118 lines
4.2 KiB
Plaintext
118 lines
4.2 KiB
Plaintext
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Advent of Code
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--- Day 11: Plutonian Pebbles ---
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The ancient civilization on [16]Pluto was known for its ability to
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manipulate spacetime, and while The Historians explore their infinite
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corridors, you've noticed a strange set of physics-defying stones.
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At first glance, they seem like normal stones: they're arranged in a
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perfectly straight line, and each stone has a number engraved on it.
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The strange part is that every time you blink, the stones change.
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Sometimes, the number engraved on a stone changes. Other times, a stone
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might split in two, causing all the other stones to shift over a bit to
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make room in their perfectly straight line.
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As you observe them for a while, you find that the stones have a
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consistent behavior. Every time you blink, the stones each simultaneously
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change according to the first applicable rule in this list:
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• If the stone is engraved with the number 0, it is replaced by a stone
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engraved with the number 1.
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• If the stone is engraved with a number that has an even number of
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digits, it is replaced by two stones. The left half of the digits are
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engraved on the new left stone, and the right half of the digits are
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engraved on the new right stone. (The new numbers don't keep extra
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leading zeroes: 1000 would become stones 10 and 0.)
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• If none of the other rules apply, the stone is replaced by a new
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stone; the old stone's number multiplied by 2024 is engraved on the
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new stone.
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No matter how the stones change, their order is preserved, and they stay
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on their perfectly straight line.
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How will the stones evolve if you keep blinking at them? You take a note
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of the number engraved on each stone in the line (your puzzle input).
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If you have an arrangement of five stones engraved with the numbers 0 1 10
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99 999 and you blink once, the stones transform as follows:
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• The first stone, 0, becomes a stone marked 1.
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• The second stone, 1, is multiplied by 2024 to become 2024.
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• The third stone, 10, is split into a stone marked 1 followed by a
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stone marked 0.
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• The fourth stone, 99, is split into two stones marked 9.
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• The fifth stone, 999, is replaced by a stone marked 2021976.
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So, after blinking once, your five stones would become an arrangement of
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seven stones engraved with the numbers 1 2024 1 0 9 9 2021976.
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Here is a longer example:
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Initial arrangement:
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125 17
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After 1 blink:
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253000 1 7
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After 2 blinks:
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253 0 2024 14168
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After 3 blinks:
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512072 1 20 24 28676032
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After 4 blinks:
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512 72 2024 2 0 2 4 2867 6032
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After 5 blinks:
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1036288 7 2 20 24 4048 1 4048 8096 28 67 60 32
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After 6 blinks:
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2097446912 14168 4048 2 0 2 4 40 48 2024 40 48 80 96 2 8 6 7 6 0 3 2
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In this example, after blinking six times, you would have 22 stones. After
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blinking 25 times, you would have 55312 stones!
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Consider the arrangement of stones in front of you. How many stones will
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you have after blinking 25 times?
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Your puzzle answer was 231278.
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--- Part Two ---
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The Historians sure are taking a long time. To be fair, the infinite
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corridors are very large.
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How many stones would you have after blinking a total of 75 times?
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Your puzzle answer was 274229228071551.
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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 [17]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 [18]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/2019/day/20
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17. https://adventofcode.com/2024
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18. https://adventofcode.com/2024/day/11/input
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