Day twenty-four Part two

24/main.rb

@@ -10,6 +10,46 @@ input[...split]
   .map { _1.split(": ") }
   .each { wires[_1] = _2.to_i }
 
+flipped = Set.new
+gates.select { _1.match?(/XOR/) }.each do |gate|
+  in1, op, in2, out = gate.scan(/([a-z0-9]{3}) ([A-Z]+) ([a-z0-9]{3}) -> ([a-z0-9]{3})/).first
+
+  if op == "XOR" && [in1, in2].map { _1[0] }.sort != %w[x y]
+    if !out.start_with?("z")
+      flipped << out
+    end
+  end
+end
+
+# 45 is a half adder
+(0..44).each do |num|
+  z = "z#{'%02d' % num}"
+  gate = gates.find { _1.match?(/#{z}$/) }
+  in1, op, in2, out = gate.scan(/([a-z0-9]{3}) ([A-Z]+) ([a-z0-9]{3}) -> ([a-z0-9]{3})/).first
+  if op != "XOR"
+    flipped << z
+  end
+end
+
+gates.select { _1.match?(/AND/) }.each do |gate|
+  in1, op, in2, out = gate.scan(/([a-z0-9]{3}) ([A-Z]+) ([a-z0-9]{3}) -> ([a-z0-9]{3})/).first
+
+  if [in1, in2].map { _1[0] }.sort == %w[x y] && in1 != "x00"
+    if gates.find { _1.match?(/#{out}/) && _1.match?(/ OR /) }.nil?
+      flipped << out
+    end
+  end
+end
+
+gates.select { _1.match?(/XOR/) }.each do |gate|
+  in1, op, in2, out = gate.scan(/([a-z0-9]{3}) ([A-Z]+) ([a-z0-9]{3}) -> ([a-z0-9]{3})/).first
+
+  if [in1, in2].map { _1[0] }.sort == %w[x y] && in1 != "x00" && in1 != "y00"
+    if gates.count { _1.match?(/#{out}/) && _1.match?(/ XOR /) } != 2
+      flipped << out
+    end
+  end
+end
 
 i = 0
 until gates.empty?
@@ -44,6 +84,8 @@ z = wires.select { _1.match?(/^z/) }.sort_by(&:first).map { _1.last.to_s }.rever
 zi = z.to_i(2)
 p zi
 
+p flipped.sort.join(",")
+
 __END__
 x00: 0
 x01: 1
@@ -64,4 +106,3 @@ x02 AND y02 -> z01
 x03 AND y03 -> z03
 x04 AND y04 -> z04
 x05 AND y05 -> z00
-