As I did last year, I’m going to solve the Advent of Code problems again this year.
Or that was the plan. It turns out that instead I put down my blog for almost a year and a half and never quite got around to doing these problems. So I’m actually backdating these posts from the early days of 2018 to where they would have been had I solved them on time. They’re still interesting problems, so give them a read.
Part 1: Take the assembunny interpreter from day 12 and add one new instruction (out
x) which transmits the valuex(either an integer or register). Find the lowest value we can initializeato so that theoutput signals form an infinite repeating pattern of0,1,0,1, …
Part 1: Given a map of the form:
########### #0.1…..2# #.#######.# #4…….3# ###########
> Find the shortest route to visit each of the points, starting at `0`.
First, we want to take the map that we were given and simplify it. We know that we want to visit all of the points, so lets take the original map and turn it just into a map of distances between any two named points.
```python
walls = set()
name_to_point = {}
point_to_name = {}
# Load the input file into a set of walls and the location of points of interest
for y, line in enumerate(fileinput.input(args.files)):
for x, c in enumerate(line.strip()):
if c.isdigit():
name_to_point[int(c)] = (x, y)
point_to_name[(x, y)] = int(c)
elif c == '#':
walls.add((x, y))
# Dynamically fill a distance map to a given point
def distances_to(name):
to_scan = queue.Queue()
to_scan.put((name_to_point[name], 0))
scanned = set()
result = {}
while not to_scan.empty():
point, distance = to_scan.get()
if point in point_to_name:
name = point_to_name[point]
if name not in result:
result[name] = distance
if point in scanned:
continue
else:
scanned.add(point)
x, y = point
for xd, yd in [(-1, 0), (1, 0), (0, -1), (0, 1)]:
neighbor = (x + xd, y + yd)
if neighbor not in walls:
to_scan.put((neighbor, distance + 1))
return result
distances = {
name: distances_to(name)
for name in name_to_point
}
names = list(sorted(name_to_point.keys()))
The first part loads the map and the second part will flood fill out from each point. This will find the minimum distance from each named point to the given one, somewhat simplifying the problem.
Part 1: Take the assembunny interpreter from day 12 and add an instruction (tgl
X) that modifies the code at an offset ofXinstructions.
incbecomesdec; any other one argument instruction (includingtgl) becomesincjnzbecomescpy; any other two argument instructions becomejnz- Toggling an instruction outside of the program does nothing (it does not halt execution)
- If toggling produces an invalid instruction, ignore it
Run the given program with the initial register of
a = 7. What is the final value in registera?
Part 1: You are given a grid of nodes and the output of the df command telling you how much space is on each. How many pairs of nodes are there where the data from some node
Awould fit entirely onB?
Part 1: Another virtual machine, of sorts. Start with the string
abcdefghand apply a sequence of the following commands to it:
- swap position
Xwith positionY= swap two positions- swap letter
Xwith letterY= swap to letters, no matter where they are- rotate (left|right)
Xsteps = rotate forward or backward- rotate based on position of letter
X= findX, rotate right based on its position; if the original position was >= 4, rotate one more1- reverse positions
XthroughY= reverse a subset of the string- move position
Xto positionY= take a character at a position out of the string and put it somewhere else specific
Part 1: Given a list of integer ranges (a la
5-8), what is the first value not in any given range?
Part 1: Create a circular list of the numbers
1throughn. Going around the list, each currently remaining number removes the number after it. What is the last remaining number?
Part 1: Starting with a sequence of
.and^, generate additional rows using the rules based on the three characters above the new position.
^^.->^.^^->^^..->^..^->^- Otherwise ->
.
How many safe tiles (
.) are there after 40 generations?
Part 1: Create a 4x4 grid of rooms with doors
Up,Down,Left, andRight from each location. To determine if a door is currently open:
- Calculate
MD5(salt + sequence)where sequence is a string containing any combination ofUDLRdepending on how you got to this room- The first four hex values represent the doors
Up,Down,Left, andRight respectively:bcdefmeans open; anything else is closed
Find the shortest path from
(0, 0)to(3, 3).