Solution for Day 14

day_14/second.rb

@@ -0,0 +1,49 @@
+# frozen_string_literal: true
+
+input = File.readlines('./input').map(&:strip)
+$mask = ''
+$mem = {}
+
+def set_mask(mask)
+  _, $mask = mask.split(' = ')
+end
+
+def apply_mask(num)
+  bin = '%036b' % num
+  $mask.chars.each_with_index do |bit, i|
+    next if bit == '0'
+
+    bin[i] = bit
+  end
+  bin
+end
+
+def get_indices(index)
+  return [index] if index.count('X') == 0
+
+  idx = index.index 'X'
+  left = index
+  right = left.dup
+  left[idx] = '0'
+  right[idx] = '1'
+  [*get_indices(left), *get_indices(right)]
+end
+
+def run(cmd)
+  _, index, val = *cmd.match(/\Amem\[(\d+)\] = (\d+)\z/)
+  index = Integer(index)
+  val = Integer(val)
+
+  index = apply_mask(index)
+  indices = get_indices(index)
+  indices.each do |idx|
+    $mem[idx] = val
+  end
+end
+
+input.each do |line|
+  (set_mask(line); next) if line.start_with? 'mask'
+  run(line)
+end
+
+puts $mem.values.sum