Day 18

Author: petertseng

18_duet.rb

@@ -0,0 +1,64 @@
+def run(insts, id, tx, rx)
+  regs = Hash.new(0)
+  regs[:p] = id
+  vals_received = 0
+  pc = 0
+  resolve = ->(y) { y.is_a?(Integer) ? y : regs[y] }
+
+  -> {
+    ran_anything = false
+
+    while pc >= 0 && (inst = insts[pc])
+      case inst[0]
+      when :snd
+        tx << resolve[inst[1]]
+      when :set
+        regs[inst[1]] = resolve[inst[2]]
+      when :add
+        regs[inst[1]] += resolve[inst[2]]
+      when :mul
+        regs[inst[1]] *= resolve[inst[2]]
+      when :mod
+        regs[inst[1]] %= resolve[inst[2]]
+      when :rcv
+        if tx.object_id == rx.object_id
+          # Part 1!
+          return rx[-1] if resolve[inst[1]] != 0
+        else
+          # Part 2!
+          return ran_anything ? :wait : :still_waiting unless (val = rx[vals_received])
+          vals_received += 1
+          regs[inst[1]] = val
+        end
+      when :jgz
+        pc += (resolve[inst[2]] - 1) if resolve[inst[1]] > 0
+      else raise "Unknown instruction #{inst}"
+      end
+
+      pc += 1
+      ran_anything = true
+    end
+
+    :finished
+  }
+end
+
+insts = ARGF.map { |l|
+  inst, *args = l.split
+  [inst.to_sym, *args.map { |a| a.match?(/-?\d+/) ? a.to_i : a.to_sym }].freeze
+}.freeze
+
+sound = []
+puts run(insts, 0, sound, sound)[]
+
+send = [[], []]
+runners = [0, 1].map { |id| run(insts, id, send[id], send[1 - id]) }
+other_was_waiting = false
+puts 0.step { |n|
+  status = runners[n % 2][]
+  if status == :still_waiting && other_was_waiting
+    # Deadlocked.
+    break send[1].size
+  end
+  other_was_waiting = status == :still_waiting
+}