diff --git a/2018/12.py b/2018/12.py
index a0f719a..12c2a9c 100644
--- a/2018/12.py
+++ b/2018/12.py
@@ -1,3 +1,6 @@
+import re
+
+
 def to_int(bitlist):
     out = 0
     for bit in bitlist:
@@ -5,37 +8,42 @@ def to_int(bitlist):
     return out
 
 
-def get_slice(index, pots):
-    for i in range(index - 2, index + 3):
-        if i < 0:
-            yield 0
-        yield pots[i]
-
-
-def grow(init, num_gens):
-    current_gen = init
+def grow(init, num_gens, progress=False):
+    first, last = min(init), max(init)
+    current_gen = set(init)
     for g in range(num_gens):
-        while current_gen[:2] != [0, 0]:
-            current_gen.insert(0, 0)
-        while current_gen[-2:] != [0, 0]:
-            current_gen.append(0)
-        
-        next_gen = []
-        for i, b in enumerate(current_gen):
-            key = to_int(get_slice(i, current_gen))
+        next_gen = set()
+        for i in range(first - 2, last + 3):
+            key = to_int(1 if b in current_gen else 0 for b in range(i - 2, i + 3))
             if key in positives:
-                next_gen.append(1)
-            else:
-                next_gen.append(0)
+                next_gen.add(i)
+                if i < first:
+                    first = i
+                if i > last:
+                    last = i
         current_gen = next_gen
 
+        if progress:
+            print('Generations:', g + 1, end='\r')
+
+    if progress: print('Generations:', g + 1)
     return current_gen
 
 
+def test(n):
+    pots = grow(initial, n)
+    first, last = min(pots), max(pots)
+    chars = []
+    for i in range(first - 1, last + 2):
+        chars.append('#' if i in pots else '.')
+    print(''.join(chars))
+
+
 with open('data/12.txt') as f:
-    initial = list(next(f)[15:-1])
-    initial = list(map(lambda p: int(p == '#'), initial))
+    initial = re.search('[#.]+', next(f)).group(0)
+    initial = {i for i, p in enumerate(initial) if p == '#'}
     next(f)
+    
     positives, negatives = set(), set()
     for line in f:
         state, result = line.strip().split(' => ')
@@ -46,7 +54,9 @@ with open('data/12.txt') as f:
             negatives.add(s)
 
 
-def test(n):
-    result = grow(initial, n)
-    print(''.join('#' if p else '.' for p in result))
+pots = grow(initial, 20)
+print(f'Part 1: {sum(pots)}\n')
+
+pots = grow(initial, 5 * 10 ** 10, True)
+print(f'Part 2: {pots}\n')
 
diff --git a/2018/data/test.txt b/2018/data/test.txt
new file mode 100644
index 0000000..8335d88
--- /dev/null
+++ b/2018/data/test.txt
@@ -0,0 +1,16 @@
+initial state: #..#.#..##......###...###
+
+...## => #
+..#.. => #
+.#... => #
+.#.#. => #
+.#.## => #
+.##.. => #
+.#### => #
+#.#.# => #
+#.### => #
+##.#. => #
+##.## => #
+###.. => #
+###.# => #
+####. => #
\ No newline at end of file