antontrygubO_o's blog

What were your favorite problems in 2021?
By antontrygubO_o, 3 years ago, In English

As the last big contest of 2021 is over, I think it's time.

It seems that there were just more and more ad-hocs/"deeply analyze some complicated process" everywhere... But maybe you still liked something.

So, what were your favorite problems in 2021?

  • Vote: I like it
  • +386
  • Vote: I do not like it

Comments Comments (39)
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3 years ago, # |
  Vote: I like it +48 Vote: I do not like it

1583F - Defender of Childhood Dreams

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3 years ago, # |
  Vote: I like it +1 Vote: I do not like it

hmm, 2021 was full of interesting tasks, so I even can't enumerate them, but these problems I remembered the most:

I hope somebody will enjoy them as well as I did.

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3 years ago, # |
  Vote: I like it -32 Vote: I do not like it

Last round's problem B :)

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3 years ago, # |
  Vote: I like it +30 Vote: I do not like it

Codechef: Max-Min Rotations from November Lunchtime https://www.codechef.com/LTIME102A/problems/MNMXROT

Atcoder: Set merging from AGC055 https://atcoder.jp/contests/agc055/tasks/agc055_e

Codeforces: I loved Global Round 15, especially F and G were really enjoyable.

Honorable mention from other competitions: ICPC WF problem about snowblowers. Most people will think it's garbage, but I've actually enjoyed it a lot. There are at least two different clever ways to do it that are not painful.

https://open.kattis.com/problems/snoproblem

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3 years ago, # |
← Rev. 2   Vote: I like it +98 Vote: I do not like it

My favorite problems from Codeforces this year:

1491I - Правитель зоопарка by oolimry

1503F - Сбалансируйте карты by Monogon

1508D - Обмены на ребрах by Ari

1548E - Грегор и два маляра by Benq

1552G - Серьезный судья by cip999 and dario2994

1552H - Угадайте периметр by cip999 and dario2994

1553H - XOR и расстояния by 244mhq

1586F - Защитник детских мечт by MagentaCobra

1610H - Игра в кальмара by Tet and AliShahali1382

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3 years ago, # |
  Vote: I like it +60 Vote: I do not like it
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3 years ago, # |
  Vote: I like it +48 Vote: I do not like it

1586I - Omkar and Mosaic by rabaiBomkarBittalBang

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3 years ago, # |
  Vote: I like it +21 Vote: I do not like it

1537F - Figure Fixing

1589D - Guess the Permutation

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3 years ago, # |
← Rev. 2   Vote: I like it +98 Vote: I do not like it

Here is my favourite problems (July ~ Dec):

interesting problems

  • CF1622F Quadratic Set by Neon
  • CF1610F Mashtali: a Space Oddysey by AliShahali1382
  • CF1612F Armor and Weapons by BledDest
  • CF1605F PalindORme by ExplodingFreeze and antontrygubO_o
  • CF1586I Omkar and Mosaic by rabaiBomkarBittalBang
  • CF1592F2 Alice and Recoloring 2 by Bakry, Hemose and KostasKostil
  • CF1567F One-Four Overload by flamestorm
  • CF1562F Tubular Bells by Wind_Eagle
  • CF1548E Gregor and the Two Painters by Benq
  • CF1552H Guess the Perimeter by cip999 and dario2994
  • CF1553H XOR and distance by 244mhq
  • CF1545C AquaMoon and Permutations by AquaMoon
  • CF1545D AquaMoon and Wrong Coordinate by AquaMoon
  • CF1543E The Final Pursuit by JaySharma1048576

"trick" problems

educational problems:

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3 years ago, # |
  Vote: I like it +12 Vote: I do not like it

https://oj.uz/problem/view/APIO21_jumps

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3 years ago, # |
  Vote: I like it 0 Vote: I do not like it

any problem from AtCoder Regular Round

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3 years ago, # |
  Vote: I like it +35 Vote: I do not like it

The randomized solution of 1514D

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3 years ago, # |
  Vote: I like it -30 Vote: I do not like it

B. TMT Document by Ari

B. Divine Array by Anti-Light

B. Scenes From a Memory by Wind_Eagle

D. Diane by YouKn0wWho

D2. Too Many Impostors (hard version) by snowysecret

C. Baby Ehab Partitions Again by mohammedehab2002

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    3 years ago, # ^ |
      Vote: I like it +8 Vote: I do not like it

    Thank you! But did you even solve or look at the problems?

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3 years ago, # |
  Vote: I like it +5 Vote: I do not like it

Problem E from Bytedance-Moscow Workshops camp training contest 2. You had to write a randomised implementation of binary search, such that for each $$$i$$$, you need in expectation at most $$$log_2(n + 1) + 0.1$$$ queries to find $$$i$$$.

The problem is natural and interesting, and the intended solution is clean and beautiful. The problem might seem easy, but is in fact very hard (only 2 teams and none of the top 10 of the contest solved it!).

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3 years ago, # |
← Rev. 4   Vote: I like it +2 Vote: I do not like it

1583F - Defender of Childhood Dreams Like: Dislike:

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3 years ago, # |
← Rev. 2   Vote: I like it +54 Vote: I do not like it

Happy holidays Anton!

My favorite problems that you authored this year are:

Unfortunately, I don't fully understand the solutions to any of them (yet).

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3 years ago, # |
  Vote: I like it +39 Vote: I do not like it

AGC055E Set Merging by antontrygubO_o.

I am curious how can a human brain come up with such solutions ?

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3 years ago, # |
  Vote: I like it +10 Vote: I do not like it

My favorite problem from cf : https://oj.uz/problem/view/APIO21_roads

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3 years ago, # |
← Rev. 5   Vote: I like it -20 Vote: I do not like it

My favorite problems are 1549D, 1602D and YATP

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3 years ago, # |
← Rev. 4   Vote: I like it +4 Vote: I do not like it

Mine: 1593G — Changing Brackets.

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3 years ago, # |
  Vote: I like it +11 Vote: I do not like it

1503C - Travelling Salesman Problem

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3 years ago, # |
← Rev. 2   Vote: I like it +9 Vote: I do not like it
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3 years ago, # |
← Rev. 2   Vote: I like it 0 Vote: I do not like it

I didn't checked out a lot of problems this year, but I really liked these two problems:

I also really liked Sorter Prodigy, but it turns out to be the best problem of 2018.

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3 years ago, # |
← Rev. 4   Vote: I like it +9 Vote: I do not like it

1900:

2000:

2100:

2200:

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3 years ago, # |
  Vote: I like it +63 Vote: I do not like it

My favorite problems in 2021:

  • Final Exam, from Petrozavodsk Winter 2021 PKU Contest
  • Rectangle Painting, from Petrozavodsk Winter 2021 NNSU Contest (XXI Open Cup GP of Nizhny Novogorod)
  • Build The String, from XXI Open Cup GP of Urals
  • Slide Circuits from Google Code Jam 2021
  • Joy with Permutations, from Petrozavodsk Summer 2021 Kyoto U Contest (KCPC 2020)
  • K-onstruction, from Petrozavodsk Summer 2021(XXII Open Cup GP of IMO)
  • Pac-Man Speedrun from RuCode 4.0 Championship
  • Interesting Numbers from AMPPZ 2021 (MW Day 1, XXII Open Cup GP of Poland)
  • Short Coding from ICPC Yokohama Regional 2020 (in 2021)
  • Squid Game from ICPC Seoul Regional 2021
  • 1%-Euclidean from ICPC Moscow Regional 2021
  • Areny from Potyczki Algorytmiczne 2021, Runda 4
  • Drzewo czerwono-czarne from Potyczki Algorytmiczne 2021, Runda 5
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    3 years ago, # ^ |
      Vote: I like it +24 Vote: I do not like it

    I'm glad to hear that, but remember that the problems from Potyczki Algorytmiczne are usually used to create Open Cup rounds, so if anybody is curious about the mentioned problems -- it's best to wait.

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3 years ago, # |
  Vote: I like it +23 Vote: I do not like it

Paired Up by Benq

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3 years ago, # |
← Rev. 2   Vote: I like it 0 Vote: I do not like it

https://mirror.codeforces.com/contest/1551/problem/E by MikeMirzayanov. I really liked this problem, learnt something new

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3 years ago, # |
← Rev. 3   Vote: I like it 0 Vote: I do not like it
1600
1700
1800
1900
2000
2100
2200
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3 years ago, # |
← Rev. 2   Vote: I like it +14 Vote: I do not like it
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3 years ago, # |
  Vote: I like it +10 Vote: I do not like it

1583F - Defender of Childhood Dreams

1542B - Plus and Multiply

1534F2 - Falling Sand (Hard Version)

ARC121D — 1 or 2

AGC056C — 01 Balanced

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3 years ago, # |
← Rev. 2   Vote: I like it +54 Vote: I do not like it

Here are some of my favorite problems in chronological order of their corresponding contests and the reasons I like them:

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3 years ago, # |
← Rev. 2   Vote: I like it +5 Vote: I do not like it

From AGC :

(all from antontrygubO_o)

From Codeforces:

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3 years ago, # |
  Vote: I like it +5 Vote: I do not like it

i find this problem extremely beautiful , i remember sweet struggling for few days on it .

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3 years ago, # |
  Vote: I like it 0 Vote: I do not like it

I am in process of solving New Year problems and if I have to nominate one problem from these it's definitely 41. Kingdoms and Quarantine (originally from some Summer Petrozavodsk contest). It's really great

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