101 lines
4.1 KiB
Markdown
101 lines
4.1 KiB
Markdown
|
## \-\-- Day 1: Chronal Calibration \-\--
|
|||
|
|
|
|||
|
|
\"We\'ve detected some temporal anomalies,\" one of Santa\'s Elves at
|
|||
|
|
the [Temporal Anomaly Research and Detection Instrument
|
|||
|
|
Station]{title="It's about as big on the inside as you expected."} tells
|
|||
|
|
you. She sounded pretty worried when she called you down here. \"At
|
|||
|
|
500-year intervals into the past, someone has been changing Santa\'s
|
|||
|
|
history!\"
|
|||
|
|
|
|||
|
|
\"The good news is that the changes won\'t propagate to our time stream
|
|||
|
|
for another 25 days, and we have a device\" - she attaches something to
|
|||
|
|
your wrist - \"that will let you fix the changes with no such
|
|||
|
|
propagation delay. It\'s configured to send you 500 years further into
|
|||
|
|
the past every few days; that was the best we could do on such short
|
|||
|
|
notice.\"
|
|||
|
|
|
|||
|
|
\"The bad news is that we are detecting roughly *fifty* anomalies
|
|||
|
|
throughout time; the device will indicate fixed anomalies with *stars*.
|
|||
|
|
The other bad news is that we only have one device and you\'re the best
|
|||
|
|
person for the job! Good lu\--\" She taps a button on the device and you
|
|||
|
|
suddenly feel like you\'re falling. To save Christmas, you need to get
|
|||
|
|
all *fifty stars* by December 25th.
|
|||
|
|
|
|||
|
|
Collect stars by solving puzzles. Two puzzles will be made available on
|
|||
|
|
each day in the Advent calendar; the second puzzle is unlocked when you
|
|||
|
|
complete the first. Each puzzle grants *one star*. Good luck!
|
|||
|
|
|
|||
|
|
After feeling like you\'ve been falling for a few minutes, you look at
|
|||
|
|
the device\'s tiny screen. \"Error: Device must be calibrated before
|
|||
|
|
first use. Frequency drift detected. Cannot maintain destination lock.\"
|
|||
|
|
Below the message, the device shows a sequence of changes in frequency
|
|||
|
|
(your puzzle input). A value like `+6` means the current frequency
|
|||
|
|
increases by `6`; a value like `-3` means the current frequency
|
|||
|
|
decreases by `3`.
|
|||
|
|
|
|||
|
|
For example, if the device displays frequency changes of
|
|||
|
|
`+1, -2, +3, +1`, then starting from a frequency of zero, the following
|
|||
|
|
changes would occur:
|
|||
|
|
|
|||
|
|
- Current frequency ` 0`, change of `+1`; resulting frequency ` 1`.
|
|||
|
|
- Current frequency ` 1`, change of `-2`; resulting frequency `-1`.
|
|||
|
|
- Current frequency `-1`, change of `+3`; resulting frequency ` 2`.
|
|||
|
|
- Current frequency ` 2`, change of `+1`; resulting frequency ` 3`.
|
|||
|
|
|
|||
|
|
In this example, the resulting frequency is `3`.
|
|||
|
|
|
|||
|
|
Here are other example situations:
|
|||
|
|
|
|||
|
|
- `+1, +1, +1` results in ` 3`
|
|||
|
|
- `+1, +1, -2` results in ` 0`
|
|||
|
|
- `-1, -2, -3` results in `-6`
|
|||
|
|
|
|||
|
|
Starting with a frequency of zero, *what is the resulting frequency*
|
|||
|
|
after all of the changes in frequency have been applied?
|
|||
|
|
|
|||
|
|
Your puzzle answer was `474`.
|
|||
|
|
|
|||
|
|
## \-\-- Part Two \-\-- {#part2}
|
|||
|
|
|
|||
|
|
You notice that the device repeats the same frequency change list over
|
|||
|
|
and over. To calibrate the device, you need to find the first frequency
|
|||
|
|
it reaches *twice*.
|
|||
|
|
|
|||
|
|
For example, using the same list of changes above, the device would loop
|
|||
|
|
as follows:
|
|||
|
|
|
|||
|
|
- Current frequency ` 0`, change of `+1`; resulting frequency ` 1`.
|
|||
|
|
- Current frequency ` 1`, change of `-2`; resulting frequency `-1`.
|
|||
|
|
- Current frequency `-1`, change of `+3`; resulting frequency ` 2`.
|
|||
|
|
- Current frequency ` 2`, change of `+1`; resulting frequency ` 3`.
|
|||
|
|
- (At this point, the device continues from the start of the list.)
|
|||
|
|
- Current frequency ` 3`, change of `+1`; resulting frequency ` 4`.
|
|||
|
|
- Current frequency ` 4`, change of `-2`; resulting frequency ` 2`,
|
|||
|
|
which has already been seen.
|
|||
|
|
|
|||
|
|
In this example, the first frequency reached twice is `2`. Note that
|
|||
|
|
your device might need to repeat its list of frequency changes many
|
|||
|
|
times before a duplicate frequency is found, and that duplicates might
|
|||
|
|
be found while in the middle of processing the list.
|
|||
|
|
|
|||
|
|
Here are other examples:
|
|||
|
|
|
|||
|
|
- `+1, -1` first reaches `0` twice.
|
|||
|
|
- `+3, +3, +4, -2, -4` first reaches `10` twice.
|
|||
|
|
- `-6, +3, +8, +5, -6` first reaches `5` twice.
|
|||
|
|
- `+7, +7, -2, -7, -4` first reaches `14` twice.
|
|||
|
|
|
|||
|
|
*What is the first frequency your device reaches twice?*
|
|||
|
|
|
|||
|
|
Your puzzle answer was `137041`.
|
|||
|
|
|
|||
|
|
Both parts of this puzzle are complete! They provide two gold stars:
|
|||
|
|
\*\*
|
|||
|
|
|
|||
|
|
At this point, you should [return to your Advent calendar](/2018) and
|
|||
|
|
try another puzzle.
|
|||
|
|
|
|||
|
|
If you still want to see it, you can [get your puzzle
|
|||
|
|
input](1/input).
|
|||
|
|
|