Codeforces Round #691, based on ByteDance — Moscow Workshops Online Contest  Hello, Codeforces community! I'm glad to invite you to Codeforces Round #691 (Div. 1) and Codeforces Round #691 (Div. 2), which will be held on [contest_time:1459]. **The round will be rated for both divisions.** The problems were taken (mostly) from the ByteDance — Moscow Workshops Online Contest, which is happening at the same time. They were prepared by me, [user:AndreySergunin,2020-12-17], and [user:amethyst0,2020-12-17]. We are very thankful to the testers: [user:low_,2020-12-18], [user:__rkm__,2020-12-18], [user:ecnerwala,2020-12-18], [user:Tima,2020-12-18], [user:IITianUG,2020-12-18], [user:thenymphsofdelphi,2020-12-18], [user:mohammedehab2002,2020-12-18], [user:namanbansal013,2020-12-19], [user:Redux,2020-12-19] for their time and great feedback. Also big thanks to Bytedance instructors [user:chenjb,2020-12-18] and [user:MiFaFaOvO,2020-12-18] for testing and r...

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Problem Topics Good Day to you! I've been asked to make some topic-wise list of problems I've solved. Even though I couldn't involve all problems, I've tried to involve at least "few" problems at each topic I thought up (I'm sorry if I forgot about something "easy"). I've alredy made such list once anyway I've tried to include more problems now &mdash; so here it is: <spoiler summary="aho"> http://www.spoj.com/problems/ADAJOBS/ URI 2226 (5) //[NICE][NUMBERS][DP] http://www.spoj.com/problems/SUB_PROB/en/ http://mirror.codeforces.com/contest/696/problem/D 8 http://www.spoj.com/problems/AHOCUR/ 5 //Aho-Corassic + DP https://www.codechef.com/problems/LYRC (5) //Sample aho-brute-force http://mirror.codeforces.com/problemset/problem/346/B //Proposed by [user:bradyawn,2019-08-03] </spoiler> <spoiler summary="automat"> 6861 [LA] //CYK UVA 10679 //Suffix Automat http://www.spoj.com/problems/STRMATCH/ //Suffix Automat &mdash; trie might do too http://www.spoj.com/problems/NSUBST...

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[Contest] Statement Not Found: Season 2 #### Do you think you can solve CP problems without reading the problem statements? Let's find out! On [August 28, 2022 (Sunday) 19:30-22:00 GMT+8](https://www.timeanddate.com/worldclock/fixedtime.html?msg=Statement+Not+Found+-+Season+2&iso=20220828T1930&p1=122&ah=2&am=30), I will hold an unofficial fun contest called Statement Not Found. As you can deduce from the title, there will be no problem statements (except title and samples). Your goal is to collect as many points as possible within 2.5 hours :) Obviously, this round is **unrated**. It is somewhere between April Fools contest and a legitimate contest. The contest will be OI-style, meaning there will be no time penalty. You are allowed to use any resources online to help solve the problems. There will be **12** problems. **Scoring Distribution:** 200-400-700-700-700-800-800-900-1100-1100-1100-1500 (Total: 10000) **Please read all problems** as problem difficulty is very subjective and a 1100-point problem might b...

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Codeforces Round #691 Editorial (finished) Keeping track of both Codeforces round and online team contest was a doozy, so this is only the best draft of the editorial I have. Missing problems will gradually be added, and existing explanations may improve over time. Hope you enjoyed the problems, and let me know if anything can be explained better! **UPD**: okay, all of the problems are out, and most of the bugs are fixed (I hope). By the way, we had a nice [discussion](https://youtu.be/1OWGTQpfk5Y) with [user:Errichto,2020-12-20] on his stream about Div. 2 problems, which some of you may find more approachable. Be sure to check it out, as well as other stuff [user:Errichto,2020-12-20] creates! [tutorial:1459A] [tutorial:1459B] [tutorial:1459C] [tutorial:1459D] [tutorial:1459E] [tutorial:1459F] [tutorial:1458E] _(Kudos to [user:Golovanov399,2020-12-19] for his neat [grid drawing tool](https://golovanov399.github.io/grid/rect_grid_draw.htm))_ [tutorial:1458F]

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Practice Educational Round Problems by tags Problems in educational rounds are generally straightforward and I've found them helpful for practising a new concept. I wrote a little python script for myself which uses the CodeForces API to fetch problems across all educational rounds, sorted by the difficulty in chosen tags. (There's no way as far as I can see to do this on the platform itself) I'm sharing it here in case someone finds it helpful: https://github.com/yashrajkakkad/cf-educational. Sample output when tags='dsu': 1400 News Distribution https://www.codeforces.com/problemset/problem/1167/C 1700 Swaps in Permutation https://www.codeforces.com/problemset/problem/691/D 2000 Imbalanced Array https://www.codeforces.com/problemset/problem/817/D 2000 SUM and REPLACE https://www.codeforces.com/problemset/problem/920/F 2100 Connected Components? https://www.codeforces.com/problemset/problem/920/E 2100 Minimum spanning tree for each edge https://www.codeforces.com/p...

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[Решено] Пример распараллеливания на codeforces и один маленький вопросик Есть две посылки на `C#`: с [многопоточкой](http://mirror.codeforces.com/contest/691/submission/19309384) &mdash; **Accepted** и [без многопоточки](http://mirror.codeforces.com/contest/691/submission/19308685) &mdash; **TLE**. Автор решения использует `Parallel.For` в функции `MultiplyMatrixPow`, за счет чего и добивается успеха. **Вопрос**: сколько ядер мы можем нагружать на серверах codeforces при проверке нашего решения? **UPD:** Многопоточка здесь ни при чем. В первом решении автор берет остаток от деления три раза, во втором всего один. Отсюда и выигрыш.

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Topcoder Single Round Match 691 Hi there! Today at [18:00 MSK](https://www.timeanddate.com/worldclock/fixedtime.html?msg=SRM%20691&iso=20160530T1500&ah=2&am=0) will be held [Topcoder SRM 691](https://community.topcoder.com/tc?module=MatchDetails&rd=16730). Let's discuss problems after contest!

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Tracking Codeforces Educational Rounds - Educational Codeforces Round 1 (http://mirror.codeforces.com/contest/598) - Educational Codeforces Round 2 (http://mirror.codeforces.com/contest/600) - Educational Codeforces Round 3 (http://mirror.codeforces.com/contest/609) - Educational Codeforces Round 4 (http://mirror.codeforces.com/contest/612) - Educational Codeforces Round 5 (http://mirror.codeforces.com/contest/616) - Educational Codeforces Round 6 (http://mirror.codeforces.com/contest/620) - Educational Codeforces Round 7 (http://mirror.codeforces.com/contest/622) - Educational Codeforces Round 8 (http://mirror.codeforces.com/contest/628) - Educational Codeforces Round 9 (http://mirror.codeforces.com/contest/632) - Educational Codeforces Round 10 (http://mirror.codeforces.com/contest/652) - Educational Codeforces Round 11 (http://mirror.codeforces.com/contest/660) - Educational Codeforces Round 12 (http://mirror.codeforces.com/contest/665) - Educational Codeforces Round 13 (https://mirror.codeforces.com/contest/678) - Educational Codeforces Round 14 (https://mirror.codeforces.com/contest/691) - Educational...

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Educational Round Problem Hello my submission for the problem http://mirror.codeforces.com/problemset/problem/691/D gets MLE while I have seen similar solutions getting passed using lesser memory.Can someone explain what is the reason behind it. My submission http://mirror.codeforces.com/contest/691/submission/19745411 & other similar solutions are http://mirror.codeforces.com/contest/691/submission/19081882 & http://mirror.codeforces.com/contest/691/submission/19274092 & http://mirror.codeforces.com/contest/691/submission/19107997. Thanks!

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Weak test case for problem 1771C (Problem no C of last round) I wasn't happy with the time complexity of my solution. So, I was looking for a solution with improved time complexity. And I found this. This guy solved this problem by only checking the first 200 elements after each index and comparing GCD of each pair . He won with the power of probability! His submission: [submission:184781213] <spoiler summary="Test Case"> 1 201 211 223 227 229 233 239 241 251 257 263 269 271 277 281 283 293 307 311 313 317 331 337 347 349 353 359 367 373 379 383 389 397 401 409 419 421 431 433 439 443 449 457 461 463 467 479 487 491 499 503 509 521 523 541 547 557 563 569 571 577 587 593 599 601 607 613 617 619 631 641 643 647 653 659 661 673 677 683 691 701 709 719 727 733 739 743 751 757 761 769 773 787 797 809 811 821 823 827 829 839 853 857 859 863 877 881 883 887 907 911 919 929 937 941 947 953 967 971 977 983 991 997 1009 1013 1019 1021 1031 1033 1039 1049 1051 1061 1063 1069 1087 1091 1093 1097 1103 1109 1117 1123 1129 1151 1153 1163...

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Problem with solutions: are they bugs? I have just submitted my solutions to [problem:691D] from [contest:691]. They are [submission:19226396], [submission:19226642] and [submission:19226815]. Test #2 is ~~~~~ 1 1 1 1 1 ~~~~~ I ran my solutions on my machine, compiled with standard command line (`g++.exe -static -fno-optimize-sibling-calls -fno-strict-aliasing -DONLINE_JUDGE -lm -s -x c++ -Wl,--stack=268435456 -O2 -o D.exe D.cpp`). They all output 1. However, they all got RTE on Codeforces online judging system. Is there a bug on Codeforces or are my solutions wrong?

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Difficult icpc problem hey, can someone please help me with this problem? [https://icpcarchive.ecs.baylor.edu/external/74/7401.pdf](https://icpcarchive.ecs.baylor.edu/external/74/7401.pdf) https://icpcarchive.ecs.baylor.edu/index.php?option=com_onlinejudge&Itemid=8&category=691&page=show_problem&problem=5423 You are given an infinite binary indexed tree, where each node's value is its index. You're also given two integers, _N_ and _K_. you're supposed to print a walk on this tree, where each node you visit, you either **add** or **subtract** it to your sum. The length of the walk must be _K_ and the final sum must be _N_. thanks.

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Educationals Rounds Link (From Starting) I saw on Codeforces on a regular basis, that there are a lot of questions and answers about practicing and practicing more. Although It is my opinion that the Educationals Rounds are best for this, at least for people like me. They learn from it and the problems are very nice and interesting. There are many Educationals Rounds will come and I will also try my best to keep this blog update. Although if you want to generate these links <s>at any time</s> locally you can find the code on my GitHub repo: https://github.com/adshin21/Codeforces-Contest-Selector-By-Div-s So I've collected the links for all the educationals rounds that has happened. <table class = "bordertable" align="center"> <tbody> <tr> <td>Educational Round 1 </td> <td> <a href= " http://mirror.codeforces.com/contest/598" >http://mirror.codeforces.com/contest/598</a></td> <tr> <tr> <td>Educational Round 2 </td> <td> <a href= " http://mirror.codeforces.com/contest/600" >http://mirror.codeforces.com/contest/600</a></td> <tr> <tr> ...

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C++11 VS C++14 http://mirror.codeforces.com/contest/691/submission/20656594 http://mirror.codeforces.com/contest/691/submission/20656228 I wonder why one is AC but the other got TLE. http://mirror.codeforces.com/contest/710/submission/20661365 http://mirror.codeforces.com/contest/710/submission/20661475 And one is AC but the other got CE.

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Swaps in Permutation problem(solved,a stupid bug:DDD) Hi all, I have difficulty on a problem on codeforces http://mirror.codeforces.com/problemset/problem/691/D my submission is : http://mirror.codeforces.com/contest/691/submission/19308291 I think my idea is right, I used dsu to group several numbers and downsort numbers inside the groups. But I don't know why I am still wrong answer at test21. The idea is simple, but I can't find what's wrong. Anyone please help me, thanks:D How to find bugs when you think your algorithms and implementation is correct,BTW? Edit: Bug found:))) I should calculate p[i]=parent(i) before I use p[i] . I thought it was automatically done by merging, however it is not :DDDD

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TopCoder SRM 691 Can anyone post a detailed solution to Div 2 500 pointer of SRM 691 ?

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All DIV 3 contests links for practice Hello friends I am sharing the link of all div 3 links for practice. -------------------------------------------------------------------- <br><br> Div3 1: https://mirror.codeforces.com/contest/977<br> Div3 2: https://mirror.codeforces.com/contest/978<br> Div3 3: https://mirror.codeforces.com/contest/988<br> Div3 4: https://mirror.codeforces.com/contest/999<br> Div3 5: https://mirror.codeforces.com/contest/1003<br> Div3 6: https://mirror.codeforces.com/contest/1005<br> Div3 7: https://mirror.codeforces.com/contest/1006<br> Div3 8: https://mirror.codeforces.com/contest/1015<br> Div3 9: https://mirror.codeforces.com/contest/1029<br> Div3 10: https://mirror.codeforces.com/contest/1066<br> Div3 11: https://mirror.codeforces.com/contest/1077<br> Div3 12: https://mirror.codeforces.com/contest/1092<br> Div3 13: https://mirror.codeforces.com/contest/1095<br> Div3 14: https://mirror.codeforces.com/contest/1102<br> Div3 15: https://mirror.codeforces.com/contest/1108<br> Div3 16: https://mirror.codeforces.com/contest/1118<br> Div3 17: https://mirror.codeforces.com/contest/113...

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Different answer on Codeforces compiler and local compiler I have the following submission for problem 691D: http://mirror.codeforces.com/contest/691/submission/19104383 It says wrong answer on test 3.However I get the correct answer on my codeblocks compiler.

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Teams going to Gwalior/Pune Regionals **UPDATE:** I've uploaded the code that I used to generate this on Github, in case someone needs to generate something similar: [Codeforces Team Rating Calculator](https://github.com/abdullah768/Codeforces-Team-Rating-Calculator) The regional round has ended and here's the final Ranklist: https://www.codechef.com/public/rankings/ACM18GWR Inspired by the list of teams going to Kharagpur regionals, I decided to make one for Gwalior/Pune regionals. The list contains all the teams from the official Gwalior website. If you know the usernames of members of any of the teams. Please update the excel file: ### [HERE] (https://docs.google.com/spreadsheets/d/1jRvwzQzp1DOcazgI7jXBB8uY3u7Ze_eQ77Xa75_Q810/edit?usp=sharing) Team rating calculation has been done according to the official Codeforces team rating calculation formula. The table will be updated with details from the excel file every 6 hours or so. Last Updated: 10 pm, 12th December IST | No. | AIR | Team Name ...

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