what.

2018/12.py

@@ -57,6 +57,23 @@ with open('data/12.txt') as f:
 pots = grow(initial, 20)
 print(f'Part 1: {sum(pots)}\n')
 
-pots = grow(initial, 5 * 10 ** 10, True)
-print(f'Part 2: {pots}\n')
 
+# find pattern and exploit
+first_stable = 0
+prev_gen = []
+for i in range(1, 1000):
+    current_gen = sorted(grow(initial, i))
+    if current_gen == [x + 1 for x in prev_gen]:
+        first_stable = i - 1
+        break
+    else:
+        prev_gen = current_gen
+magic_number = sum(prev_gen)
+
+
+def cheat(num_gens):
+    if num_gens < first_stable:
+        raise RuntimeError("Can't cheat.")
+    return magic_number + (num_gens - first_stable) * len(prev_gen)
+
+print(f'Part 2: {cheat(5 * 10 ** 10)}\n')