Hello Codeforces!

I organized a contest at my university in November 2023, and I'm happy to welcome all of you to participate virtually or solve the problems later on.

**Contest link**: Intra Department Programming Contest, CSE-BU

There are **8 problems** and **150 minutes** to solve them. **Problems are not sorted by difficulty order. I recommend you to read all the problems.**

This problemset were create for users with a rating range from 0 to 1400 but anyone welcome to participate virtually or upsolve the problems!

I would like to thank everyone who was involved in the contest preparation:

- Rudro25, AmiNuL72 for testing the problems and providing useful feedback.
**You**for participating.- MikeMirzayanov for Polygon and Codeforces platforms.

I tried my best to keep the statements short and clear and I hope you will like the problemset!

Happy Coding!

what's wrong with this

F WA 6I used the exact same code but, for prefix, used an array instead of vector. Got AC.

CodeThanks! can you explain why using vector gives WA

It's actually not your fault. Constraints clearly show that 1 ≤ l, but test 6 actually has l less than 1. I tried using using .at() function instead of [] and got runtime error, while using pref[max(l — 1, 0)] passed.

Thank you so much!

forIoop Thanks for your help. I've sorted out the constraints and test cases, so everything should be fine now.

alpha1215 You have to consider the case when

L=0.Unfortunately I missed the constraints

(0 $$$\le$$$ L). Now I fixed it and everything alright.Nice contest, though I do feel it's still easier than regular Div.4.

Thoughts and feedbacks from an outsiderThe contest feels a bit math-heavy. I do feel like it could have covered a few more algorithmic topics than this, E is a bit unnecessary (I meant, I might be in the dark, but who are the participants of this contest to have a HelloWorld-like problem? If they are freshmen, then sure, it's acceptable), but overall the maths weren't so bad.

Speaking of E, I was kinda confused at first as the statements and the outputs didn't really linked together. The backstory seemed to imply us to try spelling

`Exactly`

, while the actual output is a different story.Problem constraints seemed a bit inconsistent. B could have had $$$n \le 2 \cdot 10^5$$$ without harming the intended solution. And why did D have $$$n \le 10^6$$$? I don't get the idea of what you're trying to block with this constraints, but AFAIK, the most braindead solution for D is a very high coefficient STL-based $$$\mathcal{O}(n \log n)$$$ — and it still worked just fine here. It could have been $$$2 \cdot 10^5$$$ and thus removing the hassle of fastio.

Problem statements could have made use of LaTeX more. I think the writer just learnt it recently, and could only apply it sparsely and yet without a regulation of when to use those. It's alright, it didn't harm the overall readability, but I hope they could do better next time.

The rest is standard educational stuff, so I don't have much to comment.

At any rate, I really appreciated these contents, regardless of how basic they are. After all, newbies tend to need those building blocks the most.

UPD:Edited recommended constraints to $$$2 \cdot 10^5$$$ because sometimes weird pragmas actually pushed $$$\mathcal{O}(n^2)$$$ bruteforce past 1s TL if $$$n \le 10^5$$$ only.AkiLotus Thanks a lot for your valuable suggestions.

Good Initiative.

Thank you for setting this up, it was fun to do.

My short feedback would beto pay a little bit more attention to making the problem statements clearer. For instance when I first read F, I thought that we are looking for numbers that are sums of three different primes, like 2+3+5 for instance. Also in problem G the third rule should have been "The absolute difference between

number oftasks of consecutive two days is one".Other than that I feel the problem set was varied enough in difficulty and style for the intended audience.

SleepyOverlord Thanks for your feedback.

why in C just sorting and returning square of min of 4 max elements gives WA on test 15