Advent of Code 2022 journey

As I did last year, I decided do AOC this year. I feel it is a bit harder than last year. This is just the journey of 2022 AOC. All code host on here

Day 1-6

The logic is pretty straight forward. Just parse the input and write logic plainly in code.

Day 7

After transitional warming up for 6 days, it becomes a bit more interesting in day 7. Day 7 is the tree problem. Different from days before, plain writing wasn’t the best way. (Even I write it in the plain way).

I use recursive and keep a hash table for recording of file/dir size. It works, but I think use a tree structure must be better solution.

Day 8 & 9

Day 8 logic is pretty easy just need a write bunch of code. Day 9 take me a while. I was using a stack for keep the status of directions of nodes of the line. However, I don’t need it. There is a general way to move close to head. After use that, only thing tricky is day9 part2’ head-to-tail movement.

Day 10

Part 2 of day 10 is pretty fun. Check index every loop and go find if the index located inside the sprite (be calculated by part1 logic). And print letters eventually. I just like the print letter design.

Day 11

It is easy to implement day 11 if the language can use lambda. I let each monkey become a list that contained all items, the operation (lambda), and the test (lambda). Then, the solution is straight forward.

Day 12

I write the recursive function at beginning and the status are complex because I used hash-table as record. In common lisp, get the value of hash-table can give the nil (None), and I have to make sure the value after I check if it is nil (None) or not. Just very tricky. So I use another way, an queue, to do day 12.

Day 13

Day 13 part1 is my favorite. The data input format is so lispy.

(defun replace-input (input)
   "," " "
	"]" ")"
	(str:replace-all "[" "(" input))))

(defun read-one-input (input)
  (read-from-string input))

Just the code upper, can change the data input to lisp code. Then I need a compare function to compare the value depends on the type (integer, cons, etc.)

I don’t like the part2 because it is too inconsistent. It is easy to get the answer by just using the “sort by” which implemented by a lot languages nowadays. But it means if someone don’t know how to use it, and want to brute force all positions. There are a lot options that can be used to insert.

Day 14

Day 14 is fun. Not tricky, just fun.

Day 15

Day 15 logic is

  1. find the closest B with S
  2. get the Manhattan distance from B to S
  3. draw the map.

The tricky part is part2. I need to find the empty point inside the map. So I loop all row and col and the S-B pair to find the empty point. The Big O is row * col * S-B pairs. It takes a long time. And I find in each row, if I find one point’s related S-B, and I can just jump forward depends on the distance from S and B. And after this tiny change. the result appears. Not very fast, but fast enough.

I learned something from the part2, The Big O actually doesn’t change, just optimize a bit in each loop can also give a big improvement.

Day 16

I failed.

Day 17

Day 17, I change language from common lisp to Rust. Day 17 is hard, and several tricks inside.

First trick, it is Tetris. Second trick, every line is 7 spots, which means if they are bits, a full line is 1111111.

Then the first part has a easy way to determine if this Rock can keep going down or not. When rock reach the old rocks (after 4 steps), put the highest line into the buffer, and compare the buffer with the rock line to line. Each line does !(a | b == a + b), if it is true, means this rock cannot reach this deep. Then rock go back one step, and stop there, and update the results.

Part 2 looks like hard but actually I noticed the trick when I saw it. It repeats. Means if I split the rock tower with the fulled line (1111111), it is going to repeat the height from last fulled line to the next one like x, a, b, c, d, a, b, c, d, etc. So do the rocks number. So I need minus the first rock number of height x, and divide the (a_rocknum + b_rocknum + c_rocknum + d_rocknum) to get the repeat time. Then module the rocks number to get the real very small input. The get the height of the input and add the x + (a + b + c + d) * repeat.

Day 18

Part 2 is tricky. Has to use algorithm Flood fill

Day 19

Recursive recursive and recursive.

Day 20

I write day 20 in lisp at beginning, but with the circle list. Find the next number which should be move. It looks good but I forget there might be duplicated numbers. So each number should has flag shows if this number has moved or not.

Day 21

Day 21 part 1, I use a hash table keep each expression, and keep looping the hash table until all values are number.

Then part 2 cannot use this brute force, I tried to guess the number but it runs forever. So, the solution is: root node has two arguments, one of it we already know. I just need to reverse back from the root to humn node.

More interesting is I write part 2 with a lisp parser. Each key can be a lisp expression then reverse back and get the answer isn’t that hard. Further more, I re-write part 1 with this solution and get the part 1 result just a eval in lisp.

Day 22

A lot code in part 1, and when I saw the part 2, I give up.

Day 23

The hardest part is understanding the meaning of puzzle.

Day 24 & 25

I give up.


I give up right before the end. What a pity. However, I think I will join the next years AOC again for fun. I have several thoughts about AOC this year.

  1. I think some game developers make puzzles of 2022. For example, day22 part2 3D map moving; day 18 part2, 3D surface detection. Just too obviously to use in the game developing. And day17, Tetris.
  2. Some algorithm appear often in this year’s solutions. BFS/DFS/Dijkstra/etc. straight forward brute force solution cannot solve all puzzles.
  3. Even tiny optimization can lead to the huge improvement. Even the Big O doesn’t change.
Written on December 25, 2022