2018 day 12 done

2018/day12/problem

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+Advent of Code
+
+--- Day 12: Subterranean Sustainability ---
+
+   The year 518 is significantly more underground than your history books implied. Either that, or you've arrived in a vast
+   cavern network under the North Pole.
+
+   After exploring a little, you discover a long tunnel that contains a row of small pots as far as you can see to your left
+   and right. A few of them contain plants - someone is trying to grow things in these geothermally-heated caves.
+
+   The pots are numbered, with 0 in front of you. To the left, the pots are numbered -1, -2, -3, and so on; to the right, 1, 2,
+   3.... Your puzzle input contains a list of pots from 0 to the right and whether they do (#) or do not (.) currently contain
+   a plant, the initial state. (No other pots currently contain plants.) For example, an initial state of #..##.... indicates
+   that pots 0, 3, and 4 currently contain plants.
+
+   Your puzzle input also contains some notes you find on a nearby table: someone has been trying to figure out how these
+   plants spread to nearby pots. Based on the notes, for each generation of plants, a given pot has or does not have a plant
+   based on whether that pot (and the two pots on either side of it) had a plant in the last generation. These are written as
+   LLCRR => N, where L are pots to the left, C is the current pot being considered, R are the pots to the right, and N is
+   whether the current pot will have a plant in the next generation. For example:
+
+     • A note like ..#.. => . means that a pot that contains a plant but with no plants within two pots of it will not have a
+       plant in it during the next generation.
+     • A note like ##.## => . means that an empty pot with two plants on each side of it will remain empty in the next
+       generation.
+     • A note like .##.# => # means that a pot has a plant in a given generation if, in the previous generation, there were
+       plants in that pot, the one immediately to the left, and the one two pots to the right, but not in the ones immediately
+       to the right and two to the left.
+
+   It's not clear what these plants are for, but you're sure it's important, so you'd like to make sure the current
+   configuration of plants is sustainable by determining what will happen after 20 generations.
+
+   For example, given the following input:
+
+ initial state: #..#.#..##......###...###
+
+ ...## => #
+ ..#.. => #
+ .#... => #
+ .#.#. => #
+ .#.## => #
+ .##.. => #
+ .#### => #
+ #.#.# => #
+ #.### => #
+ ##.#. => #
+ ##.## => #
+ ###.. => #
+ ###.# => #
+ ####. => #
+
+   For brevity, in this example, only the combinations which do produce a plant are listed. (Your input includes all possible
+   combinations.) Then, the next 20 generations will look like this:
+
+                  1         2         3
+        0         0         0         0
+  0: ...#..#.#..##......###...###...........
+  1: ...#...#....#.....#..#..#..#...........
+  2: ...##..##...##....#..#..#..##..........
+  3: ..#.#...#..#.#....#..#..#...#..........
+  4: ...#.#..#...#.#...#..#..##..##.........
+  5: ....#...##...#.#..#..#...#...#.........
+  6: ....##.#.#....#...#..##..##..##........
+  7: ...#..###.#...##..#...#...#...#........
+  8: ...#....##.#.#.#..##..##..##..##.......
+  9: ...##..#..#####....#...#...#...#.......
+ 10: ..#.#..#...#.##....##..##..##..##......
+ 11: ...#...##...#.#...#.#...#...#...#......
+ 12: ...##.#.#....#.#...#.#..##..##..##.....
+ 13: ..#..###.#....#.#...#....#...#...#.....
+ 14: ..#....##.#....#.#..##...##..##..##....
+ 15: ..##..#..#.#....#....#..#.#...#...#....
+ 16: .#.#..#...#.#...##...#...#.#..##..##...
+ 17: ..#...##...#.#.#.#...##...#....#...#...
+ 18: ..##.#.#....#####.#.#.#...##...##..##..
+ 19: .#..###.#..#.#.#######.#.#.#..#.#...#..
+ 20: .#....##....#####...#######....#.#..##.
+
+   The generation is shown along the left, where 0 is the initial state. The pot numbers are shown along the top, where 0
+   labels the center pot, negative-numbered pots extend to the left, and positive pots extend toward the right. Remember, the
+   initial state begins at pot 0, which is not the leftmost pot used in this example.
+
+   After one generation, only seven plants remain. The one in pot 0 matched the rule looking for ..#.., the one in pot 4
+   matched the rule looking for .#.#., pot 9 matched .##.., and so on.
+
+   In this example, after 20 generations, the pots shown as # contain plants, the furthest left of which is pot -2, and the
+   furthest right of which is pot 34. Adding up all the numbers of plant-containing pots after the 20th generation produces
+   325.
+
+   After 20 generations, what is the sum of the numbers of all pots which contain a plant?
+
+   Your puzzle answer was 2281.
+
+--- Part Two ---
+
+   You realize that 20 generations aren't enough. After all, these plants will need to last another 1500 years to even reach
+   your timeline, not to mention your future.
+
+   After fifty billion (50000000000) generations, what is the sum of the numbers of all pots which contain a plant?
+
+   Your puzzle answer was 2250000000120.
+
+   Both parts of this puzzle are complete! They provide two gold stars: **
+
+References
+
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+   . https://adventofcode.com/2018
+   . https://adventofcode.com/2018/day/12/input