From 67d468a613bd6e20b2e9607f350bc0878e2ae8d8 Mon Sep 17 00:00:00 2001
From: Nat Lasseter <user@4574.co.uk>
Date: Wed, 5 Dec 2018 10:38:42 +0000
Subject: [day05] made it fast with barrucadu's suggestion

---
 day05/part1 | 31 +++++++++++++------------------
 day05/part2 | 30 +++++++++++++-----------------
 2 files changed, 26 insertions(+), 35 deletions(-)

diff --git a/day05/part1 b/day05/part1
index 4761380..9fe581d 100755
--- a/day05/part1
+++ b/day05/part1
@@ -2,26 +2,21 @@
 
 input = gets.chomp.chars
 
-l = input.length
-loop do
-  i = input.length - 1
-  loop do
-    break if i < 1
+polymer = input
+nextpolymer = Array.new(polymer.length)
+nextpolymer[0] = polymer[0]
+index = 1
+nextindex = 0
 
-    if input[i] == input[i-1].swapcase
-      input[i] = nil
-      input[i-1] = nil
-      i -= 2
-    else
-      i -= 1
-    end
-  end
-  input = input.compact
-  if input.length == l
-    break
+while index < polymer.length do
+  if polymer[index].swapcase != nextpolymer[nextindex]
+    nextindex += 1
+    nextpolymer[nextindex] = polymer[index]
   else
-    l = input.length
+    nextpolymer[nextindex] = nil
+    nextindex -= 1
   end
+  index += 1
 end
 
-puts input.length
+puts nextpolymer.compact.length
diff --git a/day05/part2 b/day05/part2
index b71d84e..d09ff86 100755
--- a/day05/part2
+++ b/day05/part2
@@ -8,27 +8,23 @@ lengths = {}
 units.each do |unit|
   polymer = input.dup
   polymer.delete_if {|u| u == unit || u == unit.upcase}
-  l = polymer.length
-  loop do
-    i = polymer.length - 1
-    loop do
-      break if i < 1
+  nextpolymer = Array.new(polymer.length)
+  nextpolymer[0] = polymer[0]
+  index = 1
+  nextindex = 0
 
-      if polymer[i] == polymer[i-1].swapcase
-        polymer.delete_at(i)
-        polymer.delete_at(i-1)
-        i -= 2
-      else
-        i -= 1
-      end
-    end
-    if polymer.length == l
-      break
+  while index < polymer.length do
+    if polymer[index].swapcase != nextpolymer[nextindex]
+      nextindex += 1
+      nextpolymer[nextindex] = polymer[index]
     else
-      l = polymer.length
+      nextpolymer[nextindex] = nil
+      nextindex -= 1
     end
+    index += 1
   end
-  lengths[unit] = polymer.length
+
+  lengths[unit] = nextpolymer.compact.length
 end
 
 puts lengths.values.min
-- 
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