antontrygubO_o's blog

[CONTEST OVER] MIT Informatics Tournament 2024 Spring Invitational
By antontrygubO_o, 8 months ago, In English

Update 2: The Qualification Round has officially concluded! A huge thank you to our contestants for joining us and supporting this new initiative! Congratulations to the top 16 finalists who are advancing to the finals round (along with many more as we continue to confirm people's availability)!

  1. Rewinding
  2. ksun48
  3. Petr
  4. Geothermal
  5. mango_lassi
  6. hank55663
  7. ecnerwala
  8. jqdai0815
  9. Kevin114514
  10. A_G
  11. Adam_GS
  12. tourist
  13. Savior-of-Cross
  14. Matthew Allan
  15. uwu
  16. TLE

At this time, the scoreboard has been finalized, and you can upsolve our problems / watch our video tutorials with the following links:

Thank you for tuning into our contest! We hope to see you again at our Winter Contest next year~

Update: There is .35 HOURS LEFT before the qualification round. Submit your applications NOW so that they can be reviewed in time!

Please join our Discord server here for the latest information!

Hello Codeforces!

We (duality, antontrygubO_o, SHZhang, rqi, Tlatoani, enoone, codetiger927, czhang2718, bensonlzl, innocentkitten, keta_tsimakuridze, kingofpineapples, SuperJ6, flamestorm ), current students at MIT, are excited to announce our new contest — the MIT Informatics Tournament, M(IT)^2, 2024 Spring Invitational!

The contest will consist of two rounds: the Qualification Round and Final Round. The Qualification Round is an online two-hour individual contest that will take place from 1:00 — 3:00 PM ET on April 21st. We expect a difficulty distribution roughly ranging from Div. 2 A to Div. 1 E. We will offer the top three Qualification Round contestants monetary prizes. See the logistics page for more details.

The top 16 contestants will then be flown to MIT (we will cover all expenses and lodging), where they will compete in the Final Round on May 11th. The day of the Final Round is filled with exciting activities, such as fun tours around Boston, a fancy banquet, exclusive meets with our sponsors, and solving super cool (and hard) problems!

Note that due to logistical constraints, we can only fly contestants within the USA to MIT unless they arrange their own transportation and travel logistics. However, top internationals are still eligible for prizes in the Qualification Round.

For more information, check out our website, and the registration application is now open on a first-come-first-serve basis!

UPD: Contest is in around 20 minutes! Please, join!

UPD2: Thanks for participation! We apologize for some technical issues. Upsolving is available: MITIT 2024 Spring Invitational Qualification.

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SEERC 2023 and The 2nd Universal Cup. Stage 14: Southeastern Europe
By antontrygubO_o, 11 months ago, In English

ICPC Logo

Hi everyone!

2023 Southeastern Europe Regional Contest will take place on December 9. The contest was prepared by Pajaraja, milisav, bicsi, denis2111, antontrygubO_o, and RomaWhite.

Good luck to the official participants!

This contest will be used as Stage 14 of The 2nd Universal Cup (a week after the official contest). Therefore, we ask official participants to not publicly discuss the problems before the Universal Cup Stage.

You will be able to participate in the UCup contest in the following time windows:

Time windows

Thanks a lot to the Universal Cup committee for providing the platform.

About Universal Cup

UPD1: Contest livestream

UPD2: Here are Final Standings. Congratulations to the winners!

Place Country Team Name Contestant 1 Contestant 2 Contestant 3 Problems Penalty
1 Ukraine KhNURE_KIVI Denisov Valera_Grinenko Barichek 9 711
2 Ukraine KNU_0_GB_RAM KostasKostil kostia244 VladProg 9 998
3 Ukraine LNU Stallions PetroTarnavskyi mshcherba Yarema.st 9 1114
4 Serbia Infinity TadijaSebez nikolapesic2802 stefanbalaz2 8 427
5 Ukraine KNU_Banderolki danya.smelskiy Sonechko Markellonchik 8 834
6 Romania CodeBusters average_frog_enjoyer EmanuelDicu robxln 8 885
7 Romania Concret vladvlad00 status_coding a_dumi 8 959
8 Romania MLP popovicirobert loan toma_ariciu 7 566
9 Romania 3PeasInAPod BlueDiamond popabogdannnn livlivi 7 648
10 Romania UBB_Echipa_Misterelor georgerapeanu AlexPop28 AndreiCotor 7 731

UPD3: Editorial

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Problems that I authored so far
By antontrygubO_o, 21 month(s) ago, In English

Hi everyone! I wanted to write such a blog for a long time, motivated by similar blogs by adamant and by tibinyte; I finally decided to do it after my Universal Cup contest. This is not a super-comprehensive list, I also set some problems for some local contests, but that's most of it.

I want to encourage other setters to write such blogs. For me, it's very interesting to read about the backstories of some problems and also to see all the problems by some author gathered in one place (as most authors give problems to several platforms).

One important point. As you will see from the comments, many of my problems were improved by other people, and I myself improved some problems by other people. I think that it's crucial to have someone to discuss your problems with (apart from the coordinator).

So, here we go.

# Date Problem Contest Comment
1 June 2019 Vus the Cossack and Strings Codeforces Round #571 (Div. 2)
2 June 2019 Vus the Cossack and a Graph Codeforces Round #571 (Div. 2) My first problem
3 July 2019 Keanu Reeves Codeforces Round #572 (Div. 2) Split binary string into the smallest number of substrings, in each of which # of 0s is not equal to # of 1s. Initially, we wanted to ask to split into any number of substrings (and the model solution was to split into n characters), but we were told that this is not a real problem
4 July 2019 Number Circle Codeforces Round #572 (Div. 2)
5 July 2019 Candies! Codeforces Round #572 (Div. 2)
6 July 2019 Add on a Tree Codeforces Round #572 (Div. 1)
7 July 2019 Add on a Tree: Revolution Codeforces Round #572 (Div. 1) We were told to add this problem so that the contest would have at least some implementation
8 July 2019 Count Pairs Codeforces Round #572 (Div. 1) One of my best problems. Pinnacle of problemsetting...
9 July 2019 Make Equal Codeforces Round #572 (Div. 1) I came up with the statement, 244mhq with solution
10 July 2019 Problem from Red Panda Codeforces Round #572 (Div. 1) 244mhq came up with the statement, I with solution
11 August 2019 Choose Two Numbers Codeforces Round #580 (Div. 2)
12 August 2019 Make Product Equal One Codeforces Round #580 (Div. 2)
13 August 2019 Almost Equal Codeforces Round #580 (Div. 1)
14 August 2019 Shortest Cycle Codeforces Round #580 (Div. 1)
15 August 2019 Palindromic Paths Codeforces Round #580 (Div. 1)
16 August 2019 Almost All Codeforces Round #580 (Div. 1) One of my best problems. Unfortunately, a similar idea was used in a problem from IOI 2019
17 August 2019 Expected Value Again Codeforces Round #580 (Div. 1)
18 August 2019 Beauty of a Permutation Codeforces Round #580 (Div. 1) Sadly, I didn't know about permutation tree back then
19 October 2019 Find the Array SEERC 2019 My best interactive problem
20 October 2019 Cycle String? SEERC 2019
21 October 2019 Game on a Tree SEERC 2019 This is not a good problem, as it indeed is well known for general graphs... Don't do this
22 October 2019 Tree Permutations SEERC 2019
23 October 2019 Graph and Cycles SEERC 2019
24 December 2019 Make Good Good Bye 2019 I initially had solution only with adding $$$3$$$ elements. In testing, some testers discovered a solution with $$$2$$$ elements, and after the contest, we realized that it can be solved with only $$$1$$$ element!
25 December 2019 Strange Device Good Bye 2019
26 December 2019 Divide Points Good Bye 2019 One of my best problems
27 December 2019 Awesome Substrings Good Bye 2019 There is a very nice $$$n\log^2{n}$$$ solution, but we were not able to find it :(
28 December 2019 Subset with Zero Sum Good Bye 2019 One of my best problems. Initially, I was going to send it to IMO, and there was another problem at this position, but this problem by a recent round by hugopm turned out to be too similar to it :(, so we had to replace it.
29 December 2019 Xor on Figures Good Bye 2019 Initially, I sent it to IOI 2020, but then decided that it doesn't have meaningful subtasks and that it would be better to use it on CF. I wrote to the PSC and told them that I am retracting the proposal, apologizing. It seems that they missed my email, as in a few months, I received an email from PSC saying: The ISC would like to remind you that this strongly violates the rules of the IOI Call for Tasks, which requires all submitted tasks to be kept strictly confidential until the end of IOI 2020. In the future, if you would like to submit the task elsewhere and not have your task be considered for the IOI, you should email the host directly to let them know of this decision.
30 February 2020 So Mean Codeforces Round #618 (Div. 1) I just became a coordinator on Codeforces, and wanted to help to conduct the round as soon as possible, so I donated this problem. Now I don't think that it's a good problem... Mostly casework
31 March 2020 Kuroni and Impossible Calculation Ozon Tech Challenge 2020
32 March 2020 Kuroni and the Score Distribution Ozon Tech Challenge 2020
33 March 2020 Kuroni and Antihype Ozon Tech Challenge 2020 One of my best problems. Initially, the problem was about the general graph. Unfortunately, minimum arborescence solves the problem, so we had to adjust it this way.
34 July 2020 Integer Game Codeforces Global Round 9 244mhq suggested the setup, and I solved it. I will just leave this comment here
35 July 2020 Tree Modification Codeforces Global Round 9 This is one of the last problems which I created when I still thought that solution->statement is better than statement->solution is a much better way of problemsetting. This problem is a good example of why I switched... making statements not artificial with solution->statement is very hard.
36 September 2020 Permutation Forgery Codeforces Round #668 (Div. 2)
37 September 2020 Watermelon September Lunchtime 2020 (Div. 2)
38 September 2020 GCD operations September Lunchtime 2020 (Div. 2)
39 September 2020 Root the Tree September Lunchtime 2020 (Div. 1)
40 September 2020 Robot Detector September Lunchtime 2020 (Div. 1)
41 September 2020 Permutation Split September Lunchtime 2020 (Div. 1) I was thinking about this problem for quite some time in the background, and then at some point 244mhq brought up the following (old) problem: "Given a graph, check if we can split it into two graphs with same numbers of edges." I realized this problem was a partial case, but the statement was so natural, and the original problem wasn't too well-known from what I've searched, so I decided to still use this problem. Generally, using partial cases of some other problems is a very bad practice...
42 September 2020 Few Different Elements September Lunchtime 2020 (Div. 1)
43 September 2020 Adding on Segments September Lunchtime 2020 (Div. 1) My first problem that wasn't solved in the contest
44 November 2020 XOR-gun Technocup 2021 — Elimination Round 2
45 December 2020 String Operations Codechef December Challenge 2020 (Div. 1)
46 March 2021 Long Common Subsequence AtCoder Grand Contest 052
47 March 2021 Tree Edges XOR AtCoder Grand Contest 052 One of my best problems
48 March 2021 Nondivisible Prefix Sums AtCoder Grand Contest 052 The idea of the setup is by 244mhq in 2020, then I solved it and improved to the counting version
49 March 2021 Equal LIS AtCoder Grand Contest 052
50 March 2021 3 Letters AtCoder Grand Contest 052 One of my best problems. Thanks to maroonrk for coming up with this nice trick, my initial solution was much more complicated
51 March 2021 Tree Vertices XOR AtCoder Grand Contest 052 My second problem that wasn't solved in the contest
52 May 2021 Reverse Game SEERC 2020
53 May 2021 3-colorings SEERC 2020 Initially this was going to be used as AGC52F, but we were afraid of not intended solutions. Sadly, all AC solutions on the mirror were indeed not intended :( In the latter half of $$$2020$$$, I almost stopped coming up with problems; solution->statement didn't work well for me anymore, and I didn't believe I could come up with hard problems in the statement->solution way. This was the first hard problem that I came up with in statement->solution way, and it was the reason why I believed that I can make an AGC set; I messaged maroonrk after I came up with it.
54 May 2021 Divisible by 3 SEERC 2020
55 May 2021 Fence Job SEERC 2020 Initially, I wanted to solve the problem "Choose segment, replace all its elements by their OR, find the number of possible arrays", but my solutions turned out to be wrong. Then bicsi helped to revise the problem into this version
56 May 2021 AND = OR SEERC 2020 One of my few good data structure problems
57 May 2021 Modulo Permutations SEERC 2020
58 August 2021 Eulerian? GP of IMO
59 August 2021 Fancy Formulas GP of IMO
60 August 2021 Glory Graph GP of IMO I was inspired by the fact that for a graph, knowing all degrees, we can find the number of triangles plus antitriangles, so I was looking for some sort of relation for graphs on four nodes.
61 August 2021 Hamiltonian GP of IMO
62 August 2021 Intellectual Implementation GP of IMO I was once again inspired by this problem above, and thought that I can try to use this idea for counting something awful. Then, I came up with this statement, and 244mhq helped to solve it
63 August 2021 Joke GP of IMO
64 August 2021 K-onstruction GP of IMO Initially 244mhq proposed this problem, asking to construct a set of size at most $$$3\log{K}$$$ for a given $$$K$$$. We were then able to improve it to the bound in the statement.
65 August 2021 Little LCS GP of IMO Sorry for this problem... but if it fits anywhere, it's a camp training contest
66 September 2021 One Pile September Cook-Off 2021 (Div. 1) Utkarsh.25dec initially proposed version without counting (just determine who wins). I helped to make it harder, as we needed some hard problems for Cook-Off
67 October 2021 Permutating Inversions October Cook-Off 2021 (Div. 1) My third problem that wasn't solved in the contest. I wanted to add a pre-last problem to a Cook-Off, as I thought that the contest would be too easy otherwise. Apparently, this problem turned out to be the hardest, with 0 solves, with the next hardest problem having 1 solve...
68 October 2021 ABC Identity AtCoder Grand Contest 055 Jason Bourne 1
69 October 2021 ABC Supremacy AtCoder Grand Contest 055 Jason Bourne 2
70 October 2021 Weird LIS AtCoder Grand Contest 055
71 October 2021 ABC Ultimatum AtCoder Grand Contest 055 Jason Bourne 3. Initially, the problem was just to check whether a string is good ($$$N \le 2\cdot 10^5$$$), but then AmShZ submitted an unproven greedy in testing, and we were able to improve it to the current version
72 October 2021 Set Merging AtCoder Grand Contest 055 Certainly my best problem ever, and my fourth problem that wasn't solved in the contest. Read the comment for problem 55 from this list... I decided to solve this problem for OR when $$$a_i = 2^i$$$ initially, and bruteforce + OEIS showed that the answer is the number of sequences with LDS<=3. I was shocked and was stuck on proving this for three days until I finally realized the solution.
73 October 2021 Creative Splitting AtCoder Grand Contest 055 My initial proposal was: Let's call an array $$$a$$$ of length $$$2n$$$, consisting of integers from $$$1$$$ to $$$n$$$, good, if it is possible to split it into two subsequences of length $$$n$$$, such that in each subsequence $$$i$$$-th element doesn't exceed $$$i$$$ for every $$$i$$$ from $$$1$$$ to $$$n$$$. You are given array $$$a$$$ of length $$$2n$$$, where some numbers are given, and some are $$$−1$$$ (unknown). Find the number of ways to replace $$$−1$$$s with integers from $$$1$$$ to $$$n$$$ so that $$$a$$$ becomes good. With brute force, I knew that the number of "splittable" arrays is $$$\frac{(2n)!}{2^n}$$$ for several months, but I couldn't prove this. Thanks a lot to maroonrk for providing the proof and then for improving my initial proposal to this version.
74 November 2021 Many LCS SEERC 2021 Initially I needed length of order $$$\sqrt{K}$$$, thanks to Um_nik for improving the problem to the current constraints
75 November 2021 Max Pair Matching SEERC 2021
76 November 2021 ABC Legacy SEERC 2021 Jason Bourne 4
77 November 2021 Counting Phenomenal Arrays SEERC 2021
78 November 2021 LIS Counting GP based on SEERC 2021 I was really into LIS problems at the time...
79 December 2021 Sorting Segments SnackDown 2021 Online Elimination Round Yes, this is very similar to Stooge Sort, but I haven't heard about it before setting the problem
80 December 2021 Sorter Prodigy SnackDown 2021 Online Elimination Round Unfortunately, coincided with CCO '18 P6 :(. This happens
81 December 2021 Prefix Suffix LIS Constructing SnackDown 2021 Online Elimination Round
82 January 2022 Equal Number of Prefix Maximums SnackDown 2021 Final Round Unfortunately, this is an easier version of AGC028E :(
83 January 2022 Circular Permutation Recovery January Lunchtime 2022 (Div. 1) Unfortunately, this turned out to be an easier version of IOI 2020 plants...
84 January 2022 Divisible Distances January Lunchtime 2022 (Div. 1)
85 April 2022 Modular Circular Permutations April Lunchtime 2022 (Div. 1)
86 April 2022 Odd Split April Lunchtime 2022 (Div. 1)
87 May 2022 Doubled Distances May Cook-Off 2022 (Div. 2)
88 May 2022 Triple Inversions May Cook-Off 2022 (Div. 1)
89 May 2022 Different Subarrays Rearrange May Cook-Off 2022 (Div. 1)
90 May 2022 Split Powers Of 2 May Cook-Off 2022 (Div. 1)
90 May 2022 Max Min Circle Difference May Cook-Off 2022 (Div. 1)
91 May 2022 Plus Xor Increase May Cook-Off 2022 (Div. 1) Another rare good algorithmic problem...
92 May 2022 Make Grid Comparable May Cook-Off 2022 (Div. 1)
93 May 2022 Catch Me If You Can May Cook-Off 2022 (Div. 1) My fifth problem that wasn't solved in the contest
94 May 2022 Everything Everywhere All But One Codeforces Round #794 (Div. 2) Watch Everything Everywhere All At Once!
95 May 2022 Odd Subarrays Codeforces Round #794 (Div. 2)
96 May 2022 Circular Local MiniMax Codeforces Round #794 (Div. 1)
97 May 2022 Bring Balance Codeforces Round #794 (Div. 1)
98 May 2022 Permutation Weight (Easy Version) Codeforces Round #794 (Div. 1)
99 May 2022 Permutation Weight (Hard Version) Codeforces Round #794 (Div. 1)
100 May 2022 The Ultimate LIS Problem Codeforces Round #794 (Div. 1) One of my best problems
101 June 2022 Split AND Sum June Cook-Off 2022 (Div. 1)
102 June 2022 Prefix Suffix Distinct June Cook-Off 2022 (Div. 1)
103 June 2022 Max Minus Min June Cook-Off 2022 (Div. 1) This problem was initially proposed by jainmilind for $$$A, B, C \le 10^6$$$, I was able to improve it to the current constraints
104 June 2022 XOR, The Detective June Lunchtime 2022 (Div. 1)
105 June 2022 SPLIT With XOR Not X June Lunchtime 2022 (Div. 1) Filler problem, made just for all XOR contest
106 September 2022 Longest Unfriendly Subsequence EJOI 2022
107 September 2022 Permutations LCS EJOI 2022 Dear EJOI 2022 participants. I am deeply sorry for your destroyed mental health
108 September 2022 Anti-Increasing Addicts Codeforces Global Round 22
109 November 2022 Anti-median (Easy Version) Pinely Round 1 (Div. 1 + Div. 2)
110 December 2022 My Last ABC Problem AtCoder Grand Contest 059 From now on, only problems about 123
111 December 2022 Arrange Your Balls AtCoder Grand Contest 059
112 December 2022 Guessing Permutation for as Long as Possible AtCoder Grand Contest 059 When I first came up with a statement and solved it, I thought that the problem is standard and garbage. It turned out I was extremely wrong...
113 December 2022 Distinct Elements on Subsegments AtCoder Grand Contest 059 I came up with the statement in May of $$$2022$$$ and couldn't solve for three months.
114 December 2022 Grid 3-coloring AtCoder Grand Contest 059 Initially, I proposed a version with construction for $$$n<=100$$$, and my proof was extremely hard (and greedy). A week before the contest maroonrk realized that we can use the same idea as in AGC052E, and the problem became much nicer. Unfortunately, this idea turned out to be present in some papers...
115 December 2022 LIDS AtCoder Grand Contest 059 My sixth problem that wasn't solved in the contest, and, probably, the hardest problem that I ever made. In March 2022, I noticed that the number of permutations of length $$$n$$$ with $$$LIS = x, LDS = n+1-x$$$ is $$$C(n-1, x-1)^2$$$. (Yes, this is easy with the Robinson–Schensted correspondence, but I didn't know it). I was able to prove this only in August, and after finding a nice bijection in the process, I decided that I can try to write a third AGC.
116 December 2022 Divisible by 4 Spanning Tree SEERC 2022
117 December 2022 Exercise SEERC 2022
118 December 2022 Inadequate Operation SEERC 2022
119 February 2023 Adjacent Product Sum Universal Cup 1 Stage 4: Ukraine
120 February 2023 Binary Arrays and Sliding Sums Universal Cup 1 Stage 4: Ukraine
121 February 2023 Count Hamiltonian Cycles Universal Cup 1 Stage 4: Ukraine My initial solution was in $$$O(n^2)$$$, thanks to Um_nik for improving it to $$$O(n)$$$
122 February 2023 Distance Parities Universal Cup 1 Stage 4: Ukraine
123 February 2023 Excellent XOR Problem Universal Cup 1 Stage 4: Ukraine
124 February 2023 F*** 3-Colorable Graphs Universal Cup 1 Stage 4: Ukraine Like... who tf likes 3-colorable graphs?
125 February 2023 Graph Problem With Small $n$ Universal Cup 1 Stage 4: Ukraine This problem was born when me and 244mhq were discussing how to implement checker to Hamiltonian from our Ptz contest... We were surprised that we haven't seen it before, and it seems that almost no one has seen it. Apparently, Golovanov399 showed that this is standard exercise :(
126 February 2023 Help Me to Get This Published Universal Cup 1 Stage 4: Ukraine Please, help me to get this published
127 February 2023 Increasing Grid Universal Cup 1 Stage 4: Ukraine One of my most standard problems, but I decided that having such problem in an ICPC contest is good
128 February 2023 Jewel of Data Structure Problems Universal Cup 1 Stage 4: Ukraine
129 February 2023 King of Swapping Universal Cup 1 Stage 4: Ukraine
130 February 2023 Least Annoying Constructive Problem Universal Cup 1 Stage 4: Ukraine My best constructive problem
131 February 2023 Most Annoying Constructive Problem Universal Cup 1 Stage 4: Ukraine My seventh problem that wasn't solved in a contest, and the first one that wasn't solved in ICPC format
132 February 2023 No Zero-Sum Subsegment Universal Cup 1 Stage 4: Ukraine
133 December 2023 Jackpot SEERC 2023
134 December 2023 $K$ Subsequences SEERC 2023
135 December 2023 LIS on Grid SEERC 2023
136 December 2023 Max Minus Min SEERC 2023
137 March 2024 Charming Meals European Championship 2024 Just a few days before the contest, we realized that the problemset was too hard, and had to come up with something almost everyone would solve.
138 March 2024 Make Triangle European Championship 2024
139 May 2024 Distance Mod 5 MIT Informatics Tournament 2024 Finals
140 May 2024 Avoid XOR Zero MIT Informatics Tournament 2024 Finals We had to come up with a hard problem for finals, so I went to the usual place for inspiration: AtCoder. This problem is, obviously, heavily inspired by AGC065C
141 June 2024 Aibohphobia Universal Cup 3 Stage 4: Ukraine
142 June 2024 Breaking Bad Universal Cup 3 Stage 4: Ukraine
143 June 2024 Chemistry Class Universal Cup 3 Stage 4: Ukraine
144 June 2024 Daily Disinfection Universal Cup 3 Stage 4: Ukraine
145 June 2024 Equalizer Ehrmantraut Universal Cup 3 Stage 4: Ukraine
146 June 2024 Formal Fring Universal Cup 3 Stage 4: Ukraine
147 June 2024 Goodman Universal Cup 3 Stage 4: Ukraine
148 June 2024 Highway Hoax Universal Cup 3 Stage 4: Ukraine
149 June 2024 Increasing Income Universal Cup 3 Stage 4: Ukraine
150 June 2024 Jesse's Job Universal Cup 3 Stage 4: Ukraine
151 June 2024 Knocker Universal Cup 3 Stage 4: Ukraine Still hard to believe that it's solvable...
152 June 2024 Lalo's Lawyer Lost Universal Cup 3 Stage 4: Ukraine

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The 1st Universal Cup. Stage 4: Ukraine
By antontrygubO_o, 21 month(s) ago, In English

Hello everyone! The 4th Stage of the 1st Universal Cup: Ukraine, will be held on Feb 18th, 2023.

The contest is based on 1/8 and 1/4 Ukrainian stages of SEERC 2023, plus some extra problems. Please, don't participate, if you have seen these problems. This contest also serves as Day 1 in Osijek Competitive Programming Camp 2023 on February 18, 2023.

Author of all problems: antontrygubO_o. I hope you like the problems.

You can participate in the contest in the following three time windows:

  • Feb 18th 13:00 — 18:00 (UTC +8)
  • Feb 18th 19:00 — 24:00 (UTC +8)
  • Feb 19th 02:00 — 07:00 (UTC +8)

Please note that you can see two scoreboards in DOMjudge. The 'Local Scoreboard' shows the standings ONLY IN THE CURRENT TIME WINDOW. And the 'Combined Scoreboard' shows all participants, including the onsite participants, and the cup participants in the previous time windows.

Contest link: https://domjudge.qoj.ac/

Universal Cup Scoreboard: https://qoj.ac/ucup/scoreboard

About Universal Cup:

Universal Cup is a non-profit organization dedicated to providing trainings for competitive programming teams. Up to now, there are more than 200 teams from all over the world registering for Universal Cup.

A more detailed introduction: https://mirror.codeforces.com/blog/entry/111672

Register a new team: https://ucup.ac/register

UPD1: Thanks for your participation! Here is Editorial.

I also uploaded contest to gym: Anton Trygub Contest 1 (The 1st Universal Cup, Stage 4: Ukraine).

I hope to add ghost participants by tomorrow.

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Invitation to CodeChef February Cook-Off 2023 (Rated for all) — 08th February
By antontrygubO_o, 21 month(s) ago, In English

We invite you to participate in CodeChef’s February Cookoff 2023, this Wednesday, 08th February, rated for all.

Time: 8 PM — 10:30 PM IST

From admins. We apologize for the absence of Div. 1 contests. In the first half of 2022, we were trying hard to hold them on a regular basis. This was already challenging, as the number of high-quality proposals, especially hard ones, was very small; we had to use our own problems in almost every contest. This couldn't continue for long.

We would like Codechef Div. 1 contests to come back, but for this, we need your help. The Div.1 problems of the next few contests will be based on The Leo Camp 2022, a Ukrainian programming camp that took place in the summer of 2022, and, possibly, our own problems. But we need your problems to continue making these contests. So, if you have some original and engaging problem ideas, and you’re interested in them being used in CodeChef's contests, please, share them here.

If you participated in The Leo Camp 2022, please, don't participate in this contest.

Joining us on the problem setting panel are:

Written editorials will be available for all on discuss.codechef.com. Pro users can find the editorials directly on the problem pages after the contest.

The video editorials of the problems will be available for all users for 1 day as soon as the contest ends, after which they will be available only to Pro users.

Hope to see you participating. Good Luck!

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SEERC 2022 and Mirror Contest
By antontrygubO_o, 23 months ago, In English

ICPC Logo

Hi everyone!

2022 Southeastern Europe Regional Contest will take place tomorrow, on December 10. The contest was prepared by bicsi, antontrygubO_o, theodor.moroianu, lungualex00, eudanip.

Good luck to the official participants!

There will be a mirror of this contest this Sunday, December 11, 08:00 UTC. It will be held by the link https://seerc2022.eolymp.io/.

We hope that you will enjoy the contest! See you on the scoreboard.

UPD1: Congratulations to the winners of SEERC!

This year, the contest was held on two sites, Ukrainian and Romanian.

Standings and Top 5 of Ukrainian site:

Place Team Name Contestant 1 Contestant 2 Contestant 3 Problems Penalty
1 [Ukraine] LNU Stallions Yarema.st mshcherba PetroTarnavskyi 9 1091
2 [Ukraine] UzhNU_OLDS Fekete YaroslavBulyna illyakr 7 1129
3 [Ukraine] LNU NextGen FEREND Ebiarat RHplu51 6 916
4 [Ukraine] KhNURE_(-_-(-_-)-_-) log2win Phys-mat_KCh avoronoi 6 1044
5 [Ukraine] UzhNU_3yagoda VasyaMer tedi_2.0 Happy.CoDer 5 445

Standings and Top 5 of Romanian site:

Place Team Name Contestant 1 Contestant 2 Contestant 3 Problems Penalty
1 [Serbia] Infinity nikolapesic2802 TadijaSebez stefanbalaz2 11 1272
2 [Cyprus] bird-cherry buyolitsez GrandFruit step_by_step 10 1516
3 [Serbia] GII Klub MladenP milisav Pajaraja 10 1603
4 [Romania] Echipa Sarata alexandra_udristoiu popabogdannnn Stelutzu 9 1268
5 [Serbia] UoB R-Shuf Djordjevic VladaMG98 JovanB 8 1018

Once again, we invite you to the mirror tomorrow.

UPD2: Editorial

UPD3: The contest was uploaded to the gym: 2022 ICPC Southeastern Europe Regional Contest. I will add results of official participants soon.

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AtCoder Grand Contest 059 Announcement
By antontrygubO_o, 2 years ago, In English

I am glad to invite you to AtCoder Grand Contest 059. This contest counts for GP30 scores.

The point values will be added soon.

I would like to thank:

  • maroonrk for the amazing coordination of this round, for improving one problem, and for allowing me to host my third AGC (and third AGC in 2022). I also want to congratulate him on winning gold in ICPC 2021!
  • maspy, dario2994, errorgorn, timreizin, Um_nik, 244mhq for testing the contest.
  • MikeMirzayanov for the great Polygon platform

I really hope you will like the problems.

We are looking forward to your participation!

UPD1: Point values are $$$500$$$ — $$$700$$$ — $$$1100$$$ — $$$1100$$$ — $$$1400$$$ — $$$1900$$$

UPD2: Thanks for your participation!

The winners are:

1. ksun48

2. Petr

3. tatyam

4. hitonanode

5. tourist

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Invitation to CodeChef September Lunchtime (Rated for all) (Based on EJOI) — 23rd Sept
By antontrygubO_o, 2 years ago, In English

We invite you to participate in CodeChef’s September Lunchtime, this Friday , 23rd September, rated for all. It is based on EJOI 2022, the second day of which takes place earlier on the same day. All EJOI participants were asked to not discuss the problems before the end of this contest, and to not participate in this contest. If you somehow got to know some of the problems, please, don't participate.

Time: 8:00 PM — 11:30 PM IST

Please note that the contest duration is unusual — 3.5 Hours.

Joining me on the problem setting panel are:

The video editorials of the problems will be available for all users for 1 day as soon as the contest ends, after which they will be available only to Pro users.

Also, if you have some original and engaging problem ideas, and you’re interested in them being used in CodeChef's contests, you can share them here.

Hope to see you participating. Good Luck!

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C⊕deChef June Lunchtime (Rated f⊕r All) — 19th June
By antontrygubO_o, 2 years ago, In English

We invite you to participate in CodeChef’s June Lunchtime, this Sunday, 19th June, Rated for All.

Joining me on the problem setting panel are:

The video editorials of the problems will be available on our YouTube channel as soon as the contest ends. Subscribe to get notifications about our new editorials.

Also, if you have some original and engaging problem ideas, and you’re interested in them being used in CodeChef's contests, you can share them here.

Hope to see you participating. Good Luck!

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CodeChef June Cook-Off (Rated for All) — 5th June

By antontrygubO_o, 2 years ago, In English

We invite you to participate in CodeChef’s June Cook-Off, this Sunday, 5th June, Rated for All.

Time: 8:00 PM — 10:30 PM IST

Joining me on the problem setting panel are:

Also, announcing Scholarship for CodeChef Certification in Data Structure & Algorithms — More than 100 Indian participants in Divisions 1, 2, and 3 will win scholarships for the CodeChef Certification exam (discounted prices). Scholarship criteria can be found on the respective contest pages.

The video editorials of the problems will be available on our YouTube channel as soon as the contest ends. Subscribe to get notifications about our new editorials.

Also, if you have some original and engaging problem ideas, and you’re interested in them being used in CodeChef's contests, you can share them here.

Hope to see you participating. Good Luck!

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Editorial of Codeforces Round 794
By antontrygubO_o, 2 years ago, In English

I hope you enjoyed the round.

While problem D1B was good for balance in Div1, it was too hard for balance in Div2. I apologize for this.

Problem D1B = D2D is by dario2994. Other problems are mine.

D2A
D2B
D2C/D1A
D2D/D1B
D2E/D1C
D2F/D1D1
D1D2
D1E

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Codeforces Round 794 Announcement
By antontrygubO_o, 3 years ago, In English

We will hold Codeforces Round 794 (Div. 1) and Codeforces Round 794 (Div. 2).

The point values will be:

Div2: 500 — 1000 — 1500 — 2000 — 2500 — 2500

Div1: 500 — 1000 — 1500 — (1500 + 1500) — 3500

We are looking forward to your participation!

UPD 1: Thanks to NEAR for supporting this round, details can be found in this post.

UPD 2: Editorial

UPD 3: Congratulations to winners!

Div1:

1. Rewinding

2. jiangly

3. ecnerwala

4. gamegame

5. maroonrk

Div2:

1. lmqzzz

2. Teating_

3. lunchbox

4. Nida1097

5. demacia

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Invitation to CodeChef May Lunchtime (Rated for all) — 15th May 2022
By antontrygubO_o, 3 years ago, In English

We invite you to participate in CodeChef’s May Lunchtime, this Sunday, 15th May, rated for all.

Time: 8:00 PM — 11:00 PM IST

Joining me on the problem setting panel are:

Also, announcing Scholarship for CodeChef Certification in Data Structure & Algorithms — More than 100 Indian participants in Divisions 1, 2, and 3 will win scholarships for the CodeChef Certification exam (discounted prices). Scholarship criteria can be found on the respective contest pages.

The video editorials of the problems will be available on our YouTube channel as soon as the contest ends. Subscribe to get notifications about our new editorials.

Also, if you have some original and engaging problem ideas, and you’re interested in them being used in CodeChef's contests, you can share them here.

Hope to see you participating. Good Luck!

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Invitation to CodeChef May Cook-Off (Rated for All) — 1st May — My Round
By antontrygubO_o, 3 years ago, In English

We invite you to participate in CodeChef’s May Cook-Off, this Sunday, 1st May, Rated for All.

Time: 8:00 PM — 11:00 PM IST

Note that from this month, Cook-Off and Lunchtimes will be held on Sundays instead of on Saturdays.

Joining me on the problem setting panel are:

A couple of extra words about the contest:

  • All Div-1 problems have been set by me.

  • The contest is harder than usually, so the duration is changed to 3 hours instead of 2.5 hours

  • I hope everyone will enjoy the contest!

Also, announcing Scholarship for CodeChef Certification in Data Structure & Algorithms — More than 100 Indian participants in Divisions 1, 2, and 3 will win scholarships for the CodeChef Certification exam (discounted prices). Scholarship criteria can be found on the respective contest pages.

The video editorials of the problems will be available on our YouTube channel as soon as the contest ends. Subscribe to get notifications about our new editorials.

Also, if you have some original and engaging problem ideas, and you’re interested in them being used in CodeChef's contests, you can share them here.

Hope to see you participating.

Good Luck!

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Support Ukraine (Now with Crowdforces too)
By antontrygubO_o, 3 years ago, In English

I know that a lot of people here care about the war in Ukraine. If you are looking for ways to help, please, visit this link: http://linktr.ee/help_ukraine_global. Any support matters, any help matters.

Please, help to stop the bloody dictator of our neighbor.

UPD1: Another very good site

UPD2: With this website you can help to show Russians what's really going on in Ukraine. Props to this post.

UPD3: If your CF profile had country set to Ukraine at the moment of this post, and you haven't created Crowdforces account yet, you can do it by this link: https://nearcrowd.com/crowdforces, and receive 12 Near (which is around 100$ now).

You can find detailed instructions here. This document is available only in Ukrainian for now. Please, use this money for the maximum benefit.

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CodeChef January Lunchtime 2022
By antontrygubO_o, 3 years ago, In English

We invite you to participate in CodeChef’s January Lunchtime, this Saturday; 29th January from 8:00 PM — 11:00PM IST.

The contest will be 3 hours long. There will be 5 problems in Div 1/2 and 6 problems in Div 3. It will be rated for all three Divisions.

Joining us on the problem setting panel are:

The video editorials of the problems will be available on our YouTube channel as soon as the contest ends. Subscribe to get notifications about our new editorials.

Problem Submission: If you have original problem ideas, and you’re interested in them being used in CodeChef's contests, you can share them here.

Prizes:

  • The top 10 Global Division 1 users will get $100 each.
  • The top 100 Indian Division 1 will get Amazon Vouchers worth Rs. 1500 each.

Good luck and have fun!

P.S. I think that problems are interesting, I encourage everyone to try them!

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SnackDown 2021 Grand Finale, Parallel Contest & Closing Ceremony
By antontrygubO_o, 3 years ago, translation, In English

It’s finally time for one of the biggest events in the competitive programming world. The SnackDown ‘21 Grand Finale is here.

The entire Grand Finale event is scheduled to be completed in two days — January 8 (Saturday), and January 9 (Sunday).

For the Finalists

All the information has been shared over email, but summarising — The Grand Finale will be spread over two days and will be a closed event accessible only to the finalists, and a few invited guests. The SnackDown 2021 Final contest will be held on Jan 9th between 6:30 — 10:30 PM (IST).

For the last time for this SnackDown, meet the panelists!

For the Community

For those who would like to have a taste of the SnackDown Final problems, we also have the SnackDown Final Parallel Unrated Contest scheduled for January 9, 2022, 6:30 PM — 10:30 PM (IST). The problems will be the same as the Finale. Since the main Finals will be a restricted session, the rank list can be viewed here. Note that the rank list will be frozen for the last hour, and will be resolved in the post-contest ceremony on YouTube.

The Grand Finale Closing & Crowning Ceremony

The SnackDown ‘21 Finale closing ceremony will start on Jan 9th at 10.30 PM IST. It will be hosted by Kamil Debowski and Ashish Gupta, who will be analyzing the contest problems and the strategies and performances of the participants. This is also where you can witness the moment of truth, the SnackDown ‘21 Grand Finale winner announcement! Everyone is cordially invited to the event, and we request you to set your reminders here.

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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?

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Invitation to CodeChef SnackDown Elimination and Parallel Rated Contests
By antontrygubO_o, 3 years ago, In English

We are very glad to invite you to participate in SnackDown Elimination round! It will be rated for all participants.

60 participants will qualify for the finals from the Elimination round. They include:

  • The top 25 participants from the Elimination round.

  • Additional top 2 school participants

  • Additional top 2 female participants

  • Additional 31 Indian participants, including:
    • 10 top Indian participants

    • The next 15 Indian participants from the Elimination Round qualify provided they solve at least 2 problems.

    • 3 top Indian School participants

    • 3 top Indian Female participants

Those, who haven't advanced, are invited to participate in the Parallel rounds, which will be held for all divisions. All three rounds are rated too.

Time: 7:30 PM — 10:30 PM IST

Please note that the duration was initially written as 5 hours by mistake, it will actually be 3 hours. The Finals duration will also be less than 5 hours.

Joining us on the problem setting panel are:

Users who have qualified to participate in the SnackDown Elimination should not participate in the Parallel rounds.

The Div-1 Parallel round and the Elimination ranklists will be merged to determine the winners of the cash/Amazon voucher prizes.

If you have some original and engaging problem ideas, and you’re interested in them being used in CodeChef's contests, you can share them here.

Hope to see you participating. Good luck and have fun!

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SEERC 2021 and Grand Prix of Southeastern Europe
By antontrygubO_o, 3 years ago, In English

ICPC Logo

Hi everyone!

2021 Southeastern Europe Regional Contest took place on November 21. Here you can view the full standings.

Congratulations to the winners of the contest!

Place Team Name Contestant 1 Contestant 2 Contestant 3 Problems Penalty
1 [Taras Shevchenko National University of Kyiv] KNU_0_GB_RAM KostasKostil VladProg kostia244 13 1788
2 [Kharkiv National University of Radio Electronics] KhNURE_Energy is not over BigBag Barichek Mustang98 12 1274
3 [Lviv National University] LNU Bulldogs mshcherba Vasyl_Protsiv PetroTarnavskyi 11 1429
4 [Faculty of Computer Science, Belgrade] GII Klub milisav Pajaraja MladenP 11 1433
5 [V.N. Karazin Kharkiv National University] KhNU_OtVinta kilt_01 Stroustrup 13022001 11 1444
6 [University of Bucharest] Unibuc Scrambled Eggs Rpd-Strike theodor.moroianu livlivi 11 1527
7 [Taras Shevchenko National University of Kyiv] KNU_Duplee Sonechko danya.smelskiy stanislav.bezkorovainyi 11 1608
8 [University of Bucharest] EchipaDulce Usu Stelutzu alexandra_udristoiu 10 1350
9 [Kharkiv National University of Radio Electronics] KhNURE_Lacrimosa kupriyanov dendi239 viskonsin 9 1068
10 [Babes-Bolyai University] UBB_Zalau00 Bodo georgerapeanu AlexPop28 9 1183

There will be a Grand Prix of Southeastern Europe based on these problems this Sunday, November 28, 08:00 UTC. Here is the link to the OpenCup.

This year, the sets of SEERC and OpenCup are a bit different: OpenCup won't include a few easier problems from SEERC and will additionally include several harder problems. In addition, problems are shuffled, so don't follow the standings of the official contest too much.

The authors of the OpenCup set are eudanip, Um_nik, bicsi, RomaWhite, Andrei1998, and me, antontrygubO_o. After the contest, the editorials to both versions of the contest will be published, and both versions of the contest will be uploaded to the gym.

We hope that you will enjoy the contest!

UPD:

Editorials:

Both contests are uploaded to Gym:

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AtCoder Grand Contest 055 Announcement
By antontrygubO_o, 3 years ago, In English

I am glad to invite you to AtCoder Grand Contest 055. This contest counts for GP30 scores.

The point values will be 400 — 700 — 900 — 1200 — 1500 — 1800

I would like to thank:

Problem statements will be short again, and I really hope that you will like the problems. However, I have to warn you that contest will be closer to ABC than to AGC...

We are looking forward to your participation!

UPD1: Thanks for your participation!

The winners are:

1. ksun48

2. tourist

3. djq_cpp

4. hos.lyric

5. jqdai0815

Special congratulations to tranquility , the only person to solve F.

Sadly, nobody got E in the contest time, though a few people were close. I encourage you to try it, or to read editorial, I think that it's the best problem I ever invented.

I hope you enjoyed the contest!

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CodeChef October CookOff 2021
By antontrygubO_o, 3 years ago, translation, In English

We invite you to participate in CodeChef’s October Cookoff, this Sunday; 24th October from 9:30 PM — 12:00AM IST.

The contest will be 2.5 hours long. There will be 7 problems in Div 1/2 and 8 problems in Div 3. It will be rated for all three Divisions.

Joining us on the problem setting panel are:

Video Editorialists and Translators will be added a bit later

Problem Submission: If you have original problem ideas, and you’re interested in them being used in CodeChef's contests, you can share them here.

Prizes:

Global Rank List:

  • Top 10 global Division One users will get $100 each.
  • Non-Indians will receive the prize via money transfer to their account.
  • Indian users will receive Amazon vouchers for the amount converted in INR.

Indian Rank List:

  • Top ten Indian Division One coders will get Amazon Vouchers worth Rs. 3750 each.
  • The rest in the top 100 will get Amazon Vouchers worth Rs. 1500 each.
  • First-time winners in Div 2 who make it to the top 200 for the first time will get Amazon Vouchers worth Rs. 750 each.
  • First-time winners in Div 3 players who make it to the top 200 for the first time will get Amazon Vouchers worth Rs. 750 each.

The video editorials of the problems will be available on our YouTube channel as soon as the contest ends. Subscribe to get notifications about our new editorials.

Good luck and have fun!

P.S. Seriously, try it, I think problems are interesting :P

UPD1: Sorry for confusion, the duration is 2.5 hours.

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XXII OpenCup GP of IMO
By antontrygubO_o, 3 years ago, translation, In English

This summer, me and 244mhq held a contest in Petrozavodsk Programming Camp. $$$1$$$ problem was provided by gepardo, and we are very thankful for that, and other problems were created by us, 244mhq and antontrygubO_o. This contest will be held as an OpenCup contest on September 19, 11:00 UTC+3.

I and 244mhq are friends for long time, since our years of participation at IMO, and it's 244mhq who introduced me to competitive programming. Therefore, we decided to call this contest GP of IMO.

Link (OpenCup login needed to participate)

I will publish the editorial here soon after the contest ends.

Good luck and have fun!

UPD1: Shame on me, I forgot to thank testers of this contest: gamegame, Geothermal, nitrousoxide.

UPD2: Editorial

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Giving negative feedback to contests in comments
By antontrygubO_o, 3 years ago, In English

//This is a short post motivated by the comment section of the last Div2 round (and of several rounds before)

Every problemsetter tries to make his contest as good as possible, and is upset when something goes wrong. Most problemsetters don't set contests for money, the payments are not worth the time and efforts spent on coming up with problems, preparing them, and hosting the contest. The most rewarding thing in this process in not the money, it's to see contestants enjoying your problems.

That's why feedback is so important. If the comment section is filled with comments praising the contest, setter will most likely want to come back with another contest, and if it's filled with hate and offenses, it's possible that setter will just give up on problemsetting and won't want to host another round.

This means two things.

First, if you liked the round, or some particular problem, why not to write a comment about it? I am sure that most setters would really appreciate it, and feel more motivated to come up with problems like the one you liked. Positive comments from high rated contestants, or from experienced problemsetters matter especially, but I rarely see positive comments from such users.

Secondly, we should try to avoid hateful comments, or unconstructive criticism. This doesn't mean that there shouldn't be any criticism, it is necessary to help setters to improve, but not all criticism is good. Below I will give several comments, which, in my opinion, aren't the best way to express your opinion about the contests. I won't mentioning authors of these comments, as I don't want to call anyone out, and I myself sometimes left not very cool comments.

What's the point of leaving such comments? How will this help setters to improve in problemsetting? These comments are not even telling what's exactly is wrong with the contest — it's just hate and a complete lack of respect to the setters (though I would consider Codechef comment as a compliment).

This is another type of comments — just saying that some particular problem was bad/shitty. However, this isn't much better, as this still doesn't help setter to improve much, it just discourages him from writing any problems in the future. If you are criticizing some problem, tell what exactly was wrong about it: was it well-known, standard, was it too caseworky, or too implementation heavy, maybe the constraints were too strict?

Again, I am not saying that criticism of contests in comments is bad. Here are some good examples (in my opinion).

They aren't disrespectful to the setters, and the authors of these comments are saying what exactly they didn't like about the contest, so that setter can avoid such mistakes in the future.

People may have different opinions about what's a good problem, or what makes a contest good, and setters won't always take all the criticizing comments into account when hosting their next round, but the feedback is still very important for improvement. So, when you leave negative comments, please try to not use them as an opportunity to call the author a stupid moron. It's better to tell what exactly went wrong, politely and respectfully, without any hate. There aren't that many problemsetters out there, so instead of telling people to stop writing problems, it's better to support them.

:)

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SEERC 2020 and Grand Prix of Southeastern Europe
By antontrygubO_o, 4 years ago, In English

ICPC Logo

Hi everyone,

I am happy to announce that the 2020 Southeastern Europe Regional Contest will take place on May 23 at 10 am UTC+3. The link to the live results will be published here after the start of the competition.

Moreover, later this day, at 4 pm UTC+3, there will be the Grand Prix of Southeastern Europe based on these problems. Because of the Grand Prix, we are asking the official contestants not to discuss the problems in public.

After it, we will upload the contest to the gym and publish the editorial. We hope that you will enjoy the contest.

Good luck to all participants!

UPD. SEERC standings

UPD2. Congratulations to the winners!

Place Team Name Contestant 1 Contestant 2 Contestant 3 Problems Penalty
1 KhNU_OtVinta kilt_01 Stroustrup 13022001 8 1043
2 RAF Penguins Pajaraja milisav allllekssssa 8 1128
3 Echipa Dulce alexandra_udristoiu Stelutzu Usu 7 736
4 UAIC Endgame lungualex00 cristian1997 denis2111 7 837
5 KNU_stascool5 danya.smelskiy Sonechko stanislav.bezkorovainyi 7 1029
6 KhNU_GangBand dendi239 viskonsin Eikgrim 7 1230
7 cpu_goes_brrr muratt ykaya ekrem 7 1239
8 KhNURE_Energy is not over BigBag Barichek Mustang98 6 426
9 CodeBusters average_frog_enjoyer Hikori robxln 6 647
10 LNU Jackals BohdanPastuschak PetroTarnavskyi mshcherba 6 655

UPD3. Editorial

Thanks for your participation!

UPD4. The contest is available in gym:

2020-2021 ICPC Southeastern European Regional Programming Contest (SEERC 2020).

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