182 lines
5.1 KiB
Markdown
182 lines
5.1 KiB
Markdown
## \-\-- Day 14: Restroom Redoubt \-\--
|
|
|
|
One of The Historians needs to use the bathroom; fortunately, you know
|
|
there\'s a bathroom near an unvisited location on their list, and so
|
|
you\'re all quickly teleported directly to the lobby of Easter Bunny
|
|
Headquarters.
|
|
|
|
Unfortunately, EBHQ seems to have \"improved\" bathroom security *again*
|
|
after your last [visit](/2016/day/2). The area outside the bathroom is
|
|
swarming with robots!
|
|
|
|
To get The Historian safely to the bathroom, you\'ll need a way to
|
|
predict where the robots will be in the future. Fortunately, they all
|
|
seem to be moving on the tile floor in predictable *straight lines*.
|
|
|
|
You make a list (your puzzle input) of all of the robots\' current
|
|
*positions* (`p`) and *velocities* (`v`), one robot per line. For
|
|
example:
|
|
|
|
p=0,4 v=3,-3
|
|
p=6,3 v=-1,-3
|
|
p=10,3 v=-1,2
|
|
p=2,0 v=2,-1
|
|
p=0,0 v=1,3
|
|
p=3,0 v=-2,-2
|
|
p=7,6 v=-1,-3
|
|
p=3,0 v=-1,-2
|
|
p=9,3 v=2,3
|
|
p=7,3 v=-1,2
|
|
p=2,4 v=2,-3
|
|
p=9,5 v=-3,-3
|
|
|
|
Each robot\'s position is given as `p=x,y` where `x` represents the
|
|
number of tiles the robot is from the left wall and `y` represents the
|
|
number of tiles from the top wall (when viewed from above). So, a
|
|
position of `p=0,0` means the robot is all the way in the top-left
|
|
corner.
|
|
|
|
Each robot\'s velocity is given as `v=x,y` where `x` and `y` are given
|
|
in *tiles per second*. Positive `x` means the robot is moving to the
|
|
*right*, and positive `y` means the robot is moving *down*. So, a
|
|
velocity of `v=1,-2` means that each second, the robot moves `1` tile to
|
|
the right and `2` tiles up.
|
|
|
|
The robots outside the actual bathroom are in a space which is `101`
|
|
tiles wide and `103` tiles tall (when viewed from above). However, in
|
|
this example, the robots are in a space which is only `11` tiles wide
|
|
and `7` tiles tall.
|
|
|
|
The robots are good at navigating over/under each other (due to a
|
|
combination of springs, extendable legs, and quadcopters), so they can
|
|
share the same tile and don\'t interact with each other. Visually, the
|
|
number of robots on each tile in this example looks like this:
|
|
|
|
1.12.......
|
|
...........
|
|
...........
|
|
......11.11
|
|
1.1........
|
|
.........1.
|
|
.......1...
|
|
|
|
These robots have a unique feature for maximum bathroom security: they
|
|
can *teleport*. When a robot would run into an edge of the space
|
|
they\'re in, they instead *teleport to the other side*, effectively
|
|
wrapping around the edges. Here is what robot `p=2,4 v=2,-3` does for
|
|
the first few seconds:
|
|
|
|
Initial state:
|
|
...........
|
|
...........
|
|
...........
|
|
...........
|
|
..1........
|
|
...........
|
|
...........
|
|
|
|
After 1 second:
|
|
...........
|
|
....1......
|
|
...........
|
|
...........
|
|
...........
|
|
...........
|
|
...........
|
|
|
|
After 2 seconds:
|
|
...........
|
|
...........
|
|
...........
|
|
...........
|
|
...........
|
|
......1....
|
|
...........
|
|
|
|
After 3 seconds:
|
|
...........
|
|
...........
|
|
........1..
|
|
...........
|
|
...........
|
|
...........
|
|
...........
|
|
|
|
After 4 seconds:
|
|
...........
|
|
...........
|
|
...........
|
|
...........
|
|
...........
|
|
...........
|
|
..........1
|
|
|
|
After 5 seconds:
|
|
...........
|
|
...........
|
|
...........
|
|
.1.........
|
|
...........
|
|
...........
|
|
...........
|
|
|
|
The Historian can\'t wait much longer, so you don\'t have to simulate
|
|
the robots for very long. Where will the robots be after `100` seconds?
|
|
|
|
In the above example, the number of robots on each tile after 100
|
|
seconds has elapsed looks like this:
|
|
|
|
......2..1.
|
|
...........
|
|
1..........
|
|
.11........
|
|
.....1.....
|
|
...12......
|
|
.1....1....
|
|
|
|
To determine the safest area, count the *number of robots in each
|
|
quadrant* after 100 seconds. Robots that are exactly in the middle
|
|
(horizontally or vertically) don\'t count as being in any quadrant, so
|
|
the only relevant robots are:
|
|
|
|
..... 2..1.
|
|
..... .....
|
|
1.... .....
|
|
|
|
..... .....
|
|
...12 .....
|
|
.1... 1....
|
|
|
|
In this example, the quadrants contain `1`, `3`, `4`, and `1` robot.
|
|
Multiplying these together gives a total *safety factor* of `12`.
|
|
|
|
Predict the motion of the robots in your list within a space which is
|
|
`101` tiles wide and `103` tiles tall. *What will the safety factor be
|
|
after exactly 100 seconds have elapsed?*
|
|
|
|
Your puzzle answer was `230686500`.
|
|
|
|
## \-\-- Part Two \-\-- {#part2}
|
|
|
|
During the bathroom break, someone notices that these robots seem
|
|
awfully similar to ones built and used at the North Pole. If they\'re
|
|
the same type of robots, they should have a hard-coded [Easter
|
|
egg]{title="This puzzle was originally going to be about the motion of space rocks in a fictitious arcade game called Meteoroids, but we just had an arcade puzzle."}:
|
|
very rarely, most of the robots should arrange themselves into *a
|
|
picture of a Christmas tree*.
|
|
|
|
*What is the fewest number of seconds that must elapse for the robots to
|
|
display the Easter egg?*
|
|
|
|
Your puzzle answer was `7672`.
|
|
|
|
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](14/input).
|
|
|