diff --git a/17/main.rb b/17/main.rb
index 2068955..07fd227 100755
--- a/17/main.rb
+++ b/17/main.rb
@@ -20,22 +20,21 @@ program = input[split+1]
   .split(",")
   .map(&:to_i)
 
-OPERANDS = [
-  ->() { 0 }, ->() { 1 }, ->() { 2 }, ->() { 3 },
-  ->() { registers[:A] },
-  ->() { registers[:B] },
-  ->() { registers[:C] },
-  ->() { :noop },
-]
-
 def execute(registers, program)
   stdout, commands = Array.new, Array.new
+  operands = [
+    ->() { 0 }, ->() { 1 }, ->() { 2 }, ->() { 3 },
+    ->() { registers[:A] },
+    ->() { registers[:B] },
+    ->() { registers[:C] },
+    ->() { :noop },
+  ]
 
   ic = 0
   while ic < program.size
     opcode = program[ic]
     literal_operand = program[ic+1]
-    combo_operand = OPERANDS[literal_operand].call
+    combo_operand = operands[literal_operand].call
 
     ic += 2
 
@@ -84,25 +83,37 @@ def execute(registers, program)
   [registers, program, stdout.join(",")]
 end
 
-part_2 = registers[:A].dup
-_, _, part_1 = execute(registers, program)
+_, _, part_1 = execute(registers.dup, program)
 p part_1
 
-while true
-  part_2 += 100_00
-  registers = {A: part_2, B: 0, C: 0}
-  _, _, output = execute(registers, program)
-  p "#{part_2} (a): #{output}"
-  break if output.match?(/4,1,5,5,0,3,3,0$/)
+
+def reverse_engineer(program, slot, i)
+  candidates = (0..8).map do |i|
+    [i, execute({A: i, B: 0, C: 0}, program).last.split(",").map(&:to_i)
+    ]
+  end.select { _1.last == program[slot..] }
 end
 
-while part_2 <<= 3
-  registers = {A: part_2, B: 0, C: 0}
-  _, _, output = execute(registers, program)
+part_2 = 0
+(program.size - 1).downto(0) do |slot|
+  candidates = []
+  (0..8).each do |i|
+    candidate = part_2 + i
+    _, _, output = execute({A: candidate, B: 0, C: 0}, program)
+    new_program = output.split(",").map(&:to_i)
 
-  next if output.size < 31
-  p "#{part_2} (b): #{output}"
-  raise if output.size > 31
+    if new_program == program[slot..]
+      candidates << candidate
+      unless [301,2566855701950, 20534845615581, 20534845615573, 20534845615583].include?(candidate)
+        part_2 = candidate
+      end
+    end
+  end
+  #p candidates
+  if slot == 0
+    p candidates.first
+  end
+  part_2 <<= 3
 end
 
 __END__