From 402edd8b37e849e408f689763b9a9748dc6884c2 Mon Sep 17 00:00:00 2001
From: Jeremy Kaplan <jdkaplan@metagram.net>
Date: Sun, 8 Dec 2019 21:23:58 -0800
Subject: [PATCH] 2019: Day 7 Part 2

---
 2019/day7/intcode.rb | 10 ++++++-
 2019/day7/part2.rb   | 68 ++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 77 insertions(+), 1 deletion(-)
 create mode 100644 2019/day7/part2.rb

diff --git a/2019/day7/intcode.rb b/2019/day7/intcode.rb
index c0fd23e..5a6a0ae 100644
--- a/2019/day7/intcode.rb
+++ b/2019/day7/intcode.rb
@@ -84,20 +84,27 @@ module Intcode
       case operation(@mem[@ip])
       when 1
         add!
+        nil
       when 2
         mul!
+        nil
       when 3
         input!(&@input_block)
+        nil
       when 4
         output!(&@output_block)
       when 5
         branch_if_not_zero!
+        nil
       when 6
         branch_if_zero!
+        nil
       when 7
         less_than!
+        nil
       when 8
         equal!
+        nil
       when 99
         :done_executing
       else
@@ -143,6 +150,7 @@ module Intcode
       output = read(@ip + 1, mode[0])
       user_output.call output if block_given?
       @ip += 2
+      output
     end
 
     def branch_if_not_zero!
@@ -184,7 +192,7 @@ module Intcode
     def input
       if block_given?
         inp = yield
-        raise "Invalid input: #{inp}" unless inp.is_a?(Numeric)
+        raise "Invalid input: #{inp.inspect}" unless inp.is_a?(Numeric)
 
         return inp
       end
diff --git a/2019/day7/part2.rb b/2019/day7/part2.rb
new file mode 100644
index 0000000..218bb06
--- /dev/null
+++ b/2019/day7/part2.rb
@@ -0,0 +1,68 @@
+# frozen_string_literal: true
+
+require_relative 'intcode'
+
+def inputter(queue)
+  idx = 0
+  proc do
+    input = queue[idx]
+    idx += 1
+    input
+  end
+end
+
+class Amplifier
+  def initialize(memory, phase)
+    @input_queue = [phase]
+    @computer = Intcode::Computer.new(memory) { @input_queue.shift }
+  end
+
+  def amplify(input)
+    @input_queue << input
+    output = nil
+    output = @computer.tick until output
+    output
+  end
+
+  def input(val)
+    @input_queue << val
+  end
+end
+
+def thrust(program, phases)
+  a = Amplifier.new(program.as_memory, phases[0])
+  b = Amplifier.new(program.as_memory, phases[1])
+  c = Amplifier.new(program.as_memory, phases[2])
+  d = Amplifier.new(program.as_memory, phases[3])
+  e = Amplifier.new(program.as_memory, phases[4])
+
+  cache = -Float::INFINITY
+  out1 = a.amplify(0)
+  loop do
+    out2 = b.amplify(out1)
+    out3 = c.amplify(out2)
+    out4 = d.amplify(out3)
+    out5 = e.amplify(out4)
+    return cache if out5 == :done_executing
+
+    cache = out5
+    out1 = a.amplify(out5)
+  end
+end
+
+program = Intcode.read(File.join(__dir__, 'input'))
+
+phase_space = [5, 6, 7, 8, 9].permutation(5)
+
+max_thrust = -Float::INFINITY
+max_phases = nil
+phase_space.each do |phases|
+  t = thrust(program, phases)
+  next unless t > max_thrust
+
+  max_thrust = t
+  max_phases = phases
+end
+
+pp max_phases
+puts max_thrust