Year 2024 Day 11

2024/day11.rb

@@ -0,0 +1,25 @@
+stones = STDIN.read.split.map(&:to_i)
+
+def stone_count(stone, iterations, memo)
+  return 1 if iterations.zero?
+  return memo[[stone, iterations]] unless memo[[stone, iterations]].nil?
+
+  result = (
+    case
+    when stone == 0
+      stone_count(1, iterations - 1, memo)
+    when stone.to_s.size.even?
+      stone.to_s.chars.each_slice(stone.to_s.size / 2).map(&:join).map(&:to_i).map do |num|
+        stone_count(num, iterations - 1, memo)
+      end.sum
+    else
+      stone_count(stone * 2024, iterations - 1, memo)
+    end
+  )
+  memo[[stone, iterations]] = result
+  result
+end
+
+memo = {}
+puts stones.map { |stone| stone_count(stone, 25, memo) }.sum
+puts stones.map { |stone| stone_count(stone, 75, memo) }.sum

2024/examples/day11.txt

@@ -0,0 +1 @@
+125 17