One of the many reasons why SAPO is the best informatics Olympiad is that we're allowed to submit solutions in Scratch (TianCilliers wrote a CMS plugin to support Scratch a while ago)

The second round of SAPO 2020 was held earlier this week, so obviously I had to try to solve the problems using Scratch.

The problems were:

• Given X, Y, and N, output N / X + N / Y - N / lcm(X, Y).
• Add two given numbers in base B for a given B.
• This problem but modulo 1e8.
• Given a tree and some paths, find the number of edges in the union of those paths.

I was able to solve the first and third problems this way:

but I couldn't implement the second and fourth problems.

As you can see in the code for problem 3, working with multiple arrays is a bit of a nightmare.

I feel like problem 2 is solvable using Scratch (albeit very painfully), but since Scratch doesn't have 2D arrays, I don't see how one could solve problem 4 using Scratch.

Do any of you have ideas about how one can work with graphs using Scratch?

(P.S. my other Scratch implementations are available at https://github.com/dolphingarlic/ScrAtChO)

EDIT: Thanks to -is-this-fft-, I was able to implement a solution for problem 4. https://scratch.mit.edu/projects/419364160