103 lines
3.5 KiB
Markdown
103 lines
3.5 KiB
Markdown
## \-\-- Day 11: Plutonian Pebbles \-\--
|
|
|
|
The ancient civilization on [Pluto](/2019/day/20) was known for its
|
|
ability to manipulate spacetime, and while The Historians explore their
|
|
infinite corridors, you\'ve noticed a strange set of physics-defying
|
|
stones.
|
|
|
|
At first glance, they seem like normal stones: they\'re arranged in a
|
|
perfectly *straight line*, and each stone has a *number* engraved on it.
|
|
|
|
The strange part is that every time you
|
|
blink, the stones
|
|
*change*.
|
|
|
|
Sometimes, the number engraved on a stone changes. Other times, a stone
|
|
might *split in two*, causing all the other stones to shift over a bit
|
|
to make room in their perfectly straight line.
|
|
|
|
As you observe them for a while, you find that the stones have a
|
|
consistent behavior. Every time you blink, the stones each
|
|
*simultaneously* change according to the *first applicable rule* in this
|
|
list:
|
|
|
|
- If the stone is engraved with the number `0`, it is replaced by a
|
|
stone engraved with the number `1`.
|
|
- If the stone is engraved with a number that has an *even* number of
|
|
digits, it is replaced by *two stones*. The left half of the digits
|
|
are engraved on the new left stone, and the right half of the digits
|
|
are engraved on the new right stone. (The new numbers don\'t keep
|
|
extra leading zeroes: `1000` would become stones `10` and `0`.)
|
|
- If none of the other rules apply, the stone is replaced by a new
|
|
stone; the old stone\'s number *multiplied by 2024* is engraved on
|
|
the new stone.
|
|
|
|
No matter how the stones change, their *order is preserved*, and they
|
|
stay on their perfectly straight line.
|
|
|
|
How will the stones evolve if you keep blinking at them? You take a note
|
|
of the number engraved on each stone in the line (your puzzle input).
|
|
|
|
If you have an arrangement of five stones engraved with the numbers
|
|
`0 1 10 99 999` and you blink once, the stones transform as follows:
|
|
|
|
- The first stone, `0`, becomes a stone marked `1`.
|
|
- The second stone, `1`, is multiplied by 2024 to become `2024`.
|
|
- The third stone, `10`, is split into a stone marked `1` followed by
|
|
a stone marked `0`.
|
|
- The fourth stone, `99`, is split into two stones marked `9`.
|
|
- The fifth stone, `999`, is replaced by a stone marked `2021976`.
|
|
|
|
So, after blinking once, your five stones would become an arrangement of
|
|
seven stones engraved with the numbers `1 2024 1 0 9 9 2021976`.
|
|
|
|
Here is a longer example:
|
|
|
|
Initial arrangement:
|
|
125 17
|
|
|
|
After 1 blink:
|
|
253000 1 7
|
|
|
|
After 2 blinks:
|
|
253 0 2024 14168
|
|
|
|
After 3 blinks:
|
|
512072 1 20 24 28676032
|
|
|
|
After 4 blinks:
|
|
512 72 2024 2 0 2 4 2867 6032
|
|
|
|
After 5 blinks:
|
|
1036288 7 2 20 24 4048 1 4048 8096 28 67 60 32
|
|
|
|
After 6 blinks:
|
|
2097446912 14168 4048 2 0 2 4 40 48 2024 40 48 80 96 2 8 6 7 6 0 3 2
|
|
|
|
In this example, after blinking six times, you would have `22` stones.
|
|
After blinking 25 times, you would have `55312` stones!
|
|
|
|
Consider the arrangement of stones in front of you. *How many stones
|
|
will you have after blinking 25 times?*
|
|
|
|
Your puzzle answer was `211306`.
|
|
|
|
## \-\-- Part Two \-\-- {#part2}
|
|
|
|
The Historians sure are taking a long time. To be fair, the infinite
|
|
corridors *are* very large.
|
|
|
|
*How many stones would you have after blinking a total of 75 times?*
|
|
|
|
Your puzzle answer was `250783680217283`.
|
|
|
|
Both parts of this puzzle are complete! They provide two gold stars:
|
|
\*\*
|
|
|
|
At this point, you should [return to your Advent calendar](/2024) and
|
|
try another puzzle.
|
|
|
|
If you still want to see it, you can [get your puzzle
|
|
input](11/input).
|
|
|