1 files changed, 95 insertions, 0 deletions
diff --git a/day18.rb b/day18.rb
new file mode 100644
index 0000000..a9f0967
--- /dev/null
+++ b/day18.rb
@@ -0,0 +1,95 @@
+d = ["\n", *File.readlines("day18").map { |x| " " + x }, "\n"]
+
+
+=begin
+    An open acre will become filled with trees if three or more adjacent acres contained trees. Otherwise, nothing happens.
+    An acre filled with trees will become a lumberyard if three or more adjacent acres were lumberyards. Otherwise, nothing happens.
+    An acre containing a lumberyard will remain a lumberyard if it was adjacent to at least one other lumberyard and at least one acre containing trees. Otherwise, it becomes open.
+=end
+
+
+xd = <<EOF.lines.to_a
+
+ .#.#...|#.
+ .....#|##|
+ .|..|...#.
+ ..|#.....#
+ #.#|||#|#|
+ ...#.||...
+ .|....|...
+ ||...#|.#|
+ |.||||..|.
+ ...#.|..|.
+
+EOF
+
+require 'pp'
+
+seen = []
+
+p1 = 0
+
+i = 0
+d2 = nil
+1000.times { |i|
+pp d
+
+d2 = d.map(&:clone)
+
+d.each_index { |i|
+  d[i].chars.each_index { |j|
+    case d[i][j]
+    when '.'
+      if [d[i-1][j-1], d[i-1][j], d[i-1][j+1],
+          d[i  ][j-1],            d[i  ][j+1],
+          d[i+1][j-1], d[i+1][j], d[i+1][j+1]].count('|') >= 3
+        d2[i][j] = '|'
+      end
+    when '|'
+      if [d[i-1][j-1], d[i-1][j], d[i-1][j+1],
+          d[i  ][j-1],            d[i  ][j+1],
+          d[i+1][j-1], d[i+1][j], d[i+1][j+1]].count('#') >= 3
+        d2[i][j] = '#'
+      end
+    when '#'
+      s = [d[i-1][j-1], d[i-1][j], d[i-1][j+1], :X,
+           d[i  ][j-1],            d[i  ][j+1], :Y,
+           d[i+1][j-1], d[i+1][j], d[i+1][j+1]]
+      if s.include?('#') && s.include?('|')
+        # keep
+      else
+        d2[i][j] = '.'
+      end
+    end
+  }
+}
+
+if seen.include? d2
+  p [:cycle, i, seen.size - seen.index(d2)]
+  break
+else
+  seen << d2
+end
+
+if i == 10
+  r = d.join
+  p1 = r.count('#') * r.count('|')   # 535522
+end
+
+d = d2
+r = d.join
+}
+
+
+p p1
+
+n = (1000000000-i)%(seen.size - seen.index(d2))
+
+p seen.map { |s|
+r = s.join
+p2 = r.count('#') * r.count('|')
+}.index(210160)
+
+#p p2
+
+# 210160