Part 1

17/input

@@ -0,0 +1,5 @@
+Register A: 17323786
+Register B: 0
+Register C: 0
+
+Program: 2,4,1,1,7,5,1,5,4,1,5,5,0,3,3,0

17/main.rb

@@ -0,0 +1,79 @@
+#!/usr/bin/env ruby
+
+require "debug"
+
+input = (ARGV.first.nil? ? DATA : ARGF)
+  .readlines(chomp: true)
+split = input.index("")
+
+registers = input[...split]
+  .map { _1.split(": ") }
+  .map(&:last)
+  .map(&:to_i)
+  .zip(%i[A B C])
+  .map(&:reverse)
+  .to_h
+program = input[split+1]
+  .split(" ")
+  .last
+  .split(",")
+  .map(&:to_i)
+
+OPERANDS = [
+  ->() { 0 }, ->() { 1 }, ->() { 2 }, ->() { 3 },
+  ->() { registers[:A] },
+  ->() { registers[:B] },
+  ->() { registers[:C] },
+  ->() { :noop },
+]
+
+stdout = []
+
+i = 0
+while i < program.size
+  opcode = program[i]
+  literal_operand = program[i+1]
+  combo_operand = OPERANDS[literal_operand].call
+
+  i += 2
+
+  case opcode
+  when 0
+    numerator = registers[:A]
+    denominator = 2 ** combo_operand
+    registers[:A] = numerator / denominator
+  when 1
+    registers[:B] = registers[:B] ^ literal_operand
+  when 2
+    registers[:B] = combo_operand % 8
+  when 3
+    if registers[:A] == 0
+      :noop
+    else
+      i = literal_operand
+    end
+  when 4
+    registers[:B] = registers[:B] ^ registers[:C]
+  when 5
+    stdout << combo_operand % 8
+  when 6
+    numerator = registers[:A]
+    denominator = 2 ** combo_operand
+    registers[:B] = numerator / denominator
+  when 7
+    numerator = registers[:A]
+    denominator = 2 ** combo_operand
+    registers[:C] = numerator / denominator
+  end
+end
+
+p registers
+
+puts stdout.join(",")
+
+__END__
+Register A: 729
+Register B: 0
+Register C: 0
+
+Program: 0,1,5,4,3,0