From d73fb26f45ab871515020bd470cf03fdc91a705e Mon Sep 17 00:00:00 2001
From: Justin Wernick <j.wernick@eyeo.com>
Date: Mon, 16 Sep 2024 16:39:57 +0200
Subject: Day 7

---
 2015/day7.exs | 81 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 81 insertions(+)
 create mode 100644 2015/day7.exs

(limited to '2015/day7.exs')

diff --git a/2015/day7.exs b/2015/day7.exs
new file mode 100644
index 0000000..c38a931
--- /dev/null
+++ b/2015/day7.exs
@@ -0,0 +1,81 @@
+gates = File.stream!("inputs/day7.txt")
+
+gateRegex = ~r/(([a-z]+|[0-9]+) )?(([A-Z]+) )?([a-z]+|[0-9]+) -> ([a-z]+)/
+
+circuit =
+  Enum.reduce(gates, Map.new(), fn gate, acc ->
+    [_, _, input1, _, op, input2, output] = Regex.run(gateRegex, gate)
+
+    inputs =
+      Enum.filter([input1, input2], fn input -> input != "" end)
+      |> Enum.map(fn input ->
+        case Integer.parse(input) do
+          {num, ""} -> num
+          :error -> input
+        end
+      end)
+
+    Map.put(acc, output, {op, inputs})
+  end)
+
+defmodule MemoizedCircuitSolver do
+  use Agent
+
+  def start do
+    Agent.start_link(fn -> %{} end, name: __MODULE__)
+  end
+
+  def evaluate(circuit, id) when is_integer(id) do
+    id
+  end
+
+  def evaluate(circuit, id) do
+    cached_value = Agent.get(__MODULE__, &Map.get(&1, {circuit, id}))
+
+    if cached_value do
+      cached_value
+    else
+      {op, inputs} = Map.get(circuit, id)
+      inputs = Enum.map(inputs, fn i -> evaluate(circuit, i) end)
+
+      result =
+        case op do
+          "" ->
+            [result] = inputs
+            result
+
+          "NOT" ->
+            [input] = inputs
+            Bitwise.bnot(input)
+
+          "AND" ->
+            Enum.reduce(inputs, &Bitwise.band(&1, &2))
+
+          "OR" ->
+            Enum.reduce(inputs, &Bitwise.bor(&1, &2))
+
+          "LSHIFT" ->
+            [input, amount] = inputs
+            Bitwise.bsl(input, amount)
+
+          "RSHIFT" ->
+            [input, amount] = inputs
+            Bitwise.bsr(input, amount)
+        end
+
+      Agent.update(__MODULE__, &Map.put(&1, {circuit, id}, result))
+      result
+    end
+  end
+end
+
+{:ok, _} = MemoizedCircuitSolver.start()
+
+aValue = MemoizedCircuitSolver.evaluate(circuit, "a")
+
+IO.puts("Initial A value: #{aValue}")
+
+secondCircuit = Map.put(circuit, "b", {"", [aValue]})
+
+aValue2 = MemoizedCircuitSolver.evaluate(secondCircuit, "a")
+IO.puts("Final A value: #{aValue2}")
-- 
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