Add solution for day 12

Author: Simon Hessner

day12/example

@@ -0,0 +1,16 @@
+initial state: #..#.#..##......###...###
+
+...## => #
+..#.. => #
+.#... => #
+.#.#. => #
+.#.## => #
+.##.. => #
+.#### => #
+#.#.# => #
+#.### => #
+##.#. => #
+##.## => #
+###.. => #
+###.# => #
+####. => #

day12/input

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

day12/solution.py

@@ -0,0 +1,38 @@
+def find_match(rule, pots):
+	for i in range(len(pots)-5):
+		if pots[i:i+5] == rule:
+			return i+2
+	return None
+
+from collections import defaultdict
+
+def getsum(pots, first):
+	s = 0
+	for i,c in enumerate(pots):
+		if c == "#":
+			s += i - first
+	return s
+
+with open('input') as f:
+	lines = f.read().splitlines()
+	pots = lines[0].split(": ")[1]
+	pots = "."*20000 + pots + "."*20000
+	first = 0
+	for i,c in enumerate(pots):
+		if c == "#":
+			first = i
+			break
+		
+	rules = defaultdict(lambda : ".")
+	for rule in lines[2:]:
+		condition, replacement = rule.split(" => ")
+		rules[condition] = replacement
+
+	for g in range(200):
+		newpots = list(pots)
+		for i in range(2, len(pots)-2):
+			newpots[i] = rules[pots[i-2:i+3]]
+		pots = "".join(newpots)
+		s = getsum(pots, first)
+		
+	print((50000000000-200)*87+s)