From 2bb84ae6c6c71d51b445bf0b232c0eb6ca38e89b Mon Sep 17 00:00:00 2001
From: Nat Lasseter <user@4574.co.uk>
Date: Thu, 12 Dec 2019 12:13:56 +0000
Subject: Day 12 part 2, working, using the potentially bad assumption that the
 cycle contains the initial state

---
 day12/part2 | 38 +++++++++++++-------------------------
 1 file changed, 13 insertions(+), 25 deletions(-)

(limited to 'day12/part2')

diff --git a/day12/part2 b/day12/part2
index 237432f..f5b0f96 100755
--- a/day12/part2
+++ b/day12/part2
@@ -38,43 +38,31 @@ moonsz = input.map do |line|
   [m[2].to_i, 0]
 end
 
-xs = [moonsx.dup]
+initx = moonsx.map { |m| [m[0], m[1]] }
+xlen = 0
 loop do
   moonsx = apply_gravity(moonsx)
   moonsx = update(moonsx)
-  if xs.include?(moonsx) then
-    break
-  else
-    xs << moonsx.dup
-  end
+  xlen += 1
+  break if initx == moonsx
 end
-xintro = xs.index(moonsx)
-xlen = xs.count - xintro
 
-ys = [moonsy.dup]
+inity = moonsy.map { |m| [m[0], m[1]] }
+ylen = 0
 loop do
   moonsy = apply_gravity(moonsy)
   moonsy = update(moonsy)
-  if ys.include?(moonsy) then
-    break
-  else
-    ys << moonsy.dup
-  end
+  ylen += 1
+  break if inity == moonsy
 end
-yintro = ys.index(moonsy)
-ylen = ys.count - yintro
 
-zs = [moonsz.dup]
+initz = moonsz.map { |m| [m[0], m[1]] }
+zlen = 0
 loop do
   moonsz = apply_gravity(moonsz)
   moonsz = update(moonsz)
-  if zs.include?(moonsz) then
-    break
-  else
-    zs << moonsz.dup
-  end
+  zlen += 1
+  break if initz == moonsz
 end
-zintro = zs.index(moonsz)
-zlen = zs.count - zintro
 
-puts [xintro, yintro, zintro].max + [xlen, ylen, zlen].reduce(1, :lcm)
+puts [xlen, ylen, zlen].reduce(1, :lcm)
-- 
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