From 45212a6916d440abe70bcf7ea94f3a371f59d008 Mon Sep 17 00:00:00 2001
From: Alpha Chen <alpha@kejadlen.dev>
Date: Wed, 23 Dec 2020 09:34:21 -0800
Subject: [PATCH] [2020][ruby][23.1]

---
 2020/ruby/day_23.rb | 31 +++++++++++++++++++++++++++++++
 1 file changed, 31 insertions(+)
 create mode 100644 2020/ruby/day_23.rb

diff --git a/2020/ruby/day_23.rb b/2020/ruby/day_23.rb
new file mode 100644
index 0000000..6a4093f
--- /dev/null
+++ b/2020/ruby/day_23.rb
@@ -0,0 +1,31 @@
+cups = ARGF.read.chars.map(&:to_i)
+cups_range = Range.new(*cups.minmax)
+
+current = 0
+100.times do
+  current_value = cups.fetch(current % cups.size)
+
+  pickup_indices = 3.times.map {|i| (current + i + 1) % cups.size }
+  pickup = cups.values_at(*pickup_indices)
+  pickup_indices.sort.reverse.each do |i|
+    cups.delete_at(i)
+  end
+
+  dest_value = current_value - 1
+  until cups_range.cover?(dest_value) && !pickup.include?(dest_value)
+    dest_value -= 1
+    dest_value = cups_range.end unless cups_range.cover?(dest_value)
+  end
+
+
+  dest_index = cups.index(dest_value)
+
+  cups.insert(dest_index+1, *pickup)
+
+  current = cups.index(current_value)
+  current += 1
+  current %= cups.size
+end
+
+i = cups.index(1)
+p (cups[i+1..-1] + cups[0...i]).join