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@@ -2,33 +2,43 @@ 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.
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.
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.
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:
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.
• 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.
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:
@@ -49,8 +59,9 @@ Advent of Code
###.# => #
####. => #
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:
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
@@ -76,27 +87,34 @@ Advent of Code
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.
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.
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.
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?
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.
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?
After fifty billion (50000000000) generations, what is the sum of the
numbers of all pots which contain a plant?
Your puzzle answer was 2250000000120.