From 356164ec46eaa53958af4514f3f466f37c1407b6 Mon Sep 17 00:00:00 2001
From: Philip Corliss <pcorliss@50projects.com>
Date: Wed, 20 Dec 2023 16:46:50 -0600
Subject: [PATCH] 2023 Day 20 Part 2 Generalized Solution

---
 2023/20/pulses.rb           | 58 +++++++++++++++++++++++++++++++++++--
 2023/20/run.rb              |  5 +++-
 2023/20/spec/pulses_spec.rb | 15 +++++-----
 3 files changed, 66 insertions(+), 12 deletions(-)

diff --git a/2023/20/pulses.rb b/2023/20/pulses.rb
index c225cd0..eb4aa43 100644
--- a/2023/20/pulses.rb
+++ b/2023/20/pulses.rb
@@ -25,6 +25,7 @@ def initialize(input)
         @instructions[name] = [type.to_sym, *inputs]
       end
 
+
       @instructions.each do |name, (t, *outs)|
         outs.each do |out|
           if @instructions[out] && @instructions[out].first == :&
@@ -32,11 +33,19 @@ def initialize(input)
           end
         end
       end
+
+      @reverse_map = {}
+      @instructions.each do |name, (t, *outs)|
+        outs.each do |out|
+          @reverse_map[out] ||= []
+          @reverse_map[out] << name
+        end
+      end
     end
 
     LOW_HIGH = ['-low', '-high']
 
-    def send_pulse(name, from, value = 0)
+    def send_pulse(name, from, value = 0, idx = -1, block = nil)
       puts "#{from} #{LOW_HIGH[value]}-> #{name}" if @debug
       pulse_count = [0, 0]
       queue = [[name, from, value]]
@@ -45,6 +54,10 @@ def send_pulse(name, from, value = 0)
         n, f, v = queue.shift
         t, *outs = @instructions[n]
         pulse_count[v] += 1
+
+        if block
+          block.call(n, f, v, idx)
+        end
         # puts "Handling #{t} #{n} from #{f}, received #{v}" if @debug
         # binding.pry if @debug
         case t
@@ -81,6 +94,7 @@ def send_pulse(name, from, value = 0)
           if n == 'output'
             @out ||= []
             @out << v
+          elsif n == 'rx'
           else
             # raise "Unknown type #{t}"
             puts "WARN: Unknown type #{t} for #{n}" if @debug
@@ -91,8 +105,8 @@ def send_pulse(name, from, value = 0)
       pulse_count
     end
 
-    def button!
-      send_pulse('broadcaster', 'button', 0)
+    def button!(idx = -1, &block)
+      send_pulse('broadcaster', 'button', 0, idx, block)
     end
 
     def pulse_mult(cycles)
@@ -105,6 +119,44 @@ def pulse_mult(cycles)
       sum[0] * sum[1]
     end
 
+    def state_diagram
+      sd = ''
+      sd << "stateDiagram-v2" << "\n"
+      @instructions.each do |name, (t, *outs)|
+        outs.each do |out|
+          sd << "#{name} --> #{out}" << "\n"
+        end
+      end
+
+      # Output is usable with https://mermaid.live/
+      # Reveals a diagram where 4 paths with about 12-bits of state
+      # Certain bits need to be on in order to send the right pulse to the aggregator
+      sd
+    end
+
+    def rx_cycles
+      # detect modules that are connected to the rx module
+      # Assumes a modules -> aggregator_module -> rx relationship
+      aggregator_module = @reverse_map['rx'].first
+      feeder_modules = @reverse_map[aggregator_module]
+      feeder_cycle_map = feeder_modules.map {|k| [k,0]}.to_h
+      i = 0
+      until feeder_cycle_map.values.all? { |v| v > 0 } do
+        i += 1
+        raise "Too many cycles #{i}" if i > 2**12
+
+        # Normally I'd just check the state after pressing the button
+        # But the pulse we're looking for gets set and reset in the same cycle
+        button!(i) do |name, from, value, idx|
+          if value == 1 && name == aggregator_module && feeder_cycle_map[from] == 0
+            feeder_cycle_map[from] = idx
+          end
+        end
+      end
+
+      feeder_cycle_map.values.inject(:lcm)
+    end
+
     def debug!
       @debug = true
     end
diff --git a/2023/20/run.rb b/2023/20/run.rb
index 7955c0b..362c01d 100755
--- a/2023/20/run.rb
+++ b/2023/20/run.rb
@@ -5,4 +5,7 @@
 input = File.read('./input.txt')
 
 ad = Advent::Pulses.new(input)
-puts "Part 1: #{ad.pulse_mult(1000)}"
\ No newline at end of file
+puts "Part 1: #{ad.pulse_mult(1000)}"
+
+ad = Advent::Pulses.new(input)
+puts "Part 2: #{ad.rx_cycles}"
\ No newline at end of file
diff --git a/2023/20/spec/pulses_spec.rb b/2023/20/spec/pulses_spec.rb
index 03086f0..2c14cf7 100644
--- a/2023/20/spec/pulses_spec.rb
+++ b/2023/20/spec/pulses_spec.rb
@@ -110,7 +110,7 @@
 
     describe "#button!" do
       it "sends a broadcast pulse" do
-        expect(ad).to receive(:send_pulse).with('broadcaster', 'button', 0)
+        expect(ad).to receive(:send_pulse).with('broadcaster', 'button', 0, anything, anything)
         ad.button!
         expect(ad.state['a']).to eq(0)
         expect(ad.state['b']).to eq(0)
@@ -180,14 +180,13 @@
       end
     end
 
-# button -low-> broadcaster
-# broadcaster -low-> a
-# a -low-> inv
-# a -low-> con
-# inv -high-> b
-# con -high-> output
+    describe "#rx_cycles" do
+      let(:input) { File.read('./input.txt') }
 
-    context "validation" do
+      it "returns the number of cycles to send a low pulse to rx" do
+        # ad.debug!
+        expect(ad.rx_cycles).to eq(244178746156661)
+      end
     end
   end
 end