I declare this the first “Advanced Topics Challenge”. The Winner is allowed to carry this beautiful trophy in his/her signature:


- He/She can either create the next ATC or name someone to do so.
- Challenges can be anything from riddles, puzzles, code golf etc. The challenge doesn't have to be related to Scratch, but it should target the average AT-Reader. I think, the challenge should be something involving logic and crown a winner by objective means. However, the winner of a challenge has total freedom on the rules of it.
- Each challenge has a maximum time frame of one month (shorter time frames are advised).
- If the winner is decided by the first correct submission, then it would be fair to announce the challenge in advance, e.g. 24h before, in the thread of the previous challenge


I'll leave these here for quick access on upcoming challenges (thanks to PullJosh)






ATC#1:
Update: PullJosh solved the puzzle. Congratulations!

Make a Rule 110 program, that tells you, when a certain pattern appears first. This is simple, but the rules make it a bit tricky:
EDIT: Changed in “5.” “operators” to “blocks”.
You are now allowed to brainstorm in this thread, even if it spoils part of the challenge.

Explanation:
1. The character “X” corresponds to 1, the character “_” corresponds to 0.
2. The program only must be able to search for patterns starting and ending with X.
3. Line 1 corresponds to the input.
4. No system-variables means, you cant use any of the blocks, that have a checkbox left of them in the blocks menu.
EDIT:

([volume v] of [Stage  v])

isn't allowed either (it accesses built in variables).
5. No boolean operators means, you can't use any of the blocks that have 6 corners. Combining rules 5 & 6 means, that you also can't use the “if”, “if/else”, “wait until” and “repeat until” blocks.
6. No hacking means, that you have to be able to recreate that program in the original scratch editor, without importing or using blocks from the backpack.


The following table can help you to test your program (testname, input pattern, search pattern, expected output):

Oh, I see how one might do this without Booleans. I'll work on this later

Is the

([ v] of [  v])

block allowed to access variables? It doesn't have a checkbox next to it

joefarebrother wrote:

Is the

([ v] of [  v])

block allowed to access variables? It doesn't have a checkbox next to it

smart

joefarebrother wrote:

Is the

([ v] of [  v])

block allowed to access variables? It doesn't have a checkbox next to it

Oh, forgot about this one. Nope, this block isn't allowed either (it accesses built in variables). I will edit the rule explanation to make this clear.

Very.

Just to be clear: This is a puzzle for coders, not for lawyers. The goal is not to find legal loop holes, but to program with a limited selection of blocks.
And to avoid the question: A parameter (for example of a custom block) is NOT a variable, and therefore allowed.

Me thinking out loud: <spoiler>Tail-calling on broadcasts to simulate conditionals, and recursion to iterate through a string</spoiler>

MartinBraendli2 wrote:

Just to be clear: This is a puzzle for coders, not for lawyers. The goal is not to find legal loop holes, but to program with a limited selection of blocks.
And to avoid the question: A parameter (for example of a custom block) is NOT a variable, and therefore allowed.

The rules are the ones in described first, the explanation is just there for clarification. So if you manage somehow that the

<[5] > [2 ]>

block doesn't have 6 corners anymore, its still not allowed (Rules > Explanation). Its still a boolean operator, even without 6 corners.

EDIT: Nevermind

jokebookservice1 wrote:

Me thinking out loud: <spoiler>Tail-calling on broadcasts to simulate conditionals, and recursion to iterate through a string</spoiler>

<spoiler>
I don't see how broadcasts could be of any use. I only use them to create different “theads” or to “communicate” with other sprites
</spoiler>

MartinBraendli2 wrote:

jokebookservice1 wrote:

Me thinking out loud: <spoiler>Tail-calling on broadcasts to simulate conditionals, and recursion to iterate through a string</spoiler>

<spoiler>
I don't see how broadcasts could be of any use. I only use them to create different “theads” or to “communicate” with other sprites
</spoiler>

<spoiler>

broadcast(letter something of answer)

when I recieve X
do stuff

when I recieve _
do stuff

</spoiler>
EDIT: Forgot the closing HTML spoiler tag

Is anyone trying to solve this?

I'll try.
How are edges handled?

BookOwl wrote:

I'll try.
How are edges handled?

What do you mean by “edges”? The program must be able to (theoretically) handle rows of infinite width, so you cant put a limit on that (for example limiting your program to 100 cells per row).
Or do you mean something different?

I meant how do I handle the first and last cells?

Every row starts and ends with X, so on the next row, you always start with r(__X), which is an additional X, and end with either r(XX_) or r(_X_), which both gets X. You don't need to go further, because r(X__) will give you _.

So if you start with X (or 1), you get

I declare this the first “Advanced Topics Challenge” (Original post got updated). I hope this catches on, there are currently too many challenges at once (IMO)

MartinBraendli2 wrote:

I declare this the first “Advanced Topics Challenge” (Original post got updated). I hope this catches on, there are currently too many challenges at once (IMO)

There are already lots of AT challenges, so Im not sure if you can call it the first.

I have an idea in terms of recursion to emulate variables, but that's just going to explode the stack, as Scratch isn't tail call optimised