You cannot select more than 25 topics
Topics must start with a letter or number, can include dashes ('-') and can be up to 35 characters long.
132 lines
4.0 KiB
Markdown
132 lines
4.0 KiB
Markdown
https://adventofcode.com/2021/day/1
|
|
|
|
## \--- Day 1: Sonar Sweep ---
|
|
|
|
You're minding your own business on a ship at sea when the overboard alarm
|
|
goes off! You rush to see if you can help. Apparently, one of the Elves
|
|
tripped and accidentally sent the sleigh keys flying into the ocean!
|
|
|
|
Before you know it, you're inside a submarine the Elves keep ready for
|
|
situations like this. It's covered in Christmas lights (because of course it
|
|
is), and it even has an experimental antenna that should be able to track the
|
|
keys if you can boost its signal strength high enough; there's a little meter
|
|
that indicates the antenna's signal strength by displaying 0-50 _stars_.
|
|
|
|
Your instincts tell you that in order to save Christmas, you'll 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!
|
|
|
|
As the submarine drops below the surface of the ocean, it automatically
|
|
performs a sonar sweep of the nearby sea floor. On a small screen, the sonar
|
|
sweep report (your puzzle input) appears: each line is a measurement of the
|
|
sea floor depth as the sweep looks further and further away from the
|
|
submarine.
|
|
|
|
For example, suppose you had the following report:
|
|
|
|
[code]
|
|
|
|
199
|
|
200
|
|
208
|
|
210
|
|
200
|
|
207
|
|
240
|
|
269
|
|
260
|
|
263
|
|
|
|
[/code]
|
|
|
|
This report indicates that, scanning outward from the submarine, the sonar
|
|
sweep found depths of `199`, `200`, `208`, `210`, and so on.
|
|
|
|
The first order of business is to figure out how quickly the depth increases,
|
|
just so you know what you're dealing with - you never know if the keys will
|
|
get carried into deeper water by an ocean current or a fish or something.
|
|
|
|
To do this, count _the number of times a depth measurement increases_ from the
|
|
previous measurement. (There is no measurement before the first measurement.)
|
|
In the example above, the changes are as follows:
|
|
|
|
[code]
|
|
|
|
199 (N/A - no previous measurement)
|
|
200 ( _increased_ )
|
|
208 ( _increased_ )
|
|
210 ( _increased_ )
|
|
200 (decreased)
|
|
207 ( _increased_ )
|
|
240 ( _increased_ )
|
|
269 ( _increased_ )
|
|
260 (decreased)
|
|
263 ( _increased_ )
|
|
|
|
[/code]
|
|
|
|
In this example, there are _`7`_ measurements that are larger than the
|
|
previous measurement.
|
|
|
|
_How many measurements are larger than the previous measurement?_
|
|
|
|
Your puzzle answer was `1754`.
|
|
|
|
## \--- Part Two ---
|
|
|
|
Considering every single measurement isn't as useful as you expected: there's
|
|
just too much noise in the data.
|
|
|
|
Instead, consider sums of a _three-measurement sliding window_. Again
|
|
considering the above example:
|
|
|
|
[code]
|
|
|
|
199 A
|
|
200 A B
|
|
208 A B C
|
|
210 B C D
|
|
200 E C D
|
|
207 E F D
|
|
240 E F G
|
|
269 F G H
|
|
260 G H
|
|
263 H
|
|
|
|
[/code]
|
|
|
|
Start by comparing the first and second three-measurement windows. The
|
|
measurements in the first window are marked `A` (`199`, `200`, `208`); their
|
|
sum is `199 + 200 + 208 = 607`. The second window is marked `B` (`200`, `208`,
|
|
`210`); its sum is `618`. The sum of measurements in the second window is
|
|
larger than the sum of the first, so this first comparison _increased_.
|
|
|
|
Your goal now is to count _the number of times the sum of measurements in this
|
|
sliding window increases_ from the previous sum. So, compare `A` with `B`,
|
|
then compare `B` with `C`, then `C` with `D`, and so on. Stop when there
|
|
aren't enough measurements left to create a new three-measurement sum.
|
|
|
|
In the above example, the sum of each three-measurement window is as follows:
|
|
|
|
[code]
|
|
|
|
A: 607 (N/A - no previous sum)
|
|
B: 618 ( _increased_ )
|
|
C: 618 (no change)
|
|
D: 617 (decreased)
|
|
E: 647 ( _increased_ )
|
|
F: 716 ( _increased_ )
|
|
G: 769 ( _increased_ )
|
|
H: 792 ( _increased_ )
|
|
|
|
[/code]
|
|
|
|
In this example, there are _`5`_ sums that are larger than the previous sum.
|
|
|
|
Consider sums of a three-measurement sliding window. _How many sums are larger
|
|
than the previous sum?_
|
|
|