229 lines
7.9 KiB
Plaintext
229 lines
7.9 KiB
Plaintext
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Advent of Code
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--- Day 12: Garden Groups ---
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Why not search for the Chief Historian near the [16]gardener and his
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[17]massive farm? There's plenty of food, so The Historians grab something
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to eat while they search.
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You're about to settle near a complex arrangement of garden plots when
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some Elves ask if you can lend a hand. They'd like to set up fences around
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each region of garden plots, but they can't figure out how much fence they
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need to order or how much it will cost. They hand you a map (your puzzle
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input) of the garden plots.
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Each garden plot grows only a single type of plant and is indicated by a
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single letter on your map. When multiple garden plots are growing the same
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type of plant and are touching (horizontally or vertically), they form a
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region. For example:
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AAAA
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BBCD
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BBCC
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EEEC
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This 4x4 arrangement includes garden plots growing five different types of
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plants (labeled A, B, C, D, and E), each grouped into their own region.
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In order to accurately calculate the cost of the fence around a single
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region, you need to know that region's area and perimeter.
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The area of a region is simply the number of garden plots the region
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contains. The above map's type A, B, and C plants are each in a region of
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area 4. The type E plants are in a region of area 3; the type D plants are
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in a region of area 1.
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Each garden plot is a square and so has four sides. The perimeter of a
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region is the number of sides of garden plots in the region that do not
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touch another garden plot in the same region. The type A and C plants are
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each in a region with perimeter 10. The type B and E plants are each in a
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region with perimeter 8. The lone D plot forms its own region with
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perimeter 4.
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Visually indicating the sides of plots in each region that contribute to
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the perimeter using - and |, the above map's regions' perimeters are
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measured as follows:
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+-+-+-+-+
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|A A A A|
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+-+-+-+-+ +-+
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|D|
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+-+-+ +-+ +-+
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|B B| |C|
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+ + + +-+
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|B B| |C C|
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+-+-+ +-+ +
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|C|
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+-+-+-+ +-+
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|E E E|
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+-+-+-+
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Plants of the same type can appear in multiple separate regions, and
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regions can even appear within other regions. For example:
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OOOOO
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OXOXO
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OOOOO
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OXOXO
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OOOOO
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The above map contains five regions, one containing all of the O garden
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plots, and the other four each containing a single X plot.
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The four X regions each have area 1 and perimeter 4. The region containing
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21 type O plants is more complicated; in addition to its outer edge
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contributing a perimeter of 20, its boundary with each X region
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contributes an additional 4 to its perimeter, for a total perimeter of 36.
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Due to "modern" business practices, the price of fence required for a
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region is found by multiplying that region's area by its perimeter. The
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total price of fencing all regions on a map is found by adding together
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the price of fence for every region on the map.
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In the first example, region A has price 4 * 10 = 40, region B has price 4
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* 8 = 32, region C has price 4 * 10 = 40, region D has price 1 * 4 = 4,
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and region E has price 3 * 8 = 24. So, the total price for the first
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example is 140.
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In the second example, the region with all of the O plants has price 21 *
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36 = 756, and each of the four smaller X regions has price 1 * 4 = 4, for
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a total price of 772 (756 + 4 + 4 + 4 + 4).
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Here's a larger example:
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RRRRIICCFF
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RRRRIICCCF
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VVRRRCCFFF
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VVRCCCJFFF
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VVVVCJJCFE
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VVIVCCJJEE
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VVIIICJJEE
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MIIIIIJJEE
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MIIISIJEEE
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MMMISSJEEE
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It contains:
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• A region of R plants with price 12 * 18 = 216.
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• A region of I plants with price 4 * 8 = 32.
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• A region of C plants with price 14 * 28 = 392.
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• A region of F plants with price 10 * 18 = 180.
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• A region of V plants with price 13 * 20 = 260.
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• A region of J plants with price 11 * 20 = 220.
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• A region of C plants with price 1 * 4 = 4.
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• A region of E plants with price 13 * 18 = 234.
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• A region of I plants with price 14 * 22 = 308.
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• A region of M plants with price 5 * 12 = 60.
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• A region of S plants with price 3 * 8 = 24.
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So, it has a total price of 1930.
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What is the total price of fencing all regions on your map?
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Your puzzle answer was 1522850.
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--- Part Two ---
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Fortunately, the Elves are trying to order so much fence that they qualify
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for a bulk discount!
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Under the bulk discount, instead of using the perimeter to calculate the
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price, you need to use the number of sides each region has. Each straight
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section of fence counts as a side, regardless of how long it is.
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Consider this example again:
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AAAA
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BBCD
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BBCC
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EEEC
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The region containing type A plants has 4 sides, as does each of the
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regions containing plants of type B, D, and E. However, the more complex
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region containing the plants of type C has 8 sides!
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Using the new method of calculating the per-region price by multiplying
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the region's area by its number of sides, regions A through E have prices
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16, 16, 32, 4, and 12, respectively, for a total price of 80.
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The second example above (full of type X and O plants) would have a total
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price of 436.
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Here's a map that includes an E-shaped region full of type E plants:
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EEEEE
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EXXXX
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EEEEE
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EXXXX
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EEEEE
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The E-shaped region has an area of 17 and 12 sides for a price of 204.
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Including the two regions full of type X plants, this map has a total
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price of 236.
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This map has a total price of 368:
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AAAAAA
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AAABBA
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AAABBA
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ABBAAA
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ABBAAA
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AAAAAA
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It includes two regions full of type B plants (each with 4 sides) and a
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single region full of type A plants (with 4 sides on the outside and 8
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more sides on the inside, a total of 12 sides). Be especially careful when
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counting the fence around regions like the one full of type A plants; in
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particular, each section of fence has an in-side and an out-side, so the
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fence does not connect across the middle of the region (where the two B
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regions touch diagonally). (The Elves would have used the Möbius Fencing
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Company instead, but their contract terms were too one-sided.)
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The larger example from before now has the following updated prices:
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• A region of R plants with price 12 * 10 = 120.
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• A region of I plants with price 4 * 4 = 16.
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• A region of C plants with price 14 * 22 = 308.
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• A region of F plants with price 10 * 12 = 120.
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• A region of V plants with price 13 * 10 = 130.
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• A region of J plants with price 11 * 12 = 132.
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• A region of C plants with price 1 * 4 = 4.
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• A region of E plants with price 13 * 8 = 104.
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• A region of I plants with price 14 * 16 = 224.
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• A region of M plants with price 5 * 6 = 30.
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• A region of S plants with price 3 * 6 = 18.
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Adding these together produces its new total price of 1206.
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What is the new total price of fencing all regions on your map?
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Your puzzle answer was 953738.
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Both parts of this puzzle are complete! They provide two gold stars: **
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At this point, you should [18]return to your Advent calendar and try
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another puzzle.
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If you still want to see it, you can [19]get your puzzle input.
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References
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Visible links
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1. https://adventofcode.com/
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2. https://adventofcode.com/2024/about
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3. https://adventofcode.com/2024/events
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4. https://cottonbureau.com/people/advent-of-code
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5. https://adventofcode.com/2024/settings
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6. https://adventofcode.com/2024/auth/logout
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7. Advent of Code Supporter
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https://adventofcode.com/2024/support
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8. https://adventofcode.com/2024
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9. https://adventofcode.com/2024
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10. https://adventofcode.com/2024/support
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12. https://adventofcode.com/2024/leaderboard
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13. https://adventofcode.com/2024/stats
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16. https://adventofcode.com/2023/day/5
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17. https://adventofcode.com/2023/day/21
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18. https://adventofcode.com/2024
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19. https://adventofcode.com/2024/day/12/input
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