def keys_x(-2), do: "<<"
+  def keys_x(-1), do: "<"
+  def keys_x(0), do: ""
+  def keys_x(1), do: ">"
+  def keys_x(2), do: ">>"
+
+  def keys_y(-3), do: "^^^"
+  def keys_y(-2), do: "^^"
+  def keys_y(-1), do: "^"
+  def keys_y(0), do: ""
+  def keys_y(1), do: "v"
+  def keys_y(2), do: "vv"
+  def keys_y(3), do: "vvv"
+
+  def keypad, do: @keypad
+
+  def part2(_input) do
+    :ok
+  end
+
+  def input do
+    with [input_filename] <- System.argv(),
+         {:ok, input} <- File.read(input_filename) do
+      String.split(input, "\n", trim: true)
+    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("#{inspect(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 day21.exs input_filename")
+  end
+end
+
+# Day21.run()