Day twenty-two

22/main.rb

@@ -0,0 +1,53 @@
+#!/usr/bin/env ruby
+
+require "debug"
+
+input = (ARGV.first.nil? ? DATA : ARGF)
+  .readlines(chomp: true)
+  .map(&:to_i)
+
+def evolve(secret)
+  a = ((secret * 64) ^ secret) % 16777216
+  b = ((a / 32) ^ a) % 16777216
+  c = ((b * 2048) ^ b) % 16777216
+end
+
+part_1 = input.map do |secret|
+  original = secret
+  2000.times { secret = evolve(secret) }
+
+  secret
+end.sum
+
+p part_1
+
+sequences = input.map do |secret|
+  secrets = 2000.times
+    .map { secret = evolve(secret) }
+
+  prices = secrets.map { _1.digits.first }
+
+  changes = prices
+    .map.with_index { |p, i| i == 0 ? 0 : p - prices[i - 1] }
+
+  sequences = Hash.new
+  changes[1..].each_cons(4).with_index.each do |sequence, i|
+    sequences[sequence] ||= prices[i + 4]
+  end
+
+  sequences
+end
+
+unique_sequences = sequences.flat_map(&:keys).uniq
+
+part_2 = unique_sequences.map do |sequence|
+  sequences.sum { _1.fetch(sequence, 0) }
+end.max
+
+p part_2
+
+__END__
+1
+10
+100
+2024