Advent of Code

--- Day 18: Settlers of The North Pole ---

   On the outskirts of the North Pole base construction project, many Elves are
   collecting lumber.

   The lumber collection area is 50 acres by 50 acres; each acre can be either
   open ground (.), trees (|), or a lumberyard (#). You take a scan of the area
   (your puzzle input).

   Strange magic is at work here: each minute, the landscape looks entirely
   different. In exactly one minute, an open acre can fill with trees, a wooded
   acre can be converted to a lumberyard, or a lumberyard can be cleared to
   open ground (the lumber having been sent to other projects).

   The change to each acre is based entirely on the contents of that acre as
   well as the number of open, wooded, or lumberyard acres adjacent to it at
   the start of each minute. Here, "adjacent" means any of the eight acres
   surrounding that acre. (Acres on the edges of the lumber collection area
   might have fewer than eight adjacent acres; the missing acres aren't
   counted.)

   In particular:

     • An open acre will become filled with trees if three or more adjacent
     acres contained trees. Otherwise, nothing happens. • An acre filled with
     trees will become a lumberyard if three or more adjacent acres were
     lumberyards. Otherwise, nothing happens. • An acre containing a lumberyard
     will remain a lumberyard if it was adjacent to at least one other
     lumberyard and at least one acre containing trees. Otherwise, it becomes
     open.

   These changes happen across all acres simultaneously, each of them using the
   state of all acres at the beginning of the minute and changing to their new
   form by the end of that same minute. Changes that happen during the minute
   don't affect each other.

   For example, suppose the lumber collection area is instead only 10 by 10
   acres with this initial configuration:

 Initial state: .#.#...|#. .....#|##| .|..|...#. ..|#.....# #.#|||#|#|
 ...#.||... .|....|... ||...#|.#| |.||||..|. ...#.|..|.

 After 1 minute: .......##. ......|### .|..|...#. ..|#||...# ..##||.|#|
 ...#||||.. ||...|||.. |||||.||.| |||||||||| ....||..|.

 After 2 minutes: .......#.. ......|#.. .|.|||.... ..##|||..# ..###|||#|
 ...#|||||. |||||||||. |||||||||| |||||||||| .|||||||||

 After 3 minutes: .......#.. ....|||#.. .|.||||... ..###|||.# ...##|||#|
 .||##||||| |||||||||| |||||||||| |||||||||| ||||||||||

 After 4 minutes: .....|.#.. ...||||#.. .|.#||||.. ..###||||# ...###||#|
 |||##||||| |||||||||| |||||||||| |||||||||| ||||||||||

 After 5 minutes: ....|||#.. ...||||#.. .|.##||||. ..####|||# .|.###||#|
 |||###|||| |||||||||| |||||||||| |||||||||| ||||||||||

 After 6 minutes: ...||||#.. ...||||#.. .|.###|||. ..#.##|||# |||#.##|#|
 |||###|||| ||||#||||| |||||||||| |||||||||| ||||||||||

 After 7 minutes: ...||||#.. ..||#|##.. .|.####||. ||#..##||# ||##.##|#|
 |||####||| |||###|||| |||||||||| |||||||||| ||||||||||

 After 8 minutes: ..||||##.. ..|#####.. |||#####|. ||#...##|# ||##..###|
 ||##.###|| |||####||| ||||#||||| |||||||||| ||||||||||

 After 9 minutes: ..||###... .||#####.. ||##...##. ||#....### |##....##|
 ||##..###| ||######|| |||###|||| |||||||||| ||||||||||

 After 10 minutes: .||##..... ||###..... ||##...... |##.....## |##.....##
 |##....##| ||##.####| ||#####||| ||||#||||| ||||||||||

   After 10 minutes, there are 37 wooded acres and 31 lumberyards. Multiplying
   the number of wooded acres by the number of lumberyards gives the total
   resource value after ten minutes: 37 * 31 = 1147.

   What will the total resource value of the lumber collection area be after 10
   minutes?

   Your puzzle answer was 644640.

--- Part Two ---

   This important natural resource will need to last for at least thousands of
   years. Are the Elves collecting this lumber sustainably?

   What will the total resource value of the lumber collection area be after
   1000000000 minutes?

   Your puzzle answer was 191080.

   Both parts of this puzzle are complete! They provide two gold stars: **

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