From 337fa5835be1374aebe52fcd509a81d04844c286 Mon Sep 17 00:00:00 2001
From: Alpha Chen <alpha.chen@gmail.com>
Date: Sun, 9 Dec 2018 14:55:24 -0800
Subject: [PATCH] [2018][ruby][09.2]

---
 2018/ruby/day_09.rb | 56 ++++++++++++++++++++++++++-------------------
 1 file changed, 33 insertions(+), 23 deletions(-)

diff --git a/2018/ruby/day_09.rb b/2018/ruby/day_09.rb
index 64f4068..2bcfea3 100644
--- a/2018/ruby/day_09.rb
+++ b/2018/ruby/day_09.rb
@@ -1,35 +1,45 @@
+Node = Struct.new(*%i[ value next prev ]) do
+  def to_s
+    out = [value]
+    current = self
+    loop do
+      current = current.next
+      break if current == self
+      out << current.value
+    end
+    out.join(" ")
+  end
+end
+
 ARGF.read.chomp =~ /(\d+) players; last marble is worth (\d+) points/
 num_players = $1.to_i
-num_marbles = $2.to_i
+num_marbles = $2.to_i * 100
 
-circle = []
-marbles = (0...num_marbles).to_a
+current = Node.new(0, nil, nil)
+current.next = current.prev = current
 
-zero = marbles.shift
-circle << zero
-
-current_marble_index = 0
 current_player = 0
-scores = Hash.new(0)
-
-until marbles.empty?
-  current_marble = marbles.shift
-
-  if current_marble % 23 == 0
-    scores[current_player] += current_marble
-    index = (current_marble_index - 7) % circle.size
-    scores[current_player] += circle.delete_at(index)
-    current_marble_index = index
+scores = Array.new(num_players, 0)
+
+(1...num_marbles).each do |marble|
+  if marble % 23 == 0
+    scores[current_player] += marble
+    7.times { current = current.prev }
+    scores[current_player] += current.value
+    current.next.prev = current.prev
+    current.prev.next = current.next
+    current = current.next
   else
-    index = (current_marble_index + 2) % circle.size - 1
-    index += 1 unless index == -1
-    circle.insert(index, current_marble)
-    current_marble_index = index % circle.size
+    current = current.next
+    current.next = Node.new(marble, current.next, current)
+    current = current.next
+    current.next.prev = current
   end
 
-  # puts "[#{current_player + 1}] #{circle.join(" ")}"
+  # puts "[#{current_player + 1}] #{current}"
+  puts marble if marble % 100000 == 0
 
   current_player = (current_player + 1) % num_players
 end
 
-p scores.max_by(&:last)
+p scores.max