Добрый вечер!
Завтра в 16:00 по Москве состоится финальный раунд Coder-Strike 2014, задачи которого, как и задачи всех предыдущих раундов Coder-Strike, готовили: Gerald, HolkinPV, Igor_Kudryashov.
Есть хорошая новость: рейтинговая трансляция раунда будет проводиться как для первого дивизиона, так и для второго. Конечно, специально для второго дивизиона в контест будут добавлены простые задачи и, как вы уже догадались, будут убраны сложные.
Регистрация на контест откроется сегодня в 4:00 ночи по Москве, закончится она за 5 минут до начала соревнования. Неофициальные участники из первого дивизиона должны регистрироваться на контест "Coder-Strike 2014 — Финал (трансляция, Div. 1)", неофициальные участники из второго дивизиона на контест "Coder-Strike 2014 — Финал (трансляция, Div. 2)", официальные участники на контест "Coder-Strike 2014 — Финал".
Надеюсь, что задачи раунда вам понравятся, мы очень старались хорошо их подготовить.
Желаю удачи на контесте!
UPD. В связи с проведением онсайта соревнования Coder-Strike 2014, мы вынуждены ограничить доступ к сайту на время подведения итогов. Ориентировочно, сайт будет недоступен 15-30 минут после окончания контеста.
Упала задача B или C, прочитай разбор задач! :]
У нас в это время сдача ДЗ по хаскелю и лекция по линалу, не могли бы перенести на пару часов вперёд? Знаю, что поймёте и не откажете, так что заранее спасибо, вот от души, правда.
Я не думаю, что твои преподаватели читают CF. Лучше к ним лично обратиться. Но я все равно сомневаюсь, что они будут переносить сдачу на пару часов вперед из-за какого-то там контеста.
http://vk.com/itmotrains?w=wall-66422738_58
А у меня промежуточный экзамен по дискрет математике. Жаль что придётся отклонить этот раунд.
Why are there 3 contests pending? Is the 3rd one dedicated to on-site participants? Edit: What's wrong with asking for a clarification about something everybody wants to know better about?
exactly :)
What is the duration of the contest?
As always, 2 hours.
Contests --> current or upcoming contests !
Thanks, it was not posted when I wrote this.
Will the online version be rated ? EDIT : Sorry for having not seen the announcement of Round 2 >_<
Почему у меня открыта регистрация на официальный финал, если я занял во втором туре 37-ое место?
То, что ссылка есть, не означает, что вы можете зарегистрироваться.
Will the level of the problems will be same as the normal rounds of codeforces (or even round 1 of coder strike). Are they gonna be harder? I'm talking about div 2.
They will probably be quite the same. It is said:"Of course, we've added simple problems in the second division contest (and also deleted hard problems)." So, yes, I think they will be the same difficulty as usual for div2 :D
Hope so :D
Will practice session be unrated for all participants?
Practice session is only for the onsiters. For sure, it will be unrated.
Before 20 minuets I saw that "Coder-Strike 2014 — Finals" duration is 25 minuets. But now I am seeing that it is 2 hours. Why? Has the duration changed or I was wrong?
I think that 25 minutes is the duration for Coder-strike 2014-Finals(practice session) The real contest will have 2 hours :) Maybe you have seen it wrong...
На вкладке "Соревнования" циклическое перенаправление. Жестоко :).
уже работает)
The contest is delayed by 15min?
It seems to be delayed ...
I think it is because there are some coders who haven't registered the first contest...
yes!!!! the reason could be something official related......
upd: Now 25 minutes!! :P
probably the participants are having dinner! ;)
what a special reason...
dinner at 4PM!!!! Sarcasm!! :D
what about afternoon tea?
i think the reason could be practice session !!
Four-o'clock tea xD
see UPD3 of this blog post :D
that was 7.30PM!!! :D
Is anyone else having trouble clicking on the "Contests" tab? I am getting "This webpage has a redirect loop" on Google Chrome.
Yeah, me too. It's very frustrating. I hope that when the contest starts, it will work well :)
still have troubles??? it works fine for my google chrome.
UPD: Now i am facing problem......
anyway, click on http://mirror.codeforces.com/contests/423,419,420,421 instead of contest tab.
Clear the cache memory in Google Chrome
Thanks, this fixed it for me (for now) :)
Again and again delay!! x-( x-(
"This webpage has a redirect loop" . what's wrong with contests page ?
delay 30 minutes !!!!
new time is 4:15..... be updated or u will get 10 minutes penalty!! :)
Like I was 3 minutes late ... :/
Why are u delaying this??? Have any reason? 4:00 --> 4:15 -->4:20 and now 4:25 Stop doing it! Start the contest!!!
new time is 4:15
Contest will start at 16:10 + 5*floor(3*rand()) :)
Don't delay any more cause I will leave at 17:20 (21:20 here at China) and go to sleep...
Ok, just for you.
why should you go to bed so early?
"Contest has been finished" :P
I even haven't started yet!
The practice round has ended, that's true for sure.
But I'm not onsite participant!
that was the practice session. even i initially thought like u, but when i saw the timer of practice contest as
00:00:00, i guessed this must be the meaning.3 contests are gonna start at the same time! Hope that the website won't be down.
-"Contest is over, would you like to see the results?"
-"Yes"
-"You are not allowed to view the contest" :|
Help provided by organizers during contest .. .12757 A 22.04.2014 16:39:05 What kind of unhelpful attitude is this? No comments 12756 A 22.04.2014 16:39:04 What kind of unhelpful attitude is this? No comments 12749 A 22.04.2014 16:29:11 Problem not available in English Without Google Translate? Input Converted to getting dates After Translation Please Look into it. No comments 12748 A 22.04.2014 16:29:11 Problem not available in English Without Google Translate? Input Converted to getting dates After Translation Please Look into it. No comments 12746 A 22.04.2014 16:28:43 Problem not available in English with Google Translate? Input getting converted to dates after translation please look into it. No comments
If you're complaining about something, write properly what it is. All you're doing is giving random (from the POV of anyone who doesn't know what you mean beforehand) numbers, dates/times (why point out today's date, anyway?) and repeating sentences.
Many people solved problem A within one minute, and got 500 pts!
They probably have reading and coding speed over 9000. rares.buhai read and solved in 5 seconds.
I think he cheated. He might have known the problem.
Actually I solved it in 0 minutes as well. It looks like the timer started later than the problems became available. So I've seen the problem, written the code and submitted it and then I saw that it show that there ~1 hour 59 minutes left in the contest. I see that my local file was modified at 16:19 MSK, 4 minutes after the contest started, not sure why it was counted as 0 minutes.
This is because of my mistake. We have a lot of movements on the onsite, and I've made a mistake while changing time of the first division contest.
So,the actual duration is 2hours & 4minutes?
Seems so. This should be unrated based on precedent — in some not very old contest on CF, sone people had access to the problems because of a bug, and it was unrated. This is almost the same situation.
Yeah, I can remember that, same situation .... but that doesn't make this same round need to be unrated
it seems both of you will loose rating if it is rated :P
I probably will, but not much (I lost a lot last time and got a better place now). I might even gain a bit, but that people could submit at 0 minutes bugs me anyway.
I thought today everybody had access to problems 4 minutes before the timer started.
But not everybody knew. I only read the problem when the timer said that trying wouldn't be a waste of time. There are better things to do before a contest than holding F5.
Well, I was online at the point when the round started and I got a notification that round has started asking whether I want to proceed to to the problems. And I didn't notice the timer issue until I have already submitted the first problem. Are you saying that you didn't got the notification?
I'm quite happy to see it was rated even though my rating declined back, that's what I earned in this contest.
AFAIK the notification showed for me at the supposed start time, not 4 minutes earlier.
And that seems to be exactly the time we started. We didn't start BEFORE the supposed time (16:15 MSK), the timer started later. Strange thing is that you look into my and your attempts it seems to show the correct time for both of us — you seem to submit the problem one minute earlier than me. But mine is counted as 500 points (first minute of contest) and yours is counted as 494 points (forth minute of contest). So I suppose the timer was tweaked between our attempts were made and the only thing required to make these results absolutely fair is to recalculate the points given to each contestant for each problem.
That'd be good, then. It'd also be nice to get an opinion of someone who can see into the system.
I wonder what would have happened if somebody submitted before the timer started... more than 500 points? :D
Div 1 contest started 4 minutes after div 2 contest. I think they cheated
Мне удалось понять условие D div2 ! Про С такого не скажу)
UPD кстати, проверьте идею по D: Посчитаем для всех i количество тех, кто против i (сохраним в cnt[i]). Отсортируем. Потом пройдем по i, если cnt[i] >= p, то прибавим к ответу n-i, иначе найдем в cnt позицию j (бинпоиск) числа cnt[i] — p из i..n, если надо, округлим найденное до i+1. Потом прибавим к ответу n-j+1. Ответ в ллонг.
UPD2 это неправильно. Как надо я не понял, но одно ясно — ответ иногда должен быть меньше, чем у этого решения.
Тоже не сразу понял и получил WA 5. Нужно было найти число пар, где количество разных людей обвиняют кого либо из этой пары. Таким образом, нельзя просто посчитать число пар, у которых сумма больше либо равно p.
И как такое решать?
Почти так же, только когда выбираешь одного (назовем его X), то предварительно вычитаешь у всех Y, за которых голосовали одновременно с Х (то есть если кто-то проголосовал Х или Y). Считаешь, потом возвращаешь их обратно.
Условие задачи А спецом писали чтобы взломов меньше было? Ведь немного изменив условие было бы интереснее. Например, сказав что ответ не всегда существует.
Как говорится, поспешишь — людей насмешишь. В данном случае я и сам изрядно посмеялся :D
Зато 4 взлома, жаль что себя ломать нельзя :D
У меня в комнате, только 2-е таких было к сожалению
Попробую угадать. В D решение за mlogn неявным декартовым деревом. Выполняем запросы в обратном порядке и смотрим, не получилось ли чего противоречивого. Я прав?
Зачем в обратном? Можно в самом что ни есть прямом.
Ну, мы ведь тогда получим конечную последовательность, а не начальную, не?
Я в вершинах дерамиды хранил первоначальные индексы, а ответ записывался в массив.
Можно просто хранить в узле еще и начальную позицию.
Блин, точно... В таком виде её и вовсе можно без дерамиды решать. Сейчас попробую.
UPD: Дорешка не открыта ещё Оо. Ну, значит, не совсем сейчас.
А можно и без декартового дерева. Просто дерево отрезков с первыми m фейковыми элементами, и поддерживать 0 - 1 сумму на подотрезках.
Div2 D , wrong ans on pretest 5 :(. my idea was : for each i , if(freq[i]>=p)res+=(n-1); else { for each j=p-freq[i] to n res+=(number of numbers that exists j times) if(freq[i]>=p-freq[i])res-- } res/=2
is it a wrong idea? [freq[i] means frequency of i, how many coders have voted i]
Perhaps I misunderstand you, but a programmer does not agree twice with his choices. For example if we have
Then answer should not count (1,2) even though the pair (1,2) has frequency 3 — the first coder can only agree once.
Thanks a lot, You saved my lots of time of mine. You exactly got my Bug. thanks again.
If test is like
4 4 3 4 3 4 1 2 1 2, you cannot choose (1,2) or (3,4) because of only two coders agreed with it. I suppose.Thumbs down for a contest starting at past 19 minutes. I had just finished D when I saw the contest ended at past 19 minutes. This is said in a constructive way, I'm sure this confused a lot of coders.
If site access needed to be blocked couldn't you have at least run system testing while we waited :(
Very fast system test! I take it back! :)
Как делать E?
А вроде в лоб можно. Для каждого круга будет относительно немного расстояний до плоскости, на которых может быть пересечение, потому что d >= 5, а r <= 50. То есть для каждого круга будет не больше 2 * r / d + 1 = 21 пересечений. Идем по каждому кругу, находим подходящие расстояния, вычисляем угол, в котором мы будем попадать в этот круг. Дальше эти углы будут давать +1 внутри угла, по сути это нахождение точки, принадлежащей максимуму отрезков.
why there is no register for practice button?
Only 5 pretests for problem C .....:(
EDIT: Strange thing: Same problem in div 2 ( Problem D ) has 7 pretests...!
Only 5 pretests for E. It's as effective as blind submissions.
It was div 1's problem C :)
How did you count pretests??!
Look at the "Status" page. Check the nearest "failed test #x" and "failed pretest #y".
A.Some coders got "Wrong answer of pretest 5" during the contest
B.lots of coders got "Wrong answer of test 6" after systest
A, B => There were 5 pretests for C
:D
No I said that about div 2 D.
A.Maximum number of WA on "pretest" was 7
B.Minimum number of WA on "test" was 11
How did you found that it had 7 pretests?!!
No, There is a "TLE on test 8"
see his last submission:
:D
Your right ;)
И как все-таки решать B-div1? Моя идея была в том, чтобы помечать некоторых людей как плохих в трех случаях:
Что я не учел?
Вариант, когда он в какой-то момент точно не присутствует на митинге, и тут кто-то удаляется.
facepalm.jpg
А во 2 случае, если в "логах" не было его добавления — вы помечаете, что те кто упоминались (+ или — разницы нет) до него в логах никак не могут быть лидерами?
Задача становится простой, когда понимаешь, что из всех людей в логе — только один кандидат на лидера.
А когда дорешка откроется???
Сразу как только мы разберемся с onsite соревнованием. Это произойдет в ближайшее время.
Problem D of Div 2 was really interesting!
Problem B is the kind of problem that only looks very easy and in fact requires a very creative idea. Is anybody available to give a little hint? Don't spoil it all (yet), please.
Remember a set of all possible leaders (everyone can be a leader at the beginning) and update it as you process the queries.
Here are some observations
Participants who haven't participated in the log in/off operations all can be leaders.
From the remaining participants ... there can't be more than one leader from them.
Whenever a participant log in/off and there are other participants already logged in, then he can't be a leader.
У меня решение Div1-B на вот такой тест:
Отвечает:
При этом прошло систест. Я ведь не туплю после контеста и это действительно ненормально? о.о
У меня выдаёт
Кто-то точно не прав =)
Нет: первого точно не было в комнате, когда пришёл второй. Правильно
Авторское решение дает правильный ответ, к сожалению, не удалось учесть все неправильные решения. В этой задаче это было не так просто. =(
Why can't I see other people's solutions yet?
system test is quite fast...But how long does the rating update?
about 30 mins has passed since the system testing has ended. I don't know why the rating are not updating...
Maybe because there's the question of whether they should be updated at all. Something's seriously wrong when there are 5 second submissions.
I am afraid this contest will be unrated... because the div1 is started later than div2.... and it seems rating was not updated until now...
But that doesn't change anything for Div2, does it?
Yes....actually what I want to know is how to do with this mistake...
How is it possible to hack without submitting a solution? See picture. Was checking the tail end to see how many people actually submitted anything and came across this.
My guess would be: submit a problem, lock it, make a hack and then get your submission banned by the cheater detection system.
Yes...his or her A and B submissions were skipped....
Ahhh, that's exactly what happened (submission history shows skipped submissions for him). Thanks! :)
If you actually check his submission history, you will find that he did made submissions but for some reason these submissions are skipped and hence not shown in the standing list.
Why it took so much to be able to run practice?I have 2 sources ready to be submit and I'm very anxious to see if they work...
А что за хитрый 13й тест по задаче C div1? Очень у многих упало
Тем временем codeforces снова радует нас своевременными напоминаниями)
Большое спасибо, что напомнили, я уж боялся, что пропущу)
When will the ratings be updated ???
A humble request to codeforces' admins, please don't make this round unrated.
-On behalf of all participants who did better than usual.
and the other half are worse than usual :(
I think there is no strong logical reason for the contest to be unrated!
Don't worry!
Разбор есть — дорешки нет:)
Please make it rated.
in contest 234 Div 2, Problem B changed to another one, after 1 hour of contest. and contest was rated ! I think this contest will be rated !
That affected all participants equally. Wrong timer gives an advantage to people who tried to read the problems before the contest started.
Sorry but you are wrong !
In that contest, many of people had a wrong algorithm for first type of problem and got accepted ! (when problem changed, they algorithm became correct)
It's interesting that I understood the problem correctly. I remember that one, choosing "some" didn't make sense to me based on something (samples? problem difficulty?), so I chose the best meaning I could find at the spur of the moment.
Problem reading skills are also part of competitive programming skills. Trying to open problems early on or being given a random advantage by the contest system are not skills at all.
yeah i remember that contest!
i wrongly interpreted the original (incorrect) problem as though it was the modified (correct) one, and got AC! :D
I got the prompt from codeforces stating that the contest has begun and I clicked ok which took me to problem A. So did I get those extra 4 minutes or not?
Well, I also got it, but only in the regular time. So probably not.
Here is the email I just got :) ________________________________________________________________________________________________
Hello, VeniVidiVici.
The final contest of Coder-Strike 2014 will be started soon! Top highschool children from Moscow will meet in the CROC office.
Codeforces will host online rounds based on problems of Coder-Strike 2014 Finals.
I'm glad to invite you to take part in Coder-Strike 2014 — Finals. Actually it will be two separate online rounds: for Div. 1 and Div. 2. It starts on Tuesday, April, 22, 2014 12:00 (UTC). The contest duration is 2 hours. The allowed programming languages are C/C++, Pascal, Java, C#, Python, Ruby, PHP, Haskell, Scala, OCaml, Go, D and JavaScript.
It will be rated events for all the participants. Do not miss the round!
The round will be held on the rules of Codeforces, so read the rules (here and here) beforehand.
Want to compete? Do not forget to register for the contest and check your handle on the registrants page. The registration will be closed 5 minutes before the contest.
If you have any questions, please feel free to ask me on the pages of Codeforces. If you no longer wish to receive these emails, click — to unsubscribe.
Coder-Strike Team ________________________________________________________________________________________________
This might have been a little late :P
I think so...I receive the email just now...
relevant blog
Пришло письмо:
Внимание: начало раунда — 22 апреля (вторник), 2014 16:00 (Московское время).
Добрый день, dkirienko.
Совсем скоро стартует финал чемпионата Coder-Strike 2014! Лучшие школьники Москвы встретятся в офисе КРОК.
Codeforces проводит открытые онлайн-раунды по мотивам задач Финала. Онлайн-раунды разделяются по дивизионам участников, один из них будет для участников из Div. 1, а другой для участников из Div. 2.
Старт запланирован на 22 апреля (вторник), 2014 16:00 (Московское время). Продолжительность соревнования — 2 часа. Допустимые языки C/C++, Pascal, Java, C#, Python, Ruby, PHP, Haskell, Scala, OCaml, Go, D и JavaScript.
Все раунды будут рейтинговыми. Не упустите возможность участия!
Ну и т.д.
А теперь смотрим заголовки письма:
Date: Tue, 22 Apr 2014 19:21:47 +0400 (MSK)
From: Codeforces@codeforces.com
Очень своевременно!
То же самое, письмо пришло в 20:42.
Why there is no virtual participation?
unrated?怎么还不更新啊T_T
Post have been edited:
UPD. System was a bit sleepy and went to sleep. Maybe tomorrow it will update ratings. Have a good night!
:D
:)))
When is this contest going to be rated? There is no update in the blog post and no one has said anything. More than an hour has passed since the system testing phase has ended! Any idea?
Блин, рейтинг уже обновили, а дорешки всё нет)
Ну что вам, жалко чтоль?)
At least for me the ratings are updated — I join the ranks of the first division today!
Ratings have been updated. Got +132!!!!
1948->1894...the numbers is the same,but the order of them is different...Good night Codeforces.
at me it remained exactly the same: 1700 is that really the correct rating or is there a problem?
It means you do just the same as the system predicted according your rating during the contest...
ok thx. a little weird though
Wow!!!
Two consecutive 1700 as rating!
Really cool :)
what makes it even cooler is that 1700 is exactly the border of Div-1 and Div-2!
Nice problem statements.Easy to understand...
I can't solve 2day's problems after the contest !
Решал задачи, но в результатах отсутствую. Это только у меня?
Откройте дорешку демоны!
Издеваются(
Открылась дорешка.
Каким-то образом в архиве задача "Баг в коде" расплодилась и доступна в двух экземплярах.
Это норм для багов.
I haven't understood the problem Div1 B's Sample.
For Sample #4:
3 is an output.
For sample #5:
why 2 is not an output ?
Because 2 must be in the chat while 1 is in.
For sample #4 for it will be these, right?
3 is not always present ? right ? so how come 3 is an output for sample 4
We have no information for 5 and 2, so they can totally be absent all the time. When that happens, the 3rd slot have 0 present member and hence not counted for checking.
We must consider the following case.
Got it thanks.. :)
How to solve Problem C? (Div2 — Online Meeting)
I think explanation above inspiring enough.
will there be any editorial published for this round?
EDIT: it's now published. here is the link. :)