From 73ca0bca600c77b8821ff4924c2099bdaad8d6a9 Mon Sep 17 00:00:00 2001
From: Alpha Chen <alpha@kejadlen.dev>
Date: Mon, 7 Dec 2020 21:20:06 -0800
Subject: [PATCH] [2020][ruby][8.x]

---
 2020/ruby/day_08.rb | 55 +++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 55 insertions(+)
 create mode 100644 2020/ruby/day_08.rb

diff --git a/2020/ruby/day_08.rb b/2020/ruby/day_08.rb
new file mode 100644
index 0000000..494ac94
--- /dev/null
+++ b/2020/ruby/day_08.rb
@@ -0,0 +1,55 @@
+require "set"
+
+class Program
+  attr_reader :accumulator
+
+  def initialize(instructions)
+    @instructions = instructions
+    @accumulator = 0
+    @pc = 0
+  end
+
+  def run
+    seen = Set.new
+
+    loop do
+      break if @pc == @instructions.size
+
+      fail if seen.include?(@pc)
+      seen << @pc
+
+      op, arg = @instructions.fetch(@pc)
+      case op
+      when :acc
+        @accumulator += arg
+        @pc += 1
+      when :jmp
+        @pc += arg
+      when :nop
+        @pc += 1
+      else
+        fail
+      end
+    end
+  end
+end
+
+instructions = ARGF.read.scan(/(\w+) ([-+]\d+)/).map {|op,arg| [op.to_sym, arg.to_i] }
+uncorrupt = { nop: :jmp, jmp: :nop }
+(0...instructions.size).select {|i|
+  op, _ = instructions.fetch(i)
+  uncorrupt.has_key?(op)
+}.map {|i|
+  attempt = instructions.clone
+  instruction = attempt.fetch(i)
+  attempt[i] = [uncorrupt.fetch(instruction[0]), instruction[1]]
+  attempt
+}.each do |i|
+  program = Program.new(i)
+  begin
+    program.run
+  rescue
+    next
+  end
+  puts "accumulator: #{program.accumulator}"
+end