From 791d6d9c699ed0947bed9c9390e5953cd5c59834 Mon Sep 17 00:00:00 2001
From: Dustin Swan <dustin@dustinswan.com>
Date: Sun, 29 Dec 2024 17:50:28 -0700
Subject: [PATCH] Day 24. Got part 1 pretty easily, but now I\'m not sure I
 should be using maps for the gates. Checking in now so I can refactor into
 just lists

---
 day24/main.exs | 91 ++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 91 insertions(+)
 create mode 100644 day24/main.exs

diff --git a/day24/main.exs b/day24/main.exs
new file mode 100644
index 0000000..7aa3bbc
--- /dev/null
+++ b/day24/main.exs
@@ -0,0 +1,91 @@
+defmodule Day24 do
+  def run do
+    {wires, gates} = parse_input("test.txt")
+
+    # part1
+    part1 = run_loop(wires, gates) |> wire_value("z") |> b_to_d()
+    dbg(part1)
+
+    # part2
+    x = wire_value(wires, "x") |> b_to_d()
+    y = wire_value(wires, "y") |> b_to_d()
+    target = (x + y) |> d_to_b()
+    dbg(target)
+    dbg(b_to_d(target))
+  end
+
+  defp b_to_d(bin) do
+    :erlang.binary_to_integer(Integer.to_string(bin), 2)
+  end
+
+  defp d_to_b(dec) do
+    Integer.to_string(dec, 2) |> String.to_integer()
+  end
+
+  defp wire_value(wires, char) do
+    wires
+    |> Enum.filter(fn {k, _} -> String.starts_with?(k, char) end)
+    |> Enum.sort()
+    |> Enum.reduce([], fn {_, v}, acc -> [v | acc] end)
+    |> Integer.undigits()
+  end
+
+  defp run_loop(wires, gates) do
+    new_wires = run(wires, gates)
+
+    if map_size(new_wires) == map_size(wires) do
+      wires
+    else
+      run_loop(new_wires, gates)
+    end
+  end
+
+  defp run(wires, gates) do
+    Enum.reduce(gates, wires, fn {{left, right}, effects}, acc ->
+      l = Map.get(wires, left, nil)
+      r = Map.get(wires, right, nil)
+
+      if !is_nil(l) and !is_nil(r) do
+        Enum.reduce(effects, acc, fn {op, output}, acc2 ->
+          res = op.(l, r)
+          Map.put(acc2, output, res)
+        end)
+      else
+        acc
+      end
+    end)
+  end
+
+  defp parse_input(file) do
+    [wires, gates] =
+      File.read!(file)
+      |> String.trim()
+      |> String.split("\n\n")
+      |> Enum.map(&String.split(&1, "\n"))
+
+    wires =
+      Enum.reduce(wires, %{}, fn el, map ->
+        [wire, value] = String.split(el, ": ")
+        Map.put(map, wire, String.to_integer(value))
+      end)
+
+    gates =
+      Enum.reduce(gates, %{}, fn el, map ->
+        [logic, output] = String.split(el, " -> ")
+        [left, op, right] = String.split(logic, " ")
+
+        op =
+          case op do
+            "AND" -> &Bitwise.band/2
+            "OR" -> &Bitwise.bor/2
+            "XOR" -> &Bitwise.bxor/2
+          end
+
+        Map.update(map, {left, right}, [{op, output}], fn acc -> [{op, output} | acc] end)
+      end)
+
+    {wires, gates}
+  end
+end
+
+Day24.run()