Solve day 12

12_potplants.py

@@ -0,0 +1,25 @@
+#!/usr/bin/env python3
+import sys
+
+initial = sys.stdin.readline().split()[-1].replace('.', ' ')
+sys.stdin.readline()
+trans = dict(tuple(line.rstrip().replace('.', ' ').split(' => '))
+             for line in sys.stdin)
+
+def spread(iters):
+    offset = 0
+    pattern = initial
+    for i in range(iters):
+        pattern = '    ' + pattern + '    '
+        leftpad = ''.join(trans.get(pattern[i - 2: i + 3], ' ')
+                          for i in range(2, len(pattern) - 2)).rstrip()
+        stripped = leftpad.lstrip()
+        offset += len(leftpad) - len(stripped) - 2
+        pattern = stripped
+    return sum(i + offset for i, c in enumerate(pattern) if c == '#')
+
+print(spread(20))
+n = 500
+a = spread(n)
+b = spread(n + 1)
+print(a + (b - a) * (50000000000 - n))

input/12

@@ -0,0 +1,34 @@
+initial state: ######....##.###.#..#####...#.#.....#..#.#.##......###.#..##..#..##..#.##..#####.#.......#.....##..
+
+...## => #
+###.. => .
+#.#.# => .
+##### => .
+....# => .
+##.## => .
+##.#. => #
+##... => #
+#..#. => #
+#.#.. => .
+#.##. => .
+..... => .
+##..# => .
+#..## => .
+.##.# => #
+..### => #
+..#.# => #
+.#### => #
+.##.. => .
+.#..# => #
+..##. => .
+#.... => .
+#...# => .
+.###. => .
+..#.. => .
+####. => #
+.#.## => .
+###.# => .
+#.### => #
+.#... => #
+.#.#. => .
+...#. => .