Hello CodeForces Community,

We are happy to invite you to participate in Winter Cup 6.0 Online Mirror Contest. The mirror is scheduled to take place on Codeforces at [contest_time:479486] and will last for 5 hours.

Winter Cup is a prestigious annual competitive programming contest held by ACM, INSAT Student Chapter. It unites Tunisia's brightest minds in a thrilling display of skill and innovation. Widely regarded as the nation's best competition, aside from the official ICPC regional contest.

The contest consists of 15 problems created and prepared by Iceberg, OussamaJB and ramizouari with difficulties from div2A to div1D.

We would like to thank :

The organization team for preparing logistics, and the SysAdmins for configuring and testing the Judging System.

Mtaylor, SMIrrichto, ElyesChaabouni, khalil__, GH1hatem, LorenzoRaed02 for testing the round and providing valuable advice.

MikeMirzayanov for Codeforces and Polygon platforms.

Enjoy solving !

You can find here links to Winter Cup 4 and Winter Cup 5

**UPD** : Editorial

Good Luck in the Contest !

[deleted]

Good luck to the participants, I hope you enjoy the problemset !

Good Luck Guys. Hope you enjoy the problemset. Give us your feedback later!

As a tester I really enjoyed this year problemset! GJ guys!

Good luck to the participants ! As a tester I enjoyed the problems!

Is there any editorial?

The editorial is out. Check the link in the post.

I feel no. of participants in round do not justify the problem quality. Every problem had something unique and interesting.

Thanks to the authors really enjoyed the Problemset. Kudos.

CAn you share your approach for problem F find the tree?

This problem requires observation, Try to build a tree with some property and you will get the answer.

First we have to take care of $$$v_i = i$$$ then we cannot construct tree.

Now if our $$$ N = 2$$$ we will always have a tree. Given in sample case.

For $$$ N > 2 $$$ if we have all nodes from $$$1, 2, ..., N$$$ in the $$$v$$$ array, tree cannot be formed. Because we cannot have all the nodes which are leaves.

Now consider if a node is not present in the tree, you will always construct a Star Tree with this node in centre. So answer is Yes.

Thank you for your comment, we were really happy reading your feedback. I also wanted to say that we just released the editorial.

Excited for Winter Cup 6.0. A prestigious event showcasing Tunisia's top talent in competitive programming.

Any hints for L2

if we find an index $$$j$$$ such that $$$a_j$$$ is a prime > $$$n/2$$$

then for each $$$i \neq j$$$ ;$$$ \ lcm(a_i , a_j) = a_i \cdot a_j $$$ ; (so we can guess the whole array)

because $$$a_i$$$ can't be equal to $$$a_j \cdot q$$$ where $$$q > 1$$$ otherwise it will exceed $$$n/2$$$.

And we have $$$ m \approx \frac{n}{ln(n)} - \frac{\frac{n}{2}}{ln(\frac{n}{2})} $$$ primes > $$$n/2$$$

$$$m/n > 1/30$$$ so we can use randomization.

try 100 indices and check if one of them is prime $$$> n/2$$$

and then we can guess the whole array.

Thanks, I missed randomization idea.

errichto's video

I have seen this But never solve a problem which uses randomization idea Can you elaborate this question a bit more, it builds analogy for me like where and how to check if randomization work or not