feecIe6418's blog

By feecIe6418, 20 months ago,

Hello Codeforces!

On Jun/25/2022 17:35 (Moscow time) we will hold Codeforces Global Round 21.

It is the third round of a 2022 series of Codeforces Global Rounds. The rounds are open and rated for everybody.

The prizes for this round:

• 30 best participants get a t-shirt.
• 20 t-shirts are randomly distributed among those with ranks between 31 and 500, inclusive.

The prizes for the 6-round series in 2022:

• In each round top-100 participants get points according to the table.
• The final result for each participant is equal to the sum of points he gets in the four rounds he placed the highest.
• The best 20 participants over all series get sweatshirts and place certificates.

Thanks to XTX, which in 2022 supported the global rounds initiative!

All problems except one are authored and prepared by me. The other problem is authored by gyh20.

We would also like to thank the following people:

Round information:

• duration: 2 hours and 15 minutes
• number of problems: 8
• score distribution: 500-1000-1500-2000-2000-2500-3250-4000

We are looking forward to your participation!

Upd Editorial https://codeforces.com/blog/entry/103479

Upd Winners!

Announcement of Codeforces Global Round 21
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By feecIe6418, 21 month(s) ago,

Thanks for participation!

If your solution to D involves any data structures and is not $O(n)$ -- please read the "solution 1". I believe it is very interesting, but to make the difficulty suitable for D we allowed not $O(n)$ solutions.

1696A - NIT orz!

Hint 1
Solution

1696B - NIT Destroys the Universe

Hint 1
Hint 2
Solution

1696C - Fishingprince Plays With Array

Hint 1
Hint 2
Solution

1696D - Permutation Graph

This problem has two different solutions. The first one is more beautiful, but less straight-forward.

Hint 1 for solution 1
Hint 2 for solution 1
Hint 3 for solution 1
Solution 1
Hint 1 for solution 2
Hint 2 for solution 2
Solution 2

1696E - Placing Jinas

Hint 1
Hint 2
Hint 3
Solution

1696F - Tree Recovery

Hint 1
Hint 2
Solution

1696G - Fishingprince Plays With Array Again

Hint 1
Hint 2
Hint 3
Solution

1696H - Maximum Product?

Hint 1
Hint 2
Solution
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By feecIe6418, 3 years ago,
A Tutorial
A Code
B Hint 1
B Hint 2
B Hint 3
B Tutorial
B Code (Python)
C Hint 1
C Hint 2
C Tutorial
C Code
D Hint
D Tutorial
D Code (Python)
E1 Hint
E1 Tutorial
E1 Code
E2 Hint
E2 Tutorial
E2 Code
• +184

By feecIe6418, history, 3 years ago,

I was trying to hack myself in D. It got hacked successfully, but when I resubmitted it, it still passes in 982ms. I was trying to generate a better test so that it definitely couldn't pass.

So I generated another test, and tried to hack, but the system return "Unexpected verdict". Do that mean the system is not working? Or the authors' solution is wrong? Or something else?

I told my friend tianxiawoyou and when he hacks me, the verdict is still "Unexpected verdict". I tried to hack another person, but it seems that the system is working.

Here is my generator (I tried both uploading the generator and the file, but both returns "Unexpected verdict")

code
• +32

By feecIe6418, history, 3 years ago,

Hello Codeforces!

gyh20 and I are glad to invite you to Codeforces Round 670 (Div. 2) which will start on 12.09.2020 16:45 (Московское время). Note the unusual start time of the round.

The contest will last for two hours, and you will have five tasks to solve. The tasks are prepared by me and gyh20. This round is rated for participants whose rating is not higher than 2099. You can see that my current rating is exactly 2099 :)

There might be an interactive problem. You can learn about them here.

We would like to thank:

We tried our best to make the statements short and clear, pretests strong and problems interesting. We hope you like the problems!

Score distribution will be announced shortly before the round.

Good luck and have fun!

Upd: Score distribution is 500-750-1250-1750-2500.

Upd: For problem reasons, the contest is delayed for 10 minutes. We are very sorry to keep you waiting, sorry again.

Upd: Score distribution is changed to 500-1000-1500-2000-2750.

Upd: The round is finished. We're really sorry for B being well-known (none of the testers knew the harder version of this problem in ABC173E). Still, congratulations to the winners!

Div1 (unofficial):

Div2:

Upd: Editorial is out here.

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