2024 Day 13 (just parsing input + notes, no solution)

2024/day13_wip.exs

@@ -0,0 +1,81 @@
+#!/usr/bin/env elixir
+defmodule Day13 do
+  defmodule Machine do
+    defstruct [:a, :b, :prize]
+  end
+
+  def part1(input) do
+    input
+    # these are equivalent linear equations
+    # know how to do it algebraically, but not algorithmically
+    # e.g. for first example
+    # 
+    # 94a + 22b - 8400 = 34a + 67b - 5400
+    # 94a + 22b - 3000 = 34a + 67b
+    # 60a + 22b - 3000 = 67b
+    # 60a - 3000 = 45b
+    # 4a - 200 = 3b
+    # a = 3/4b + 50
+    # 34(3/4b + 50) + 67b - 5400 = 0
+    # 25.5b + 1700 + 67b - 5400 = 0
+    # 92.5b = 3700
+    # b = 40
+    # 34a + 67(40) = 5400
+    # 34a + 2680 = 5400
+    # 34a = 2720
+    # a = 80
+  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 machine ->
+        machine
+        |> String.split(["+", ",", "=", "\n"], trim: true)
+        |> tl()
+        |> Enum.take_every(2)
+        |> Enum.map(&String.to_integer/1)
+      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("#{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 day13.exs input_filename")
+  end
+end
+
+# Day13.run()