Thank you for participation! Here is the editorial:
1621A - Stable Arrangement of Rooks
1621G - Weighted Increasing Subsequences
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Thank you for participation! Here is the editorial:
1621A - Stable Arrangement of Rooks
1621G - Weighted Increasing Subsequences
Hi, Codeforces! Happy New Year!
I'm glad to invite you to Hello 2022, which will take place on Jan/03/2022 17:35 (Moscow time). You will have $$$2$$$ hours $$$15$$$ minutes to solve the problems. This round is rated for everyone.
All problems are authored by me. I would like to thank 74TrAkToR for excellent round coordination and MikeMirzayanov for great Codeforces and Polygon.
There can be an interactive problem in this round. Don't forget to read the guide on interactive problems.
The scoring is $$$500-1000-1500-1750-2250-2750-3000-3500-4500$$$.
Good luck!
Thank you for participation! Congratulations to the winners:
Thank you for participating in the contest! I hope you enjoyed the tasks. Here is an editorial with hints.
1474A - Puzzle From the Future
Hint $$$1$$$: Should we always make first digit of $$$d$$$ not equal to $$$0$$$? How can we do it?
Hint $$$2$$$: Try to choose such $$$a$$$ that $$$d$$$ will have $$$n$$$ digits.
Hint $$$1$$$: Integer have exactly $$$4$$$ divisors, if it is of form $$$pq$$$ or $$$p^3$$$ for some primes $$$p$$$ and $$$q$$$. In the first case it have divisors $$$1$$$, $$$p$$$, $$$q$$$, $$$pq$$$. In the second case it have divisors $$$1$$$, $$$p$$$, $$$p^2$$$, $$$p^3$$$.
Hint $$$2$$$: Instead of finding integer with at least $$$4$$$ divisors, find integer with exactly $$$4$$$ divisors.
Hint $$$3$$$: Let $$$p$$$ be the smallest prime factor of $$$a$$$. Then, $$$p \geq d + 1$$$.
Hint $$$1$$$: How does $$$x$$$ changes after each operation?
Hint $$$2$$$: Suppose, that you know $$$x$$$. What pairs of elements can you throw out now?
Hint $$$3$$$: Suppose, that you did some operations. Note, that if you have integer $$$b$$$ that is greater or equal to $$$x$$$ and $$$b$$$ is still in array $$$a$$$, you can't remove $$$b$$$ from $$$a$$$, thus you can't throw out all elements of $$$a$$$.
Hint $$$4$$$: You don't know $$$x$$$ only before the first operation and $$$n \leq 1000$$$.
Hint $$$1$$$: How to solve the promblem if we are not allowed to use a superabilty (in linear time)?
Hint $$$2$$$: Look at the first pile. There is only one way to remove stone from the first pile.
Hint $$$3$$$: If you swap $$$i$$$-th and $$$(i + 1)$$$-th piles of stones, nothing changes in way you remove stones from $$$1$$$-st, $$$2$$$-nd, $$$\ldots$$$, $$$(i - 2)$$$-th piles.
Hint $$$4$$$: Look at the problem from the both sides: from the beginning of $$$a$$$ and from the end of $$$a$$$.
Hint $$$1$$$: How many operations will robot make in the worst case?
Hint $$$2$$$: How many times can robot spend $$$(n - 1)^2$$$ time on $$$1$$$ operation?
Hint $$$3$$$: How many times can robot spend $$$(n - 2)^2$$$ time on $$$1$$$ operation? It is easyer to think about number of operations with time greater or equal to $$$(n - 2)^2$$$.
Hint $$$4$$$: Instead of operation from the statement we can apply the following operation to $$$q$$$ which is initially an identity permutation:
Then we make $$$p$$$ = $$$q$$$ and do operations in reversed order.
Can you solve this problem with a bigger $$$n$$$?
Good luck in your future contests!
Hi, Codeforces!
I'm glad to invite you to take part in Codeforces Round #696, which will take place on Jan/19/2021 17:35 (Moscow time). Round will be rated for participants with rating less than $$$2100$$$. Participants from the first division can take part out of competition.
There will be $$$6$$$ problems for $$$2$$$ hours. All problems are authored by me. Thanks to adedalic for excellent round coordination and to MikeMirzayanov for Codeforces and Polygon.
Also thanks to testers errorgorn, awoo, kalki411, RetiredPlayer, AmShZ, IaMaNanBord, Osama_Alkhodairy, Prakash11, Gauravvv, HIS_GRACE, Dragnoid99 for testing the round and giving valuable feedback for problems.
Scoring is $$$500-1000-1500-2000-2250-3000$$$.
Good luck!
UPD: Editorial
UPD: Congratulations to the winners!
Of both divisions:
Of the second division:
Hello Codeforces!
Now the winter SIS (Summer Informatics School) is taking place, and parallel A+A0 and its teachers have prepared a complete Codeforces Round. You can check previous rounds, prepared by SIS students: Codeforces Round #612, Codeforces Round #530.
Codeforces Round #694 begins on Jan/05/2021 17:35 (Moscow time). In both redactions, there will be $$$6$$$ problems for $$$2$$$ hours. The round is rated for both divisions.
Problems are authored and prepared by AliceG, pakhomovee, MadProgrammer, ArtNext, fastmath, IgorI, Kapt, KhB, Hello_zoka, Karabutsa, ligaydima, Mangooste, pelmenner, daubi under the guidance of meshanya, cdkrot, kokokostya, craborac, scanhex.
We would like to thank:
300iq for round coordination.
MikeMirzayanov for Polygon and Codeforces.
LHiC, budalnik, KAN, Monogon, IaMaNanBord, ld_minh4354, Gauravvv, Vergara for testing the round and giving useful feedback.
We recommend you to read the statements of all problems. Scoring will be announced later.
Good luck!
Scoring distribution is: $$$500 - 750 - 1000 - 1500 - 2000 - 2500$$$ in both divisions.
System testing is over. Thank you for participating! We hope that you liked our problems!
Congratulations to the winners:
All of them have solved problem E (with neal being the first). Problem F was quite challenging and no one have solved it during the contest.
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