From 7cadfc7ce07f30f21447f3a1b748af8a59cf0703 Mon Sep 17 00:00:00 2001
From: Marcin Chrzanowski <marcin.j.chrzanowski@gmail.com>
Date: Fri, 25 Dec 2020 15:31:15 +0100
Subject: Add day 14

---
 14/b.rb | 58 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 58 insertions(+)
 create mode 100644 14/b.rb

(limited to '14/b.rb')

diff --git a/14/b.rb b/14/b.rb
new file mode 100644
index 0000000..e70c756
--- /dev/null
+++ b/14/b.rb
@@ -0,0 +1,58 @@
+def mask_address address, mask 
+  address.chars.zip(mask.chars).map do |bit, mask_bit|
+    case mask_bit
+    when '0'
+      bit
+    when '1'
+      '1'
+    when 'X'
+      'X'
+    end
+  end.join ''
+end
+lines = File.readlines('input.txt')
+
+mask = ''
+
+code = []
+
+lines.each do |line|
+  if line.slice(0, 4) == 'mask'
+    mask = line.split(' = ')[1].strip
+  else
+    split = line.split(/\[|\] = /)
+    address = split[1].to_i.to_s(2).rjust 36, '0'
+    value = split[2].to_i
+    code.push [mask_address(address, mask), value]
+  end
+end
+
+def enumerate_addresses address
+  first_x = address.index 'X'
+  if !first_x
+    return [address]
+  end
+  first_segment = address.slice(0, first_x)
+  rest = address.slice(first_x + 1, address.length)
+  enumerate_addresses(rest).flat_map do |a|
+    [
+      (first_segment + '0' + a),
+      (first_segment + '1' + a)
+    ]
+  end
+end
+
+mem = Hash.new 0
+code.each do |address, value|
+  addresses = enumerate_addresses address 
+  addresses.each do |a|
+    mem[a] = value
+  end
+end
+
+sum = 0
+mem.each_value do |v|
+  sum += v
+end
+
+puts sum
-- 
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