47 lines
2.1 KiB
Text
47 lines
2.1 KiB
Text
|
\--- Day 16: Permutation Promenade ---
|
||
|
|
----------
|
||
|
|
|
||
|
|
You come upon a very unusual sight; a group of programs here appear to be [dancing](https://www.youtube.com/watch?v=lyZQPjUT5B4&t=53).
|
||
|
|
|
||
|
|
There are sixteen programs in total, named `a` through `p`. They start by standing in a line: `a` stands in position `0`, `b` stands in position `1`, and so on until `p`, which stands in position `15`.
|
||
|
|
|
||
|
|
The programs' *dance* consists of a sequence of *dance moves*:
|
||
|
|
|
||
|
|
* *Spin*, written `sX`, makes `X` programs move from the end to the front, but maintain their order otherwise. (For example, `s3` on `abcde` produces `cdeab`).
|
||
|
|
* *Exchange*, written `xA/B`, makes the programs at positions `A` and `B` swap places.
|
||
|
|
* *Partner*, written `pA/B`, makes the programs named `A` and `B` swap places.
|
||
|
|
|
||
|
|
For example, with only five programs standing in a line (`abcde`), they could do the following dance:
|
||
|
|
|
||
|
|
* `s1`, a spin of size `1`: `eabcd`.
|
||
|
|
* `x3/4`, swapping the last two programs: `eabdc`.
|
||
|
|
* `pe/b`, swapping programs `e` and `b`: `baedc`.
|
||
|
|
|
||
|
|
After finishing their dance, the programs end up in order `baedc`.
|
||
|
|
|
||
|
|
You watch the dance for a while and record their dance moves (your puzzle input). *In what order are the programs standing* after their dance?
|
||
|
|
|
||
|
|
Your puzzle answer was `cgpfhdnambekjiol`.
|
||
|
|
|
||
|
|
\--- Part Two ---
|
||
|
|
----------
|
||
|
|
|
||
|
|
Now that you're starting to get a feel for the dance moves, you turn your attention to *the dance as a whole*.
|
||
|
|
|
||
|
|
Keeping the positions they ended up in from their previous dance, the programs perform it again and again: including the first dance, a total of *one billion* (`1000000000`) times.
|
||
|
|
|
||
|
|
In the example above, their second dance would *begin* with the order `baedc`, and use the same dance moves:
|
||
|
|
|
||
|
|
* `s1`, a spin of size `1`: `cbaed`.
|
||
|
|
* `x3/4`, swapping the last two programs: `cbade`.
|
||
|
|
* `pe/b`, swapping programs `e` and `b`: `ceadb`.
|
||
|
|
|
||
|
|
*In what order are the programs standing* after their billion dances?
|
||
|
|
|
||
|
|
Your puzzle answer was `gjmiofcnaehpdlbk`.
|
||
|
|
|
||
|
|
Both parts of this puzzle are complete! They provide two gold stars: \*\*
|
||
|
|
|
||
|
|
At this point, all that is left is for you to [admire your Advent calendar](/2017).
|
||
|
|
|
||
|
|
If you still want to see it, you can [get your puzzle input](16/input).
|