Day eleven

11/input

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+4 4841539 66 5279 49207 134 609568 0

11/main.rb

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+#!/usr/bin/env ruby
+
+require "debug"
+
+input = (ARGV.first.nil? ? DATA : ARGF)
+  .read
+  .split(/\s+/)
+  .map(&:to_i)
+
+@cache = Hash.new
+
+def recursive_transform(stone, blinks = 0)
+  if blinks.zero?
+    return 1
+  elsif @cache[[blinks, stone]]
+    return @cache[[blinks, stone]]
+  elsif stone.zero?
+    res = recursive_transform(1, blinks - 1)
+  elsif stone.digits.size.even?
+    stone = stone.to_s
+    mid = stone.size / 2
+    res = [
+      recursive_transform(stone[...mid].to_i, blinks - 1),
+      recursive_transform(stone[mid..].to_i, blinks - 1)
+    ].sum
+  else
+    res = recursive_transform(stone * 2024, blinks - 1)
+  end
+
+  @cache[[blinks, stone]] = res
+end
+
+p input.map { recursive_transform(_1, 75) }.sum
+
+__END__
+125 17