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Advent of Code
--- Day 13: Care Package ---
As you ponder the solitude of space and the ever-increasing three-hour roundtrip for messages between you and Earth, you
notice that the Space Mail Indicator Light is blinking. To help keep you sane, the Elves have sent you a care package.
It's a new game for the ship's arcade cabinet! Unfortunately, the arcade is all the way on the other end of the ship. Surely,
it won't be hard to build your own - the care package even comes with schematics.
The arcade cabinet runs Intcode software like the game the Elves sent (your puzzle input). It has a primitive screen capable
of drawing square tiles on a grid. The software draws tiles to the screen with output instructions: every three output
instructions specify the x position (distance from the left), y position (distance from the top), and tile id. The tile id is
interpreted as follows:
• 0 is an empty tile. No game object appears in this tile.
• 1 is a wall tile. Walls are indestructible barriers.
• 2 is a block tile. Blocks can be broken by the ball.
• 3 is a horizontal paddle tile. The paddle is indestructible.
• 4 is a ball tile. The ball moves diagonally and bounces off objects.
For example, a sequence of output values like 1,2,3,6,5,4 would draw a horizontal paddle tile (1 tile from the left and 2
tiles from the top) and a ball tile (6 tiles from the left and 5 tiles from the top).
Start the game. How many block tiles are on the screen when the game exits?
Your puzzle answer was 284.
--- Part Two ---
The game didn't run because you didn't put in any quarters. Unfortunately, you did not bring any quarters. Memory address 0
represents the number of quarters that have been inserted; set it to 2 to play for free.
The arcade cabinet has a joystick that can move left and right. The software reads the position of the joystick with input
instructions:
• If the joystick is in the neutral position, provide 0.
• If the joystick is tilted to the left, provide -1.
• If the joystick is tilted to the right, provide 1.
The arcade cabinet also has a segment display capable of showing a single number that represents the player's current score.
When three output instructions specify X=-1, Y=0, the third output instruction is not a tile; the value instead specifies the
new score to show in the segment display. For example, a sequence of output values like -1,0,12345 would show 12345 as the
player's current score.
Beat the game by breaking all the blocks. What is your score after the last block is broken?
Your puzzle answer was 13581.
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.
If you still want to see it, you can get your puzzle input.
References
Visible links
. https://adventofcode.com/
. https://adventofcode.com/2019/about
. https://adventofcode.com/2019/events
. https://adventofcode.com/2019/settings
. https://adventofcode.com/2019/auth/logout
. Advent of Code Supporter
https://adventofcode.com/2019/support
. https://adventofcode.com/2019
. https://adventofcode.com/2019
. https://adventofcode.com/2019/support
. https://adventofcode.com/2019/sponsors
. https://adventofcode.com/2019/leaderboard
. https://adventofcode.com/2019/stats
. https://adventofcode.com/2019/sponsors
. https://en.wikipedia.org/wiki/Arcade_cabinet
. https://adventofcode.com/2019/day/9
. https://en.wikipedia.org/wiki/Joystick
. https://en.wikipedia.org/wiki/Display_device#Segment_displays
. https://adventofcode.com/2019
. https://adventofcode.com/2019/day/13/input

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Advent of Code
--- Day 14: Space Stoichiometry ---
As you approach the rings of Saturn, your ship's low fuel indicator turns on. There isn't any fuel here, but the rings have
plenty of raw material. Perhaps your ship's Inter-Stellar Refinery Union brand nanofactory can turn these raw materials into
fuel.
You ask the nanofactory to produce a list of the reactions it can perform that are relevant to this process (your puzzle
input). Every reaction turns some quantities of specific input chemicals into some quantity of an output chemical. Almost
every chemical is produced by exactly one reaction; the only exception, ORE, is the raw material input to the entire process
and is not produced by a reaction.
You just need to know how much ORE you'll need to collect before you can produce one unit of FUEL.
Each reaction gives specific quantities for its inputs and output; reactions cannot be partially run, so only whole integer
multiples of these quantities can be used. (It's okay to have leftover chemicals when you're done, though.) For example, the
reaction 1 A, 2 B, 3 C => 2 D means that exactly 2 units of chemical D can be produced by consuming exactly 1 A, 2 B and 3 C.
You can run the full reaction as many times as necessary; for example, you could produce 10 D by consuming 5 A, 10 B, and 15
C.
Suppose your nanofactory produces the following list of reactions:
10 ORE => 10 A
1 ORE => 1 B
7 A, 1 B => 1 C
7 A, 1 C => 1 D
7 A, 1 D => 1 E
7 A, 1 E => 1 FUEL
The first two reactions use only ORE as inputs; they indicate that you can produce as much of chemical A as you want (in
increments of 10 units, each 10 costing 10 ORE) and as much of chemical B as you want (each costing 1 ORE). To produce 1
FUEL, a total of 31 ORE is required: 1 ORE to produce 1 B, then 30 more ORE to produce the 7 + 7 + 7 + 7 = 28 A (with 2 extra
A wasted) required in the reactions to convert the B into C, C into D, D into E, and finally E into FUEL. (30 A is produced
because its reaction requires that it is created in increments of 10.)
Or, suppose you have the following list of reactions:
9 ORE => 2 A
8 ORE => 3 B
7 ORE => 5 C
3 A, 4 B => 1 AB
5 B, 7 C => 1 BC
4 C, 1 A => 1 CA
2 AB, 3 BC, 4 CA => 1 FUEL
The above list of reactions requires 165 ORE to produce 1 FUEL:
• Consume 45 ORE to produce 10 A.
• Consume 64 ORE to produce 24 B.
• Consume 56 ORE to produce 40 C.
• Consume 6 A, 8 B to produce 2 AB.
• Consume 15 B, 21 C to produce 3 BC.
• Consume 16 C, 4 A to produce 4 CA.
• Consume 2 AB, 3 BC, 4 CA to produce 1 FUEL.
Here are some larger examples:
• 13312 ORE for 1 FUEL:
157 ORE => 5 NZVS
165 ORE => 6 DCFZ
44 XJWVT, 5 KHKGT, 1 QDVJ, 29 NZVS, 9 GPVTF, 48 HKGWZ => 1 FUEL
12 HKGWZ, 1 GPVTF, 8 PSHF => 9 QDVJ
179 ORE => 7 PSHF
177 ORE => 5 HKGWZ
7 DCFZ, 7 PSHF => 2 XJWVT
165 ORE => 2 GPVTF
3 DCFZ, 7 NZVS, 5 HKGWZ, 10 PSHF => 8 KHKGT
• 180697 ORE for 1 FUEL:
2 VPVL, 7 FWMGM, 2 CXFTF, 11 MNCFX => 1 STKFG
17 NVRVD, 3 JNWZP => 8 VPVL
53 STKFG, 6 MNCFX, 46 VJHF, 81 HVMC, 68 CXFTF, 25 GNMV => 1 FUEL
22 VJHF, 37 MNCFX => 5 FWMGM
139 ORE => 4 NVRVD
144 ORE => 7 JNWZP
5 MNCFX, 7 RFSQX, 2 FWMGM, 2 VPVL, 19 CXFTF => 3 HVMC
5 VJHF, 7 MNCFX, 9 VPVL, 37 CXFTF => 6 GNMV
145 ORE => 6 MNCFX
1 NVRVD => 8 CXFTF
1 VJHF, 6 MNCFX => 4 RFSQX
176 ORE => 6 VJHF
• 2210736 ORE for 1 FUEL:
171 ORE => 8 CNZTR
7 ZLQW, 3 BMBT, 9 XCVML, 26 XMNCP, 1 WPTQ, 2 MZWV, 1 RJRHP => 4 PLWSL
114 ORE => 4 BHXH
14 VRPVC => 6 BMBT
6 BHXH, 18 KTJDG, 12 WPTQ, 7 PLWSL, 31 FHTLT, 37 ZDVW => 1 FUEL
6 WPTQ, 2 BMBT, 8 ZLQW, 18 KTJDG, 1 XMNCP, 6 MZWV, 1 RJRHP => 6 FHTLT
15 XDBXC, 2 LTCX, 1 VRPVC => 6 ZLQW
13 WPTQ, 10 LTCX, 3 RJRHP, 14 XMNCP, 2 MZWV, 1 ZLQW => 1 ZDVW
5 BMBT => 4 WPTQ
189 ORE => 9 KTJDG
1 MZWV, 17 XDBXC, 3 XCVML => 2 XMNCP
12 VRPVC, 27 CNZTR => 2 XDBXC
15 KTJDG, 12 BHXH => 5 XCVML
3 BHXH, 2 VRPVC => 7 MZWV
121 ORE => 7 VRPVC
7 XCVML => 6 RJRHP
5 BHXH, 4 VRPVC => 5 LTCX
Given the list of reactions in your puzzle input, what is the minimum amount of ORE required to produce exactly 1 FUEL?
Your puzzle answer was 751038.
--- Part Two ---
After collecting ORE for a while, you check your cargo hold: 1 trillion (1000000000000) units of ORE.
With that much ore, given the examples above:
• The 13312 ORE-per-FUEL example could produce 82892753 FUEL.
• The 180697 ORE-per-FUEL example could produce 5586022 FUEL.
• The 2210736 ORE-per-FUEL example could produce 460664 FUEL.
Given 1 trillion ORE, what is the maximum amount of FUEL you can produce?
Your puzzle answer was 2074843.
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.
If you still want to see it, you can get your puzzle input.
References
Visible links
. https://adventofcode.com/
. https://adventofcode.com/2019/about
. https://adventofcode.com/2019/events
. https://adventofcode.com/2019/settings
. https://adventofcode.com/2019/auth/logout
. Advent of Code Supporter
https://adventofcode.com/2019/support
. https://adventofcode.com/2019
. https://adventofcode.com/2019
. https://adventofcode.com/2019/support
. https://adventofcode.com/2019/sponsors
. https://adventofcode.com/2019/leaderboard
. https://adventofcode.com/2019/stats
. https://adventofcode.com/2019/sponsors
. https://adventofcode.com/2019
. https://adventofcode.com/2019/day/14/input

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Advent of Code
--- Day 15: Oxygen System ---
Out here in deep space, many things can go wrong. Fortunately, many of those things have indicator lights. Unfortunately, one
of those lights is lit: the oxygen system for part of the ship has failed!
According to the readouts, the oxygen system must have failed days ago after a rupture in oxygen tank two; that section of
the ship was automatically sealed once oxygen levels went dangerously low. A single remotely-operated repair droid is your
only option for fixing the oxygen system.
The Elves' care package included an Intcode program (your puzzle input) that you can use to remotely control the repair
droid. By running that program, you can direct the repair droid to the oxygen system and fix the problem.
The remote control program executes the following steps in a loop forever:
• Accept a movement command via an input instruction.
• Send the movement command to the repair droid.
• Wait for the repair droid to finish the movement operation.
• Report on the status of the repair droid via an output instruction.
Only four movement commands are understood: north (1), south (2), west (3), and east (4). Any other command is invalid. The
movements differ in direction, but not in distance: in a long enough east-west hallway, a series of commands like
4,4,4,4,3,3,3,3 would leave the repair droid back where it started.
The repair droid can reply with any of the following status codes:
• 0: The repair droid hit a wall. Its position has not changed.
• 1: The repair droid has moved one step in the requested direction.
• 2: The repair droid has moved one step in the requested direction; its new position is the location of the oxygen system.
You don't know anything about the area around the repair droid, but you can figure it out by watching the status codes.
For example, we can draw the area using D for the droid, # for walls, . for locations the droid can traverse, and empty space
for unexplored locations. Then, the initial state looks like this:
D
To make the droid go north, send it 1. If it replies with 0, you know that location is a wall and that the droid didn't move:
#
D
To move east, send 4; a reply of 1 means the movement was successful:
#
.D
Then, perhaps attempts to move north (1), south (2), and east (4) are all met with replies of 0:
##
.D#
#
Now, you know the repair droid is in a dead end. Backtrack with 3 (which you already know will get a reply of 1 because you
already know that location is open):
##
D.#
#
Then, perhaps west (3) gets a reply of 0, south (2) gets a reply of 1, south again (2) gets a reply of 0, and then west (3)
gets a reply of 2:
##
#..#
D.#
#
Now, because of the reply of 2, you know you've found the oxygen system! In this example, it was only 2 moves away from the
repair droid's starting position.
What is the fewest number of movement commands required to move the repair droid from its starting position to the location
of the oxygen system?
Your puzzle answer was 240.
--- Part Two ---
You quickly repair the oxygen system; oxygen gradually fills the area.
Oxygen starts in the location containing the repaired oxygen system. It takes one minute for oxygen to spread to all open
locations that are adjacent to a location that already contains oxygen. Diagonal locations are not adjacent.
In the example above, suppose you've used the droid to explore the area fully and have the following map (where locations
that currently contain oxygen are marked O):
##
#..##
#.#..#
#.O.#
###
Initially, the only location which contains oxygen is the location of the repaired oxygen system. However, after one minute,
the oxygen spreads to all open (.) locations that are adjacent to a location containing oxygen:
##
#..##
#.#..#
#OOO#
###
After a total of two minutes, the map looks like this:
##
#..##
#O#O.#
#OOO#
###
After a total of three minutes:
##
#O.##
#O#OO#
#OOO#
###
And finally, the whole region is full of oxygen after a total of four minutes:
##
#OO##
#O#OO#
#OOO#
###
So, in this example, all locations contain oxygen after 4 minutes.
Use the repair droid to get a complete map of the area. How many minutes will it take to fill with oxygen?
Your puzzle answer was 322.
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.
If you still want to see it, you can get your puzzle input.
References
Visible links
. https://adventofcode.com/
. https://adventofcode.com/2019/about
. https://adventofcode.com/2019/events
. https://adventofcode.com/2019/settings
. https://adventofcode.com/2019/auth/logout
. Advent of Code Supporter
https://adventofcode.com/2019/support
. https://adventofcode.com/2019
. https://adventofcode.com/2019
. https://adventofcode.com/2019/support
. https://adventofcode.com/2019/sponsors
. https://adventofcode.com/2019/leaderboard
. https://adventofcode.com/2019/stats
. https://adventofcode.com/2019/sponsors
. https://adventofcode.com/2019/day/9
. https://adventofcode.com/2019
. https://adventofcode.com/2019/day/15/input

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Advent of Code
--- Day 16: Flawed Frequency Transmission ---
You're 3/4ths of the way through the gas giants. Not only do roundtrip signals to Earth take five hours, but the signal
quality is quite bad as well. You can clean up the signal with the Flawed Frequency Transmission algorithm, or FFT.
As input, FFT takes a list of numbers. In the signal you received (your puzzle input), each number is a single digit: data
like 15243 represents the sequence 1, 5, 2, 4, 3.
FFT operates in repeated phases. In each phase, a new list is constructed with the same length as the input list. This new
list is also used as the input for the next phase.
Each element in the new list is built by multiplying every value in the input list by a value in a repeating pattern and then
adding up the results. So, if the input list were 9, 8, 7, 6, 5 and the pattern for a given element were 1, 2, 3, the result
would be 9*1 + 8*2 + 7*3 + 6*1 + 5*2 (with each input element on the left and each value in the repeating pattern on the
right of each multiplication). Then, only the ones digit is kept: 38 becomes 8, -17 becomes 7, and so on.
While each element in the output array uses all of the same input array elements, the actual repeating pattern to use depends
on which output element is being calculated. The base pattern is 0, 1, 0, -1. Then, repeat each value in the pattern a number
of times equal to the position in the output list being considered. Repeat once for the first element, twice for the second
element, three times for the third element, and so on. So, if the third element of the output list is being calculated,
repeating the values would produce: 0, 0, 0, 1, 1, 1, 0, 0, 0, -1, -1, -1.
When applying the pattern, skip the very first value exactly once. (In other words, offset the whole pattern left by one.)
So, for the second element of the output list, the actual pattern used would be: 0, 1, 1, 0, 0, -1, -1, 0, 0, 1, 1, 0, 0, -1,
-1, ....
After using this process to calculate each element of the output list, the phase is complete, and the output list of this
phase is used as the new input list for the next phase, if any.
Given the input signal 12345678, below are four phases of FFT. Within each phase, each output digit is calculated on a single
line with the result at the far right; each multiplication operation shows the input digit on the left and the pattern value
on the right:
Input signal: 12345678
1*1 + 2*0 + 3*-1 + 4*0 + 5*1 + 6*0 + 7*-1 + 8*0 = 4
1*0 + 2*1 + 3*1 + 4*0 + 5*0 + 6*-1 + 7*-1 + 8*0 = 8
1*0 + 2*0 + 3*1 + 4*1 + 5*1 + 6*0 + 7*0 + 8*0 = 2
1*0 + 2*0 + 3*0 + 4*1 + 5*1 + 6*1 + 7*1 + 8*0 = 2
1*0 + 2*0 + 3*0 + 4*0 + 5*1 + 6*1 + 7*1 + 8*1 = 6
1*0 + 2*0 + 3*0 + 4*0 + 5*0 + 6*1 + 7*1 + 8*1 = 1
1*0 + 2*0 + 3*0 + 4*0 + 5*0 + 6*0 + 7*1 + 8*1 = 5
1*0 + 2*0 + 3*0 + 4*0 + 5*0 + 6*0 + 7*0 + 8*1 = 8
After 1 phase: 48226158
4*1 + 8*0 + 2*-1 + 2*0 + 6*1 + 1*0 + 5*-1 + 8*0 = 3
4*0 + 8*1 + 2*1 + 2*0 + 6*0 + 1*-1 + 5*-1 + 8*0 = 4
4*0 + 8*0 + 2*1 + 2*1 + 6*1 + 1*0 + 5*0 + 8*0 = 0
4*0 + 8*0 + 2*0 + 2*1 + 6*1 + 1*1 + 5*1 + 8*0 = 4
4*0 + 8*0 + 2*0 + 2*0 + 6*1 + 1*1 + 5*1 + 8*1 = 0
4*0 + 8*0 + 2*0 + 2*0 + 6*0 + 1*1 + 5*1 + 8*1 = 4
4*0 + 8*0 + 2*0 + 2*0 + 6*0 + 1*0 + 5*1 + 8*1 = 3
4*0 + 8*0 + 2*0 + 2*0 + 6*0 + 1*0 + 5*0 + 8*1 = 8
After 2 phases: 34040438
3*1 + 4*0 + 0*-1 + 4*0 + 0*1 + 4*0 + 3*-1 + 8*0 = 0
3*0 + 4*1 + 0*1 + 4*0 + 0*0 + 4*-1 + 3*-1 + 8*0 = 3
3*0 + 4*0 + 0*1 + 4*1 + 0*1 + 4*0 + 3*0 + 8*0 = 4
3*0 + 4*0 + 0*0 + 4*1 + 0*1 + 4*1 + 3*1 + 8*0 = 1
3*0 + 4*0 + 0*0 + 4*0 + 0*1 + 4*1 + 3*1 + 8*1 = 5
3*0 + 4*0 + 0*0 + 4*0 + 0*0 + 4*1 + 3*1 + 8*1 = 5
3*0 + 4*0 + 0*0 + 4*0 + 0*0 + 4*0 + 3*1 + 8*1 = 1
3*0 + 4*0 + 0*0 + 4*0 + 0*0 + 4*0 + 3*0 + 8*1 = 8
After 3 phases: 03415518
0*1 + 3*0 + 4*-1 + 1*0 + 5*1 + 5*0 + 1*-1 + 8*0 = 0
0*0 + 3*1 + 4*1 + 1*0 + 5*0 + 5*-1 + 1*-1 + 8*0 = 1
0*0 + 3*0 + 4*1 + 1*1 + 5*1 + 5*0 + 1*0 + 8*0 = 0
0*0 + 3*0 + 4*0 + 1*1 + 5*1 + 5*1 + 1*1 + 8*0 = 2
0*0 + 3*0 + 4*0 + 1*0 + 5*1 + 5*1 + 1*1 + 8*1 = 9
0*0 + 3*0 + 4*0 + 1*0 + 5*0 + 5*1 + 1*1 + 8*1 = 4
0*0 + 3*0 + 4*0 + 1*0 + 5*0 + 5*0 + 1*1 + 8*1 = 9
0*0 + 3*0 + 4*0 + 1*0 + 5*0 + 5*0 + 1*0 + 8*1 = 8
After 4 phases: 01029498
Here are the first eight digits of the final output list after 100 phases for some larger inputs:
• 80871224585914546619083218645595 becomes 24176176.
• 19617804207202209144916044189917 becomes 73745418.
• 69317163492948606335995924319873 becomes 52432133.
After 100 phases of FFT, what are the first eight digits in the final output list?
Your puzzle answer was 40921727.
--- Part Two ---
Now that your FFT is working, you can decode the real signal.
The real signal is your puzzle input repeated 10000 times. Treat this new signal as a single input list. Patterns are still
calculated as before, and 100 phases of FFT are still applied.
The first seven digits of your initial input signal also represent the message offset. The message offset is the location of
the eight-digit message in the final output list. Specifically, the message offset indicates the number of digits to skip
before reading the eight-digit message. For example, if the first seven digits of your initial input signal were 1234567, the
eight-digit message would be the eight digits after skipping 1,234,567 digits of the final output list. Or, if the message
offset were 7 and your final output list were 98765432109876543210, the eight-digit message would be 21098765. (Of course,
your real message offset will be a seven-digit number, not a one-digit number like 7.)
Here is the eight-digit message in the final output list after 100 phases. The message offset given in each input has been
highlighted. (Note that the inputs given below are repeated 10000 times to find the actual starting input lists.)
• 03036732577212944063491565474664 becomes 84462026.
• 02935109699940807407585447034323 becomes 78725270.
• 03081770884921959731165446850517 becomes 53553731.
After repeating your input signal 10000 times and running 100 phases of FFT, what is the eight-digit message embedded in the
final output list?
Your puzzle answer was 89950138.
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.
If you still want to see it, you can get your puzzle input.
References
Visible links
. https://adventofcode.com/
. https://adventofcode.com/2019/about
. https://adventofcode.com/2019/events
. https://adventofcode.com/2019/settings
. https://adventofcode.com/2019/auth/logout
. Advent of Code Supporter
https://adventofcode.com/2019/support
. https://adventofcode.com/2019
. https://adventofcode.com/2019
. https://adventofcode.com/2019/support
. https://adventofcode.com/2019/sponsors
. https://adventofcode.com/2019/leaderboard
. https://adventofcode.com/2019/stats
. https://adventofcode.com/2019/sponsors
. https://en.wikipedia.org/wiki/Gas_giant
. https://adventofcode.com/2019
. https://adventofcode.com/2019/day/16/input

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Advent of Code
--- Day 17: Set and Forget ---
An early warning system detects an incoming solar flare and automatically activates the ship's electromagnetic shield.
Unfortunately, this has cut off the Wi-Fi for many small robots that, unaware of the impending danger, are now trapped on
exterior scaffolding on the unsafe side of the shield. To rescue them, you'll have to act quickly!
The only tools at your disposal are some wired cameras and a small vacuum robot currently asleep at its charging station. The
video quality is poor, but the vacuum robot has a needlessly bright LED that makes it easy to spot no matter where it is.
An Intcode program, the Aft Scaffolding Control and Information Interface (ASCII, your puzzle input), provides access to the
cameras and the vacuum robot. Currently, because the vacuum robot is asleep, you can only access the cameras.
Running the ASCII program on your Intcode computer will provide the current view of the scaffolds. This is output, purely
coincidentally, as ASCII code: 35 means #, 46 means ., 10 starts a new line of output below the current one, and so on.
(Within a line, characters are drawn left-to-right.)
In the camera output, # represents a scaffold and . represents open space. The vacuum robot is visible as ^, v, <, or >
depending on whether it is facing up, down, left, or right respectively. When drawn like this, the vacuum robot is always on
a scaffold; if the vacuum robot ever walks off of a scaffold and begins tumbling through space uncontrollably, it will
instead be visible as X.
In general, the scaffold forms a path, but it sometimes loops back onto itself. For example, suppose you can see the
following view from the cameras:
..#..........
..#..........
#######...###
#.#...#...#.#
#############
..#...#...#..
..#####...^..
Here, the vacuum robot, ^ is facing up and sitting at one end of the scaffold near the bottom-right of the image. The
scaffold continues up, loops across itself several times, and ends at the top-left of the image.
The first step is to calibrate the cameras by getting the alignment parameters of some well-defined points. Locate all
scaffold intersections; for each, its alignment parameter is the distance between its left edge and the left edge of the view
multiplied by the distance between its top edge and the top edge of the view. Here, the intersections from the above image
are marked O:
..#..........
..#..........
##O####...###
#.#...#...#.#
##O###O###O##
..#...#...#..
..#####...^..
For these intersections:
• The top-left intersection is 2 units from the left of the image and 2 units from the top of the image, so its alignment
parameter is 2 * 2 = 4.
• The bottom-left intersection is 2 units from the left and 4 units from the top, so its alignment parameter is 2 * 4 = 8.
• The bottom-middle intersection is 6 from the left and 4 from the top, so its alignment parameter is 24.
• The bottom-right intersection's alignment parameter is 40.
To calibrate the cameras, you need the sum of the alignment parameters. In the above example, this is 76.
Run your ASCII program. What is the sum of the alignment parameters for the scaffold intersections?
Your puzzle answer was 3336.
--- Part Two ---
Now for the tricky part: notifying all the other robots about the solar flare. The vacuum robot can do this automatically if
it gets into range of a robot. However, you can't see the other robots on the camera, so you need to be thorough instead: you
need to make the vacuum robot visit every part of the scaffold at least once.
The vacuum robot normally wanders randomly, but there isn't time for that today. Instead, you can override its movement logic
with new rules.
Force the vacuum robot to wake up by changing the value in your ASCII program at address 0 from 1 to 2. When you do this, you
will be automatically prompted for the new movement rules that the vacuum robot should use. The ASCII program will use input
instructions to receive them, but they need to be provided as ASCII code; end each line of logic with a single newline, ASCII
code 10.
First, you will be prompted for the main movement routine. The main routine may only call the movement functions: A, B, or C.
Supply the movement functions to use as ASCII text, separating them with commas (,, ASCII code 44), and ending the list with
a newline (ASCII code 10). For example, to call A twice, then alternate between B and C three times, provide the string
A,A,B,C,B,C,B,C and then a newline.
Then, you will be prompted for each movement function. Movement functions may use L to turn left, R to turn right, or a
number to move forward that many units. Movement functions may not call other movement functions. Again, separate the actions
with commas and end the list with a newline. For example, to move forward 10 units, turn left, move forward 8 units, turn
right, and finally move forward 6 units, provide the string 10,L,8,R,6 and then a newline.
Finally, you will be asked whether you want to see a continuous video feed; provide either y or n and a newline. Enabling the
continuous video feed can help you see what's going on, but it also requires a significant amount of processing power, and
may even cause your Intcode computer to overheat.
Due to the limited amount of memory in the vacuum robot, the ASCII definitions of the main routine and the movement functions
may each contain at most 20 characters, not counting the newline.
For example, consider the following camera feed:
#######...#####
#.....#...#...#
#.....#...#...#
......#...#...#
......#...###.#
......#.....#.#
^########...#.#
......#.#...#.#
......#########
........#...#..
....#########..
....#...#......
....#...#......
....#...#......
....#####......
In order for the vacuum robot to visit every part of the scaffold at least once, one path it could take is:
R,8,R,8,R,4,R,4,R,8,L,6,L,2,R,4,R,4,R,8,R,8,R,8,L,6,L,2
Without the memory limit, you could just supply this whole string to function A and have the main routine call A once.
However, you'll need to split it into smaller parts.
One approach is:
• Main routine: A,B,C,B,A,C
(ASCII input: 65, 44, 66, 44, 67, 44, 66, 44, 65, 44, 67, 10)
• Function A:   R,8,R,8
(ASCII input: 82, 44, 56, 44, 82, 44, 56, 10)
• Function B:   R,4,R,4,R,8
(ASCII input: 82, 44, 52, 44, 82, 44, 52, 44, 82, 44, 56, 10)
• Function C:   L,6,L,2
(ASCII input: 76, 44, 54, 44, 76, 44, 50, 10)
Visually, this would break the desired path into the following parts:
A, B, C, B, A, C
R,8,R,8, R,4,R,4,R,8, L,6,L,2, R,4,R,4,R,8, R,8,R,8, L,6,L,2
CCCCCCA...BBBBB
C.....A...B...B
C.....A...B...B
......A...B...B
......A...CCC.B
......A.....C.B
^AAAAAAAA...C.B
......A.A...C.B
......AAAAAA#AB
........A...C..
....BBBB#BBBB..
....B...A......
....B...A......
....B...A......
....BBBBA......
Of course, the scaffolding outside your ship is much more complex.
As the vacuum robot finds other robots and notifies them of the impending solar flare, it also can't help but leave them
squeaky clean, collecting any space dust it finds. Once it finishes the programmed set of movements, assuming it hasn't
drifted off into space, the cleaning robot will return to its docking station and report the amount of space dust it
collected as a large, non-ASCII value in a single output instruction.
After visiting every part of the scaffold at least once, how much dust does the vacuum robot report it has collected?
Your puzzle answer was 597517.
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.
If you still want to see it, you can get your puzzle input.
References
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. https://en.wikipedia.org/wiki/Solar_flare
. https://adventofcode.com/2019/day/9
. https://simple.wikipedia.org/wiki/ASCII
. https://en.wikipedia.org/wiki/Newline#In_programming_languages
. https://adventofcode.com/2019
. https://adventofcode.com/2019/day/17/input

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Advent of Code
--- Day 18: Many-Worlds Interpretation ---
As you approach Neptune, a planetary security system detects you and activates a giant tractor beam on Triton! You have no
choice but to land.
A scan of the local area reveals only one interesting feature: a massive underground vault. You generate a map of the tunnels
(your puzzle input). The tunnels are too narrow to move diagonally.
Only one entrance (marked @) is present among the open passages (marked .) and stone walls (#), but you also detect an
assortment of keys (shown as lowercase letters) and doors (shown as uppercase letters). Keys of a given letter open the door
of the same letter: a opens A, b opens B, and so on. You aren't sure which key you need to disable the tractor beam, so
you'll need to collect all of them.
For example, suppose you have the following map:
#########
#b.A.@.a#
#########
Starting from the entrance (@), you can only access a large door (A) and a key (a). Moving toward the door doesn't help you,
but you can move 2 steps to collect the key, unlocking A in the process:
#########
#b.....@#
#########
Then, you can move 6 steps to collect the only other key, b:
#########
#@......#
#########
So, collecting every key took a total of 8 steps.
Here is a larger example:
########################
#f.D.E.e.C.b.A.@.a.B.c.#
######################.#
#d.....................#
########################
The only reasonable move is to take key a and unlock door A:
########################
#f.D.E.e.C.b.....@.B.c.#
######################.#
#d.....................#
########################
Then, do the same with key b:
########################
#f.D.E.e.C.@.........c.#
######################.#
#d.....................#
########################
...and the same with key c:
########################
#f.D.E.e.............@.#
######################.#
#d.....................#
########################
Now, you have a choice between keys d and e. While key e is closer, collecting it now would be slower in the long run than
collecting key d first, so that's the best choice:
########################
#f...E.e...............#
######################.#
#@.....................#
########################
Finally, collect key e to unlock door E, then collect key f, taking a grand total of 86 steps.
Here are a few more examples:
• ########################
#...............b.C.D.f#
#.######################
#.....@.a.B.c.d.A.e.F.g#
########################
Shortest path is 132 steps: b, a, c, d, f, e, g
• #################
#i.G..c...e..H.p#
########.########
#j.A..b...f..D.o#
########@########
#k.E..a...g..B.n#
########.########
#l.F..d...h..C.m#
#################
Shortest paths are 136 steps;
one is: a, f, b, j, g, n, h, d, l, o, e, p, c, i, k, m
• ########################
#@..............ac.GI.b#
###d#e#f################
###A#B#C################
###g#h#i################
########################
Shortest paths are 81 steps; one is: a, c, f, i, d, g, b, e, h
How many steps is the shortest path that collects all of the keys?
Your puzzle answer was 4270.
--- Part Two ---
You arrive at the vault only to discover that there is not one vault, but four - each with its own entrance.
On your map, find the area in the middle that looks like this:
...
.@.
...
Update your map to instead use the correct data:
@#@
###
@#@
This change will split your map into four separate sections, each with its own entrance:
####### #######
#a.#Cd# #a.#Cd#
##...## ##@#@##
##.@.## --> #######
##...## ##@#@##
#cB#Ab# #cB#Ab#
####### #######
Because some of the keys are for doors in other vaults, it would take much too long to collect all of the keys by yourself.
Instead, you deploy four remote-controlled robots. Each starts at one of the entrances (@).
Your goal is still to collect all of the keys in the fewest steps, but now, each robot has its own position and can move
independently. You can only remotely control a single robot at a time. Collecting a key instantly unlocks any corresponding
doors, regardless of the vault in which the key or door is found.
For example, in the map above, the top-left robot first collects key a, unlocking door A in the bottom-right vault:
#######
#@.#Cd#
##.#@##
#######
##@#@##
#cB#.b#
#######
Then, the bottom-right robot collects key b, unlocking door B in the bottom-left vault:
#######
#@.#Cd#
##.#@##
#######
##@#.##
#c.#.@#
#######
Then, the bottom-left robot collects key c:
#######
#@.#.d#
##.#@##
#######
##.#.##
#@.#.@#
#######
Finally, the top-right robot collects key d:
#######
#@.#.@#
##.#.##
#######
##.#.##
#@.#.@#
#######
In this example, it only took 8 steps to collect all of the keys.
Sometimes, multiple robots might have keys available, or a robot might have to wait for multiple keys to be collected:
###############
#d.ABC.#.....a#
######@#@######
###############
######@#@######
#b.....#.....c#
###############
First, the top-right, bottom-left, and bottom-right robots take turns collecting keys a, b, and c, a total of 6 + 6 + 6 = 18
steps. Then, the top-left robot can access key d, spending another 6 steps; collecting all of the keys here takes a minimum
of 24 steps.
Here's a more complex example:
#############
#DcBa.#.GhKl#
#.###@#@#I###
#e#d#####j#k#
###C#@#@###J#
#fEbA.#.FgHi#
#############
• Top-left robot collects key a.
• Bottom-left robot collects key b.
• Top-left robot collects key c.
• Bottom-left robot collects key d.
• Top-left robot collects key e.
• Bottom-left robot collects key f.
• Bottom-right robot collects key g.
• Top-right robot collects key h.
• Bottom-right robot collects key i.
• Top-right robot collects key j.
• Bottom-right robot collects key k.
• Top-right robot collects key l.
In the above example, the fewest steps to collect all of the keys is 32.
Here's an example with more choices:
#############
#g#f.D#..h#l#
#F###e#E###.#
#dCba@#@BcIJ#
#############
#nK.L@#@G...#
#M###N#H###.#
#o#m..#i#jk.#
#############
One solution with the fewest steps is:
• Top-left robot collects key e.
• Top-right robot collects key h.
• Bottom-right robot collects key i.
• Top-left robot collects key a.
• Top-left robot collects key b.
• Top-right robot collects key c.
• Top-left robot collects key d.
• Top-left robot collects key f.
• Top-left robot collects key g.
• Bottom-right robot collects key k.
• Bottom-right robot collects key j.
• Top-right robot collects key l.
• Bottom-left robot collects key n.
• Bottom-left robot collects key m.
• Bottom-left robot collects key o.
This example requires at least 72 steps to collect all keys.
After updating your map and using the remote-controlled robots, what is the fewest steps necessary to collect all of the
keys?
Your puzzle answer was 1982.
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.
If you still want to see it, you can get your puzzle input.
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Advent of Code
--- Day 19: Tractor Beam ---
Unsure of the state of Santa's ship, you borrowed the tractor beam technology from Triton. Time to test it out.
When you're safely away from anything else, you activate the tractor beam, but nothing happens. It's hard to tell whether
it's working if there's nothing to use it on. Fortunately, your ship's drone system can be configured to deploy a drone to
specific coordinates and then check whether it's being pulled. There's even an Intcode program (your puzzle input) that gives
you access to the drone system.
The program uses two input instructions to request the X and Y position to which the drone should be deployed. Negative
numbers are invalid and will confuse the drone; all numbers should be zero or positive.
Then, the program will output whether the drone is stationary (0) or being pulled by something (1). For example, the
coordinate X=0, Y=0 is directly in front of the tractor beam emitter, so the drone control program will always report 1 at
that location.
To better understand the tractor beam, it is important to get a good picture of the beam itself. For example, suppose you
scan the 10x10 grid of points closest to the emitter:
X
0-> 9
0#.........
|.#........
v..##......
...###....
....###...
Y .....####.
......####
......####
.......###
9........##
In this example, the number of points affected by the tractor beam in the 10x10 area closest to the emitter is 27.
However, you'll need to scan a larger area to understand the shape of the beam. How many points are affected by the tractor
beam in the 50x50 area closest to the emitter? (For each of X and Y, this will be 0 through 49.)
Your puzzle answer was 217.
--- Part Two ---
You aren't sure how large Santa's ship is. You aren't even sure if you'll need to use this thing on Santa's ship, but it
doesn't hurt to be prepared. You figure Santa's ship might fit in a 100x100 square.
The beam gets wider as it travels away from the emitter; you'll need to be a minimum distance away to fit a square of that
size into the beam fully. (Don't rotate the square; it should be aligned to the same axes as the drone grid.)
For example, suppose you have the following tractor beam readings:
#.......................................
.#......................................
..##....................................
...###..................................
....###.................................
.....####...............................
......#####.............................
......######............................
.......#######..........................
........########........................
.........#########......................
..........#########.....................
...........##########...................
...........############.................
............############................
.............#############..............
..............##############............
...............###############..........
................###############.........
................#################.......
.................########OOOOOOOOOO.....
..................#######OOOOOOOOOO#....
...................######OOOOOOOOOO###..
....................#####OOOOOOOOOO#####
.....................####OOOOOOOOOO#####
.....................####OOOOOOOOOO#####
......................###OOOOOOOOOO#####
.......................##OOOOOOOOOO#####
........................#OOOOOOOOOO#####
.........................OOOOOOOOOO#####
..........................##############
..........................##############
...........................#############
............................############
.............................###########
In this example, the 10x10 square closest to the emitter that fits entirely within the tractor beam has been marked O. Within
it, the point closest to the emitter (the only highlighted O) is at X=25, Y=20.
Find the 100x100 square closest to the emitter that fits entirely within the tractor beam; within that square, find the point
closest to the emitter. What value do you get if you take that point's X coordinate, multiply it by 10000, then add the
point's Y coordinate? (In the example above, this would be 250020.)
Your puzzle answer was 6840937.
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.
If you still want to see it, you can get your puzzle input.
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Advent of Code
--- Day 20: Donut Maze ---
You notice a strange pattern on the surface of Pluto and land nearby to get a closer look. Upon closer inspection, you
realize you've come across one of the famous space-warping mazes of the long-lost Pluto civilization!
Because there isn't much space on Pluto, the civilization that used to live here thrived by inventing a method for folding
spacetime. Although the technology is no longer understood, mazes like this one provide a small glimpse into the daily life
of an ancient Pluto citizen.
This maze is shaped like a donut. Portals along the inner and outer edge of the donut can instantly teleport you from one
side to the other. For example:
A
A
#######.#########
#######.........#
#######.#######.#
#######.#######.#
#######.#######.#
##### B ###.#
BC...## C ###.#
##.## ###.#
##...DE F ###.#
##### G ###.#
#########.#####.#
DE..#######...###.#
#.#########.###.#
FG..#########.....#
###########.#####
Z
Z
This map of the maze shows solid walls (#) and open passages (.). Every maze on Pluto has a start (the open tile next to AA)
and an end (the open tile next to ZZ). Mazes on Pluto also have portals; this maze has three pairs of portals: BC, DE, and
FG. When on an open tile next to one of these labels, a single step can take you to the other tile with the same label. (You
can only walk on . tiles; labels and empty space are not traversable.)
One path through the maze doesn't require any portals. Starting at AA, you could go down 1, right 8, down 12, left 4, and
down 1 to reach ZZ, a total of 26 steps.
However, there is a shorter path: You could walk from AA to the inner BC portal (4 steps), warp to the outer BC portal (1
step), walk to the inner DE (6 steps), warp to the outer DE (1 step), walk to the outer FG (4 steps), warp to the inner FG (1
step), and finally walk to ZZ (6 steps). In total, this is only 23 steps.
Here is a larger example:
A
A
#################.#############
#.#...#...................#.#.#
#.#.#.###.###.###.#########.#.#
#.#.#.......#...#.....#.#.#...#
#.#########.###.#####.#.#.###.#
#.............#.#.....#.......#
###.###########.###.#####.#.#.#
#.....# A C #.#.#.#
####### S P #####.#
#.#...# #......VT
#.#.#.# #.#####
#...#.# YN....#.#
#.###.# #####.#
DI....#.# #.....#
#####.# #.###.#
ZZ......# QG....#..AS
###.### #######
JO..#.#.# #.....#
#.#.#.# ###.#.#
#...#..DI BU....#..LF
#####.# #.#####
YN......# VT..#....QG
#.###.# #.###.#
#.#...# #.....#
###.### J L J #.#.###
#.....# O F P #.#...#
#.###.#####.#.#####.#####.###.#
#...#.#.#...#.....#.....#.#...#
#.#####.###.###.#.#.#########.#
#...#.#.....#...#.#.#.#.....#.#
#.###.#####.###.###.#.#.#######
#.#.........#...#.............#
#########.###.###.#############
B J C
U P P
Here, AA has no direct path to ZZ, but it does connect to AS and CP. By passing through AS, QG, BU, and JO, you can reach ZZ
in 58 steps.
In your maze, how many steps does it take to get from the open tile marked AA to the open tile marked ZZ?
Your puzzle answer was 552.
--- Part Two ---
Strangely, the exit isn't open when you reach it. Then, you remember: the ancient Plutonians were famous for building
recursive spaces.
The marked connections in the maze aren't portals: they physically connect to a larger or smaller copy of the maze.
Specifically, the labeled tiles around the inside edge actually connect to a smaller copy of the same maze, and the smaller
copy's inner labeled tiles connect to yet a smaller copy, and so on.
When you enter the maze, you are at the outermost level; when at the outermost level, only the outer labels AA and ZZ
function (as the start and end, respectively); all other outer labeled tiles are effectively walls. At any other level, AA
and ZZ count as walls, but the other outer labeled tiles bring you one level outward.
Your goal is to find a path through the maze that brings you back to ZZ at the outermost level of the maze.
In the first example above, the shortest path is now the loop around the right side. If the starting level is 0, then taking
the previously-shortest path would pass through BC (to level 1), DE (to level 2), and FG (back to level 1). Because this is
not the outermost level, ZZ is a wall, and the only option is to go back around to BC, which would only send you even deeper
into the recursive maze.
In the second example above, there is no path that brings you to ZZ at the outermost level.
Here is a more interesting example:
Z L X W C
Z P Q B K
###########.#.#.#.#######.###############
#...#.......#.#.......#.#.......#.#.#...#
###.#.#.#.#.#.#.#.###.#.#.#######.#.#.###
#.#...#.#.#...#.#.#...#...#...#.#.......#
#.###.#######.###.###.#.###.###.#.#######
#...#.......#.#...#...#.............#...#
#.#########.#######.#.#######.#######.###
#...#.# F R I Z #.#.#.#
#.###.# D E C H #.#.#.#
#.#...# #...#.#
#.###.# #.###.#
#.#....OA WB..#.#..ZH
#.###.# #.#.#.#
CJ......# #.....#
####### #######
#.#....CK #......IC
#.###.# #.###.#
#.....# #...#.#
###.### #.#.#.#
XF....#.# RF..#.#.#
#####.# #######
#......CJ NM..#...#
###.#.# #.###.#
RE....#.# #......RF
###.### X X L #.#.#.#
#.....# F Q P #.#.#.#
###.###########.###.#######.#########.###
#.....#...#.....#.......#...#.....#.#...#
#####.#.###.#######.#######.###.###.#.#.#
#.......#.......#.#.#.#.#...#...#...#.#.#
#####.###.#####.#.#.#.#.###.###.#.###.###
#.......#.....#.#...#...............#...#
#############.#.#.###.###################
A O F N
A A D M
One shortest path through the maze is the following:
• Walk from AA to XF (16 steps)
• Recurse into level 1 through XF (1 step)
• Walk from XF to CK (10 steps)
• Recurse into level 2 through CK (1 step)
• Walk from CK to ZH (14 steps)
• Recurse into level 3 through ZH (1 step)
• Walk from ZH to WB (10 steps)
• Recurse into level 4 through WB (1 step)
• Walk from WB to IC (10 steps)
• Recurse into level 5 through IC (1 step)
• Walk from IC to RF (10 steps)
• Recurse into level 6 through RF (1 step)
• Walk from RF to NM (8 steps)
• Recurse into level 7 through NM (1 step)
• Walk from NM to LP (12 steps)
• Recurse into level 8 through LP (1 step)
• Walk from LP to FD (24 steps)
• Recurse into level 9 through FD (1 step)
• Walk from FD to XQ (8 steps)
• Recurse into level 10 through XQ (1 step)
• Walk from XQ to WB (4 steps)
• Return to level 9 through WB (1 step)
• Walk from WB to ZH (10 steps)
• Return to level 8 through ZH (1 step)
• Walk from ZH to CK (14 steps)
• Return to level 7 through CK (1 step)
• Walk from CK to XF (10 steps)
• Return to level 6 through XF (1 step)
• Walk from XF to OA (14 steps)
• Return to level 5 through OA (1 step)
• Walk from OA to CJ (8 steps)
• Return to level 4 through CJ (1 step)
• Walk from CJ to RE (8 steps)
• Return to level 3 through RE (1 step)
• Walk from RE to IC (4 steps)
• Recurse into level 4 through IC (1 step)
• Walk from IC to RF (10 steps)
• Recurse into level 5 through RF (1 step)
• Walk from RF to NM (8 steps)
• Recurse into level 6 through NM (1 step)
• Walk from NM to LP (12 steps)
• Recurse into level 7 through LP (1 step)
• Walk from LP to FD (24 steps)
• Recurse into level 8 through FD (1 step)
• Walk from FD to XQ (8 steps)
• Recurse into level 9 through XQ (1 step)
• Walk from XQ to WB (4 steps)
• Return to level 8 through WB (1 step)
• Walk from WB to ZH (10 steps)
• Return to level 7 through ZH (1 step)
• Walk from ZH to CK (14 steps)
• Return to level 6 through CK (1 step)
• Walk from CK to XF (10 steps)
• Return to level 5 through XF (1 step)
• Walk from XF to OA (14 steps)
• Return to level 4 through OA (1 step)
• Walk from OA to CJ (8 steps)
• Return to level 3 through CJ (1 step)
• Walk from CJ to RE (8 steps)
• Return to level 2 through RE (1 step)
• Walk from RE to XQ (14 steps)
• Return to level 1 through XQ (1 step)
• Walk from XQ to FD (8 steps)
• Return to level 0 through FD (1 step)
• Walk from FD to ZZ (18 steps)
This path takes a total of 396 steps to move from AA at the outermost layer to ZZ at the outermost layer.
In your maze, when accounting for recursion, how many steps does it take to get from the open tile marked AA to the open tile
marked ZZ, both at the outermost layer?
Your puzzle answer was 6492.
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.
If you still want to see it, you can get your puzzle input.
References
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Advent of Code
--- Day 21: Springdroid Adventure ---
You lift off from Pluto and start flying in the direction of Santa.
While experimenting further with the tractor beam, you accidentally pull an asteroid directly into your ship! It deals
significant damage to your hull and causes your ship to begin tumbling violently.
You can send a droid out to investigate, but the tumbling is causing enough artificial gravity that one wrong step could send
the droid through a hole in the hull and flying out into space.
The clear choice for this mission is a droid that can jump over the holes in the hull - a springdroid.
You can use an Intcode program (your puzzle input) running on an ASCII-capable computer to program the springdroid. However,
springdroids don't run Intcode; instead, they run a simplified assembly language called springscript.
While a springdroid is certainly capable of navigating the artificial gravity and giant holes, it has one downside: it can
only remember at most 15 springscript instructions.
The springdroid will move forward automatically, constantly thinking about whether to jump. The springscript program defines
the logic for this decision.
Springscript programs only use Boolean values, not numbers or strings. Two registers are available: T, the temporary value
register, and J, the jump register. If the jump register is true at the end of the springscript program, the springdroid will
try to jump. Both of these registers start with the value false.
Springdroids have a sensor that can detect whether there is ground at various distances in the direction it is facing; these
values are provided in read-only registers. Your springdroid can detect ground at four distances: one tile away (A), two
tiles away (B), three tiles away (C), and four tiles away (D). If there is ground at the given distance, the register will be
true; if there is a hole, the register will be false.
There are only three instructions available in springscript:
• AND X Y sets Y to true if both X and Y are true; otherwise, it sets Y to false.
• OR X Y sets Y to true if at least one of X or Y is true; otherwise, it sets Y to false.
• NOT X Y sets Y to true if X is false; otherwise, it sets Y to false.
In all three instructions, the second argument (Y) needs to be a writable register (either T or J). The first argument (X)
can be any register (including A, B, C, or D).
For example, the one-instruction program NOT A J means "if the tile immediately in front of me is not ground, jump".
Or, here is a program that jumps if a three-tile-wide hole (with ground on the other side of the hole) is detected:
NOT A J
NOT B T
AND T J
NOT C T
AND T J
AND D J
The Intcode program expects ASCII inputs and outputs. It will begin by displaying a prompt; then, input the desired
instructions one per line. End each line with a newline (ASCII code 10). When you have finished entering your program,
provide the command WALK followed by a newline to instruct the springdroid to begin surveying the hull.
If the springdroid falls into space, an ASCII rendering of the last moments of its life will be produced. In these, @ is the
springdroid, # is hull, and . is empty space. For example, suppose you program the springdroid like this:
NOT D J
WALK
This one-instruction program sets J to true if and only if there is no ground four tiles away. In other words, it attempts to
jump into any hole it finds:
.................
.................
@................
#####.###########
.................
.................
.@...............
#####.###########
.................
..@..............
.................
#####.###########
...@.............
.................
.................
#####.###########
.................
....@............
.................
#####.###########
.................
.................
.....@...........
#####.###########
.................
.................
.................
#####@###########
However, if the springdroid successfully makes it across, it will use an output instruction to indicate the amount of damage
to the hull as a single giant integer outside the normal ASCII range.
Program the springdroid with logic that allows it to survey the hull without falling into space. What amount of hull damage
does it report?
Your puzzle answer was 19354818.
--- Part Two ---
There are many areas the springdroid can't reach. You flip through the manual and discover a way to increase its sensor
range.
Instead of ending your springcode program with WALK, use RUN. Doing this will enable extended sensor mode, capable of sensing
ground up to nine tiles away. This data is available in five new read-only registers:
• Register E indicates whether there is ground five tiles away.
• Register F indicates whether there is ground six tiles away.
• Register G indicates whether there is ground seven tiles away.
• Register H indicates whether there is ground eight tiles away.
• Register I indicates whether there is ground nine tiles away.
All other functions remain the same.
Successfully survey the rest of the hull by ending your program with RUN. What amount of hull damage does the springdroid now
report?
Your puzzle answer was 1143787220.
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.
If you still want to see it, you can get your puzzle input.
References
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. https://en.wikipedia.org/wiki/Programmable_read-only_memory
. https://en.wikipedia.org/wiki/Boolean_data_type
. https://adventofcode.com/2019
. https://adventofcode.com/2019/day/21/input

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Advent of Code
--- Day 22: Slam Shuffle ---
There isn't much to do while you wait for the droids to repair your ship. At least you're drifting in the right direction.
You decide to practice a new card shuffle you've been working on.
Digging through the ship's storage, you find a deck of space cards! Just like any deck of space cards, there are 10007 cards
in the deck numbered 0 through 10006. The deck must be new - they're still in factory order, with 0 on the top, then 1, then
2, and so on, all the way through to 10006 on the bottom.
You've been practicing three different techniques that you use while shuffling. Suppose you have a deck of only 10 cards
(numbered 0 through 9):
To deal into new stack, create a new stack of cards by dealing the top card of the deck onto the top of the new stack
repeatedly until you run out of cards:
Top Bottom
0 1 2 3 4 5 6 7 8 9 Your deck
New stack
1 2 3 4 5 6 7 8 9 Your deck
0 New stack
2 3 4 5 6 7 8 9 Your deck
1 0 New stack
3 4 5 6 7 8 9 Your deck
2 1 0 New stack
Several steps later...
9 Your deck
8 7 6 5 4 3 2 1 0 New stack
Your deck
9 8 7 6 5 4 3 2 1 0 New stack
Finally, pick up the new stack you've just created and use it as the deck for the next technique.
To cut N cards, take the top N cards off the top of the deck and move them as a single unit to the bottom of the deck,
retaining their order. For example, to cut 3:
Top Bottom
0 1 2 3 4 5 6 7 8 9 Your deck
3 4 5 6 7 8 9 Your deck
0 1 2 Cut cards
3 4 5 6 7 8 9 Your deck
0 1 2 Cut cards
3 4 5 6 7 8 9 0 1 2 Your deck
You've also been getting pretty good at a version of this technique where N is negative! In that case, cut (the absolute
value of) N cards from the bottom of the deck onto the top. For example, to cut -4:
Top Bottom
0 1 2 3 4 5 6 7 8 9 Your deck
0 1 2 3 4 5 Your deck
6 7 8 9 Cut cards
0 1 2 3 4 5 Your deck
6 7 8 9 Cut cards
6 7 8 9 0 1 2 3 4 5 Your deck
To deal with increment N, start by clearing enough space on your table to lay out all of the cards individually in a long
line. Deal the top card into the leftmost position. Then, move N positions to the right and deal the next card there. If you
would move into a position past the end of the space on your table, wrap around and keep counting from the leftmost card
again. Continue this process until you run out of cards.
For example, to deal with increment 3:
0 1 2 3 4 5 6 7 8 9 Your deck
. . . . . . . . . . Space on table
^ Current position
Deal the top card to the current position:
1 2 3 4 5 6 7 8 9 Your deck
0 . . . . . . . . . Space on table
^ Current position
Move the current position right 3:
1 2 3 4 5 6 7 8 9 Your deck
0 . . . . . . . . . Space on table
^ Current position
Deal the top card:
2 3 4 5 6 7 8 9 Your deck
0 . . 1 . . . . . . Space on table
^ Current position
Move right 3 and deal:
3 4 5 6 7 8 9 Your deck
0 . . 1 . . 2 . . . Space on table
^ Current position
Move right 3 and deal:
4 5 6 7 8 9 Your deck
0 . . 1 . . 2 . . 3 Space on table
^ Current position
Move right 3, wrapping around, and deal:
5 6 7 8 9 Your deck
0 . 4 1 . . 2 . . 3 Space on table
^ Current position
And so on:
0 7 4 1 8 5 2 9 6 3 Space on table
Positions on the table which already contain cards are still counted; they're not skipped. Of course, this technique is
carefully designed so it will never put two cards in the same position or leave a position empty.
Finally, collect the cards on the table so that the leftmost card ends up at the top of your deck, the card to its right ends
up just below the top card, and so on, until the rightmost card ends up at the bottom of the deck.
The complete shuffle process (your puzzle input) consists of applying many of these techniques. Here are some examples that
combine techniques; they all start with a factory order deck of 10 cards:
deal with increment 7
deal into new stack
deal into new stack
Result: 0 3 6 9 2 5 8 1 4 7
cut 6
deal with increment 7
deal into new stack
Result: 3 0 7 4 1 8 5 2 9 6
deal with increment 7
deal with increment 9
cut -2
Result: 6 3 0 7 4 1 8 5 2 9
deal into new stack
cut -2
deal with increment 7
cut 8
cut -4
deal with increment 7
cut 3
deal with increment 9
deal with increment 3
cut -1
Result: 9 2 5 8 1 4 7 0 3 6
Positions within the deck count from 0 at the top, then 1 for the card immediately below the top card, and so on to the
bottom. (That is, cards start in the position matching their number.)
After shuffling your factory order deck of 10007 cards, what is the position of card 2019?
Your puzzle answer was 6129.
--- Part Two ---
After a while, you realize your shuffling skill won't improve much more with merely a single deck of cards. You ask every 3D
printer on the ship to make you some more cards while you check on the ship repairs. While reviewing the work the droids have
finished so far, you think you see Halley's Comet fly past!
When you get back, you discover that the 3D printers have combined their power to create for you a single, giant, brand new,
factory order deck of 119315717514047 space cards.
Finally, a deck of cards worthy of shuffling!
You decide to apply your complete shuffle process (your puzzle input) to the deck 101741582076661 times in a row.
You'll need to be careful, though - one wrong move with this many cards and you might overflow your entire ship!
After shuffling your new, giant, factory order deck that many times, what number is on the card that ends up in position
2020?
Your puzzle answer was 71345377301237.
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.
If you still want to see it, you can get your puzzle input.
References
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. https://adventofcode.com/2019
. https://adventofcode.com/2019/day/22/input

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Advent of Code
--- Day 23: Category Six ---
The droids have finished repairing as much of the ship as they can. Their report indicates that this was a Category 6
disaster - not because it was that bad, but because it destroyed the stockpile of Category 6 network cables as well as most
of the ship's network infrastructure.
You'll need to rebuild the network from scratch.
The computers on the network are standard Intcode computers that communicate by sending packets to each other. There are 50
of them in total, each running a copy of the same Network Interface Controller (NIC) software (your puzzle input). The
computers have network addresses 0 through 49; when each computer boots up, it will request its network address via a single
input instruction. Be sure to give each computer a unique network address.
Once a computer has received its network address, it will begin doing work and communicating over the network by sending and
receiving packets. All packets contain two values named X and Y. Packets sent to a computer are queued by the recipient and
read in the order they are received.
To send a packet to another computer, the NIC will use three output instructions that provide the destination address of the
packet followed by its X and Y values. For example, three output instructions that provide the values 10, 20, 30 would send a
packet with X=20 and Y=30 to the computer with address 10.
To receive a packet from another computer, the NIC will use an input instruction. If the incoming packet queue is empty,
provide -1. Otherwise, provide the X value of the next packet; the computer will then use a second input instruction to
receive the Y value for the same packet. Once both values of the packet are read in this way, the packet is removed from the
queue.
Note that these input and output instructions never block. Specifically, output instructions do not wait for the sent packet
to be received - the computer might send multiple packets before receiving any. Similarly, input instructions do not wait for
a packet to arrive - if no packet is waiting, input instructions should receive -1.
Boot up all 50 computers and attach them to your network. What is the Y value of the first packet sent to address 255?
Your puzzle answer was 19530.
--- Part Two ---
Packets sent to address 255 are handled by a device called a NAT (Not Always Transmitting). The NAT is responsible for
managing power consumption of the network by blocking certain packets and watching for idle periods in the computers.
If a packet would be sent to address 255, the NAT receives it instead. The NAT remembers only the last packet it receives;
that is, the data in each packet it receives overwrites the NAT's packet memory with the new packet's X and Y values.
The NAT also monitors all computers on the network. If all computers have empty incoming packet queues and are continuously
trying to receive packets without sending packets, the network is considered idle.
Once the network is idle, the NAT sends only the last packet it received to address 0; this will cause the computers on the
network to resume activity. In this way, the NAT can throttle power consumption of the network when the ship needs power in
other areas.
Monitor packets released to the computer at address 0 by the NAT. What is the first Y value delivered by the NAT to the
computer at address 0 twice in a row?
Your puzzle answer was 12725.
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.
If you still want to see it, you can get your puzzle input.
References
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Advent of Code
--- Day 24: Planet of Discord ---
You land on Eris, your last stop before reaching Santa. As soon as you do, your sensors start picking up strange life forms
moving around: Eris is infested with bugs! With an over 24-hour roundtrip for messages between you and Earth, you'll have to
deal with this problem on your own.
Eris isn't a very large place; a scan of the entire area fits into a 5x5 grid (your puzzle input). The scan shows bugs (#)
and empty spaces (.).
Each minute, The bugs live and die based on the number of bugs in the four adjacent tiles:
• A bug dies (becoming an empty space) unless there is exactly one bug adjacent to it.
• An empty space becomes infested with a bug if exactly one or two bugs are adjacent to it.
Otherwise, a bug or empty space remains the same. (Tiles on the edges of the grid have fewer than four adjacent tiles; the
missing tiles count as empty space.) This process happens in every location simultaneously; that is, within the same minute,
the number of adjacent bugs is counted for every tile first, and then the tiles are updated.
Here are the first few minutes of an example scenario:
Initial state:
....#
#..#.
#..##
..#..
#....
After 1 minute:
#..#.
####.
###.#
##.##
.##..
After 2 minutes:
#####
....#
....#
...#.
#.###
After 3 minutes:
#....
####.
...##
#.##.
.##.#
After 4 minutes:
####.
....#
##..#
.....
##...
To understand the nature of the bugs, watch for the first time a layout of bugs and empty spaces matches any previous layout.
In the example above, the first layout to appear twice is:
.....
.....
.....
#....
.#...
To calculate the biodiversity rating for this layout, consider each tile left-to-right in the top row, then left-to-right in
the second row, and so on. Each of these tiles is worth biodiversity points equal to increasing powers of two: 1, 2, 4, 8,
16, 32, and so on. Add up the biodiversity points for tiles with bugs; in this example, the 16th tile (32768 points) and 22nd
tile (2097152 points) have bugs, a total biodiversity rating of 2129920.
What is the biodiversity rating for the first layout that appears twice?
Your puzzle answer was 17321586.
--- Part Two ---
After careful analysis, one thing is certain: you have no idea where all these bugs are coming from.
Then, you remember: Eris is an old Plutonian settlement! Clearly, the bugs are coming from recursively-folded space.
This 5x5 grid is only one level in an infinite number of recursion levels. The tile in the middle of the grid is actually
another 5x5 grid, the grid in your scan is contained as the middle tile of a larger 5x5 grid, and so on. Two levels of grids
look like this:
| | | |
| | | |
| | | |
-----+-----+---------+-----+-----
| | | |
| | | |
| | | |
-----+-----+---------+-----+-----
| | | | | | | |
| |-+-+-+-+-| |
| | | | | | | |
| |-+-+-+-+-| |
| | | |?| | | |
| |-+-+-+-+-| |
| | | | | | | |
| |-+-+-+-+-| |
| | | | | | | |
-----+-----+---------+-----+-----
| | | |
| | | |
| | | |
-----+-----+---------+-----+-----
| | | |
| | | |
| | | |
(To save space, some of the tiles are not drawn to scale.) Remember, this is only a small part of the infinitely recursive
grid; there is a 5x5 grid that contains this diagram, and a 5x5 grid that contains that one, and so on. Also, the ? in the
diagram contains another 5x5 grid, which itself contains another 5x5 grid, and so on.
The scan you took (your puzzle input) shows where the bugs are on a single level of this structure. The middle tile of your
scan is empty to accommodate the recursive grids within it. Initially, no other levels contain bugs.
Tiles still count as adjacent if they are directly up, down, left, or right of a given tile. Some tiles have adjacent tiles
at a recursion level above or below its own level. For example:
| | | |
1 | 2 | 3 | 4 | 5
| | | |
-----+-----+---------+-----+-----
| | | |
6 | 7 | 8 | 9 | 10
| | | |
-----+-----+---------+-----+-----
| |A|B|C|D|E| |
| |-+-+-+-+-| |
| |F|G|H|I|J| |
| |-+-+-+-+-| |
11 | 12 |K|L|?|N|O| 14 | 15
| |-+-+-+-+-| |
| |P|Q|R|S|T| |
| |-+-+-+-+-| |
| |U|V|W|X|Y| |
-----+-----+---------+-----+-----
| | | |
16 | 17 | 18 | 19 | 20
| | | |
-----+-----+---------+-----+-----
| | | |
21 | 22 | 23 | 24 | 25
| | | |
• Tile 19 has four adjacent tiles: 14, 18, 20, and 24.
• Tile G has four adjacent tiles: B, F, H, and L.
• Tile D has four adjacent tiles: 8, C, E, and I.
• Tile E has four adjacent tiles: 8, D, 14, and J.
• Tile 14 has eight adjacent tiles: 9, E, J, O, T, Y, 15, and 19.
• Tile N has eight adjacent tiles: I, O, S, and five tiles within the sub-grid marked ?.
The rules about bugs living and dying are the same as before.
For example, consider the same initial state as above:
....#
#..#.
#.?##
..#..
#....
The center tile is drawn as ? to indicate the next recursive grid. Call this level 0; the grid within this one is level 1,
and the grid that contains this one is level -1. Then, after ten minutes, the grid at each level would look like this:
Depth -5:
..#..
.#.#.
..?.#
.#.#.
..#..
Depth -4:
...#.
...##
..?..
...##
...#.
Depth -3:
#.#..
.#...
..?..
.#...
#.#..
Depth -2:
.#.##
....#
..?.#
...##
.###.
Depth -1:
#..##
...##
..?..
...#.
.####
Depth 0:
.#...
.#.##
.#?..
.....
.....
Depth 1:
.##..
#..##
..?.#
##.##
#####
Depth 2:
###..
##.#.
#.?..
.#.##
#.#..
Depth 3:
..###
.....
#.?..
#....
#...#
Depth 4:
.###.
#..#.
#.?..
##.#.
.....
Depth 5:
####.
#..#.
#.?#.
####.
.....
In this example, after 10 minutes, a total of 99 bugs are present.
Starting with your scan, how many bugs are present after 200 minutes?
Your puzzle answer was 1921.
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.
If you still want to see it, you can get your puzzle input.
References
Visible links
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. https://en.wikipedia.org/wiki/Eris_(dwarf_planet)
. https://www.nationalgeographic.org/thisday/sep9/worlds-first-computer-bug/
. https://adventofcode.com/2019/day/20
. https://adventofcode.com/2019
. https://adventofcode.com/2019/day/24/input

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Advent of Code
--- Day 25: Cryostasis ---
As you approach Santa's ship, your sensors report two important details:
First, that you might be too late: the internal temperature is -40 degrees.
Second, that one faint life signature is somewhere on the ship.
The airlock door is locked with a code; your best option is to send in a small droid to investigate the situation. You attach your ship to Santa's, break a small hole in the hull, and let the droid run in before you seal it up again. Before your ship starts
freezing, you detach your ship and set it to automatically stay within range of Santa's ship.
This droid can follow basic instructions and report on its surroundings; you can communicate with it through an Intcode program (your puzzle input) running on an ASCII-capable computer.
As the droid moves through its environment, it will describe what it encounters. When it says Command?, you can give it a single instruction terminated with a newline (ASCII code 10). Possible instructions are:
• Movement via north, south, east, or west.
• To take an item the droid sees in the environment, use the command take <name of item>. For example, if the droid reports seeing a red ball, you can pick it up with take red ball.
• To drop an item the droid is carrying, use the command drop <name of item>. For example, if the droid is carrying a green ball, you can drop it with drop green ball.
• To get a list of all of the items the droid is currently carrying, use the command inv (for "inventory").
Extra spaces or other characters aren't allowed - instructions must be provided precisely.
Santa's ship is a Reindeer-class starship; these ships use pressure-sensitive floors to determine the identity of droids and crew members. The standard configuration for these starships is for all droids to weigh exactly the same amount to make them easier
to detect. If you need to get past such a sensor, you might be able to reach the correct weight by carrying items from the environment.
Look around the ship and see if you can find the password for the main airlock.
Your puzzle answer was 285278336.
--- Part Two ---
As you move through the main airlock, the air inside the ship is already heating up to reasonable levels. Santa explains that he didn't notice you coming because he was just taking a quick nap. The ship wasn't frozen; he just had the thermostat set to
"North Pole".
You make your way over to the navigation console. It beeps. "Status: Stranded. Please supply measurements from 49 stars to recalibrate."
"49 stars? But the Elves told me you needed fifty--"
Santa just smiles and nods his head toward the window. There, in the distance, you can see the center of the Solar System: the Sun!
The navigation console beeps again.
If you like, you can [ [Align the Warp Drive again] ] .
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.
If you still want to see it, you can get your puzzle input.
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