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Advent of Code
--- Day 21: Keypad Conundrum ---
As you teleport onto Santa's [16]Reindeer-class starship, The Historians
begin to panic: someone from their search party is missing. A quick
life-form scan by the ship's computer reveals that when the missing
Historian teleported, he arrived in another part of the ship.
The door to that area is locked, but the computer can't open it; it can
only be opened by physically typing the door codes (your puzzle input) on
the numeric keypad on the door.
The numeric keypad has four rows of buttons: 789, 456, 123, and finally an
empty gap followed by 0A. Visually, they are arranged like this:
+---+---+---+
| 7 | 8 | 9 |
+---+---+---+
| 4 | 5 | 6 |
+---+---+---+
| 1 | 2 | 3 |
+---+---+---+
| 0 | A |
+---+---+
Unfortunately, the area outside the door is currently depressurized and
nobody can go near the door. A robot needs to be sent instead.
The robot has no problem navigating the ship and finding the numeric
keypad, but it's not designed for button pushing: it can't be told to push
a specific button directly. Instead, it has a robotic arm that can be
controlled remotely via a directional keypad.
The directional keypad has two rows of buttons: a gap / ^ (up) / A
(activate) on the first row and < (left) / v (down) / > (right) on the
second row. Visually, they are arranged like this:
+---+---+
| ^ | A |
+---+---+---+
| < | v | > |
+---+---+---+
When the robot arrives at the numeric keypad, its robotic arm is pointed
at the A button in the bottom right corner. After that, this directional
keypad remote control must be used to maneuver the robotic arm: the up /
down / left / right buttons cause it to move its arm one button in that
direction, and the A button causes the robot to briefly move forward,
pressing the button being aimed at by the robotic arm.
For example, to make the robot type 029A on the numeric keypad, one
sequence of inputs on the directional keypad you could use is:
• < to move the arm from A (its initial position) to 0.
• A to push the 0 button.
• ^A to move the arm to the 2 button and push it.
• >^^A to move the arm to the 9 button and push it.
• vvvA to move the arm to the A button and push it.
In total, there are three shortest possible sequences of button presses on
this directional keypad that would cause the robot to type 029A:
<A^A>^^AvvvA, <A^A^>^AvvvA, and <A^A^^>AvvvA.
Unfortunately, the area containing this directional keypad remote control
is currently experiencing high levels of radiation and nobody can go near
it. A robot needs to be sent instead.
When the robot arrives at the directional keypad, its robot arm is pointed
at the A button in the upper right corner. After that, a second, different
directional keypad remote control is used to control this robot (in the
same way as the first robot, except that this one is typing on a
directional keypad instead of a numeric keypad).
There are multiple shortest possible sequences of directional keypad
button presses that would cause this robot to tell the first robot to type
029A on the door. One such sequence is v<<A>>^A<A>AvA<^AA>A<vAAA>^A.
Unfortunately, the area containing this second directional keypad remote
control is currently -40 degrees! Another robot will need to be sent to
type on that directional keypad, too.
There are many shortest possible sequences of directional keypad button
presses that would cause this robot to tell the second robot to tell the
first robot to eventually type 029A on the door. One such sequence is
<vA<AA>>^AvAA<^A>A<v<A>>^AvA^A<vA>^A<v<A>^A>AAvA^A<v<A>A>^AAAvA<^A>A.
Unfortunately, the area containing this third directional keypad remote
control is currently full of Historians, so no robots can find a clear
path there. Instead, you will have to type this sequence yourself.
Were you to choose this sequence of button presses, here are all of the
buttons that would be pressed on your directional keypad, the two robots'
directional keypads, and the numeric keypad:
<vA<AA>>^AvAA<^A>A<v<A>>^AvA^A<vA>^A<v<A>^A>AAvA^A<v<A>A>^AAAvA<^A>A
v<<A>>^A<A>AvA<^AA>A<vAAA>^A
<A^A>^^AvvvA
029A
In summary, there are the following keypads:
• One directional keypad that you are using.
• Two directional keypads that robots are using.
• One numeric keypad (on a door) that a robot is using.
It is important to remember that these robots are not designed for button
pushing. In particular, if a robot arm is ever aimed at a gap where no
button is present on the keypad, even for an instant, the robot will panic
unrecoverably. So, don't do that. All robots will initially aim at the
keypad's A key, wherever it is.
To unlock the door, five codes will need to be typed on its numeric
keypad. For example:
029A
980A
179A
456A
379A
For each of these, here is a shortest sequence of button presses you could
type to cause the desired code to be typed on the numeric keypad:
029A: <vA<AA>>^AvAA<^A>A<v<A>>^AvA^A<vA>^A<v<A>^A>AAvA^A<v<A>A>^AAAvA<^A>A
980A: <v<A>>^AAAvA^A<vA<AA>>^AvAA<^A>A<v<A>A>^AAAvA<^A>A<vA>^A<A>A
179A: <v<A>>^A<vA<A>>^AAvAA<^A>A<v<A>>^AAvA^A<vA>^AA<A>A<v<A>A>^AAAvA<^A>A
456A: <v<A>>^AA<vA<A>>^AAvAA<^A>A<vA>^A<A>A<vA>^A<A>A<v<A>A>^AAvA<^A>A
379A: <v<A>>^AvA^A<vA<AA>>^AAvA<^A>AAvA^A<vA>^AA<A>A<v<A>A>^AAAvA<^A>A
The Historians are getting nervous; the ship computer doesn't remember
whether the missing Historian is trapped in the area containing a giant
electromagnet or molten lava. You'll need to make sure that for each of
the five codes, you find the shortest sequence of button presses
necessary.
The complexity of a single code (like 029A) is equal to the result of
multiplying these two values:
• The length of the shortest sequence of button presses you need to type
on your directional keypad in order to cause the code to be typed on
the numeric keypad; for 029A, this would be 68.
• The numeric part of the code (ignoring leading zeroes); for 029A, this
would be 29.
In the above example, complexity of the five codes can be found by
calculating 68 * 29, 60 * 980, 68 * 179, 64 * 456, and 64 * 379. Adding
these together produces 126384.
Find the fewest number of button presses you'll need to perform in order
to cause the robot in front of the door to type each code. What is the sum
of the complexities of the five codes on your list?
Your puzzle answer was 248684.
--- Part Two ---
Just as the missing Historian is released, The Historians realize that a
second member of their search party has also been missing this entire
time!
A quick life-form scan reveals the Historian is also trapped in a locked
area of the ship. Due to a variety of hazards, robots are once again
dispatched, forming another chain of remote control keypads managing
robotic-arm-wielding robots.
This time, many more robots are involved. In summary, there are the
following keypads:
• One directional keypad that you are using.
• 25 directional keypads that robots are using.
• One numeric keypad (on a door) that a robot is using.
The keypads form a chain, just like before: your directional keypad
controls a robot which is typing on a directional keypad which controls a
robot which is typing on a directional keypad... and so on, ending with
the robot which is typing on the numeric keypad.
The door codes are the same this time around; only the number of robots
and directional keypads has changed.
Find the fewest number of button presses you'll need to perform in order
to cause the robot in front of the door to type each code. What is the sum
of the complexities of the five codes on your list?
Your puzzle answer was 307055584161760.
Both parts of this puzzle are complete! They provide two gold stars: **
At this point, you should [17]return to your Advent calendar and try
another puzzle.
If you still want to see it, you can [18]get your puzzle input.
References
Visible links
1. https://adventofcode.com/
2. https://adventofcode.com/2024/about
3. https://adventofcode.com/2024/events
4. https://cottonbureau.com/people/advent-of-code
5. https://adventofcode.com/2024/settings
6. https://adventofcode.com/2024/auth/logout
7. Advent of Code Supporter
https://adventofcode.com/2024/support
8. https://adventofcode.com/2024
9. https://adventofcode.com/2024
10. https://adventofcode.com/2024/support
11. https://adventofcode.com/2024/sponsors
12. https://adventofcode.com/2024/leaderboard
13. https://adventofcode.com/2024/stats
14. https://adventofcode.com/2024/sponsors
16. https://adventofcode.com/2019/day/25
17. https://adventofcode.com/2024
18. https://adventofcode.com/2024/day/21/input

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Advent of Code
--- Day 22: Monkey Market ---
As you're all teleported deep into the jungle, a [16]monkey steals The
Historians' device! You'll need to get it back while The Historians are
looking for the Chief.
The monkey that stole the device seems willing to trade it, but only in
exchange for an absurd number of bananas. Your only option is to buy
bananas on the Monkey Exchange Market.
You aren't sure how the Monkey Exchange Market works, but one of The
Historians senses trouble and comes over to help. Apparently, they've been
studying these monkeys for a while and have deciphered their secrets.
Today, the Market is full of monkeys buying good hiding spots.
Fortunately, because of the time you recently spent in this jungle, you
know lots of good hiding spots you can sell! If you sell enough hiding
spots, you should be able to get enough bananas to buy the device back.
On the Market, the buyers seem to use random prices, but their prices are
actually only [17]pseudorandom! If you know the secret of how they pick
their prices, you can wait for the perfect time to sell.
The part about secrets is literal, the Historian explains. Each buyer
produces a pseudorandom sequence of secret numbers where each secret is
derived from the previous.
In particular, each buyer's secret number evolves into the next secret
number in the sequence via the following process:
• Calculate the result of multiplying the secret number by 64. Then, mix
this result into the secret number. Finally, prune the secret number.
• Calculate the result of dividing the secret number by 32. Round the
result down to the nearest integer. Then, mix this result into the
secret number. Finally, prune the secret number.
• Calculate the result of multiplying the secret number by 2048. Then,
mix this result into the secret number. Finally, prune the secret
number.
Each step of the above process involves mixing and pruning:
• To mix a value into the secret number, calculate the [18]bitwise XOR
of the given value and the secret number. Then, the secret number
becomes the result of that operation. (If the secret number is 42 and
you were to mix 15 into the secret number, the secret number would
become 37.)
• To prune the secret number, calculate the value of the secret number
[19]modulo 16777216. Then, the secret number becomes the result of
that operation. (If the secret number is 100000000 and you were to
prune the secret number, the secret number would become 16113920.)
After this process completes, the buyer is left with the next secret
number in the sequence. The buyer can repeat this process as many times as
necessary to produce more secret numbers.
So, if a buyer had a secret number of 123, that buyer's next ten secret
numbers would be:
15887950
16495136
527345
704524
1553684
12683156
11100544
12249484
7753432
5908254
Each buyer uses their own secret number when choosing their price, so it's
important to be able to predict the sequence of secret numbers for each
buyer. Fortunately, the Historian's research has uncovered the initial
secret number of each buyer (your puzzle input). For example:
1
10
100
2024
This list describes the initial secret number of four different
secret-hiding-spot-buyers on the Monkey Exchange Market. If you can
simulate secret numbers from each buyer, you'll be able to predict all of
their future prices.
In a single day, buyers each have time to generate 2000 new secret
numbers. In this example, for each buyer, their initial secret number and
the 2000th new secret number they would generate are:
1: 8685429
10: 4700978
100: 15273692
2024: 8667524
Adding up the 2000th new secret number for each buyer produces 37327623.
For each buyer, simulate the creation of 2000 new secret numbers. What is
the sum of the 2000th secret number generated by each buyer?
Your puzzle answer was 14082561342.
--- Part Two ---
Of course, the secret numbers aren't the prices each buyer is offering!
That would be ridiculous. Instead, the prices the buyer offers are just
the ones digit of each of their secret numbers.
So, if a buyer starts with a secret number of 123, that buyer's first ten
prices would be:
3 (from 123)
0 (from 15887950)
6 (from 16495136)
5 (etc.)
4
4
6
4
4
2
This price is the number of bananas that buyer is offering in exchange for
your information about a new hiding spot. However, you still don't speak
[20]monkey, so you can't negotiate with the buyers directly. The Historian
speaks a little, but not enough to negotiate; instead, he can ask another
monkey to negotiate on your behalf.
Unfortunately, the monkey only knows how to decide when to sell by looking
at the changes in price. Specifically, the monkey will only look for a
specific sequence of four consecutive changes in price, then immediately
sell when it sees that sequence.
So, if a buyer starts with a secret number of 123, that buyer's first ten
secret numbers, prices, and the associated changes would be:
123: 3
15887950: 0 (-3)
16495136: 6 (6)
527345: 5 (-1)
704524: 4 (-1)
1553684: 4 (0)
12683156: 6 (2)
11100544: 4 (-2)
12249484: 4 (0)
7753432: 2 (-2)
Note that the first price has no associated change because there was no
previous price to compare it with.
In this short example, within just these first few prices, the highest
price will be 6, so it would be nice to give the monkey instructions that
would make it sell at that time. The first 6 occurs after only two
changes, so there's no way to instruct the monkey to sell then, but the
second 6 occurs after the changes -1,-1,0,2. So, if you gave the monkey
that sequence of changes, it would wait until the first time it sees that
sequence and then immediately sell your hiding spot information at the
current price, winning you 6 bananas.
Each buyer only wants to buy one hiding spot, so after the hiding spot is
sold, the monkey will move on to the next buyer. If the monkey never hears
that sequence of price changes from a buyer, the monkey will never sell,
and will instead just move on to the next buyer.
Worse, you can only give the monkey a single sequence of four price
changes to look for. You can't change the sequence between buyers.
You're going to need as many bananas as possible, so you'll need to
determine which sequence of four price changes will cause the monkey to
get you the most bananas overall. Each buyer is going to generate 2000
secret numbers after their initial secret number, so, for each buyer,
you'll have 2000 price changes in which your sequence can occur.
Suppose the initial secret number of each buyer is:
1
2
3
2024
There are many sequences of four price changes you could tell the monkey,
but for these four buyers, the sequence that will get you the most bananas
is -2,1,-1,3. Using that sequence, the monkey will make the following
sales:
• For the buyer with an initial secret number of 1, changes -2,1,-1,3
first occur when the price is 7.
• For the buyer with initial secret 2, changes -2,1,-1,3 first occur
when the price is 7.
• For the buyer with initial secret 3, the change sequence -2,1,-1,3
does not occur in the first 2000 changes.
• For the buyer starting with 2024, changes -2,1,-1,3 first occur when
the price is 9.
So, by asking the monkey to sell the first time each buyer's prices go
down 2, then up 1, then down 1, then up 3, you would get 23 (7 + 7 + 9)
bananas!
Figure out the best sequence to tell the monkey so that by looking for
that same sequence of changes in every buyer's future prices, you get the
most bananas in total. What is the most bananas you can get?
Your puzzle answer was 1568.
Both parts of this puzzle are complete! They provide two gold stars: **
At this point, you should [21]return to your Advent calendar and try
another puzzle.
If you still want to see it, you can [22]get your puzzle input.
References
Visible links
1. https://adventofcode.com/
2. https://adventofcode.com/2024/about
3. https://adventofcode.com/2024/events
4. https://cottonbureau.com/people/advent-of-code
5. https://adventofcode.com/2024/settings
6. https://adventofcode.com/2024/auth/logout
7. Advent of Code Supporter
https://adventofcode.com/2024/support
8. https://adventofcode.com/2024
9. https://adventofcode.com/2024
10. https://adventofcode.com/2024/support
11. https://adventofcode.com/2024/sponsors
12. https://adventofcode.com/2024/leaderboard
13. https://adventofcode.com/2024/stats
14. https://adventofcode.com/2024/sponsors
16. https://adventofcode.com/2022/day/11
17. https://en.wikipedia.org/wiki/Pseudorandom_number_generator
18. https://en.wikipedia.org/wiki/Bitwise_operation#XOR
19. https://en.wikipedia.org/wiki/Modulo
20. https://adventofcode.com/2022/day/21
21. https://adventofcode.com/2024
22. https://adventofcode.com/2024/day/22/input

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[1]Advent of Code
--- Day 23: LAN Party ---
As The Historians wander around a secure area at Easter Bunny HQ, you come
across posters for a [16]LAN party scheduled for today! Maybe you can find
it; you connect to a nearby [17]datalink port and download a map of the
local network (your puzzle input).
The network map provides a list of every connection between two computers.
For example:
kh-tc
qp-kh
de-cg
ka-co
yn-aq
qp-ub
cg-tb
vc-aq
tb-ka
wh-tc
yn-cg
kh-ub
ta-co
de-co
tc-td
tb-wq
wh-td
ta-ka
td-qp
aq-cg
wq-ub
ub-vc
de-ta
wq-aq
wq-vc
wh-yn
ka-de
kh-ta
co-tc
wh-qp
tb-vc
td-yn
Each line of text in the network map represents a single connection; the
line kh-tc represents a connection between the computer named kh and the
computer named tc. Connections aren't directional; tc-kh would mean
exactly the same thing.
LAN parties typically involve multiplayer games, so maybe you can locate
it by finding groups of connected computers. Start by looking for sets of
three computers where each computer in the set is connected to the other
two computers.
In this example, there are 12 such sets of three inter-connected
computers:
aq,cg,yn
aq,vc,wq
co,de,ka
co,de,ta
co,ka,ta
de,ka,ta
kh,qp,ub
qp,td,wh
tb,vc,wq
tc,td,wh
td,wh,yn
ub,vc,wq
If the Chief Historian is here, and he's at the LAN party, it would be
best to know that right away. You're pretty sure his computer's name
starts with t, so consider only sets of three computers where at least one
computer's name starts with t. That narrows the list down to 7 sets of
three inter-connected computers:
co,de,ta
co,ka,ta
de,ka,ta
qp,td,wh
tb,vc,wq
tc,td,wh
td,wh,yn
Find all the sets of three inter-connected computers. How many contain at
least one computer with a name that starts with t?
Your puzzle answer was 1485.
--- Part Two ---
There are still way too many results to go through them all. You'll have
to find the LAN party another way and go there yourself.
Since it doesn't seem like any employees are around, you figure they must
all be at the LAN party. If that's true, the LAN party will be the largest
set of computers that are all connected to each other. That is, for each
computer at the LAN party, that computer will have a connection to every
other computer at the LAN party.
In the above example, the largest set of computers that are all connected
to each other is made up of co, de, ka, and ta. Each computer in this set
has a connection to every other computer in the set:
ka-co
ta-co
de-co
ta-ka
de-ta
ka-de
The LAN party posters say that the password to get into the LAN party is
the name of every computer at the LAN party, sorted alphabetically, then
joined together with commas. (The people running the LAN party are clearly
a bunch of nerds.) In this example, the password would be co,de,ka,ta.
What is the password to get into the LAN party?
Your puzzle answer was cc,dz,ea,hj,if,it,kf,qo,sk,ug,ut,uv,wh.
Both parts of this puzzle are complete! They provide two gold stars: **
At this point, you should [18]return to your Advent calendar and try
another puzzle.
If you still want to see it, you can [19]get your puzzle input.
References
Visible links
1. https://adventofcode.com/
2. https://adventofcode.com/2024/about
3. https://adventofcode.com/2024/events
4. https://cottonbureau.com/people/advent-of-code
5. https://adventofcode.com/2024/settings
6. https://adventofcode.com/2024/auth/logout
7. Advent of Code Supporter
https://adventofcode.com/2024/support
8. https://adventofcode.com/2024
9. https://adventofcode.com/2024
10. https://adventofcode.com/2024/support
11. https://adventofcode.com/2024/sponsors
12. https://adventofcode.com/2024/leaderboard
13. https://adventofcode.com/2024/stats
14. https://adventofcode.com/2024/sponsors
16. https://en.wikipedia.org/wiki/LAN_party
17. https://adventofcode.com/2016/day/9
18. https://adventofcode.com/2024
19. https://adventofcode.com/2024/day/23/input