Codeforcesの皆さん、こんにちは!(Hello, Codeforces!)

I'm glad to invite you to my first contest, Codeforces Round #654 (Div. 2) which will be held on Jul/01/2020 16:35 (Moscow time) (notice **earlier time** than usual). All of the problems were mainly written and prepared by me. The round is **rated if your rating is strictly less than 2100**.

You will be given **6 problems** (one problem has a subtask) and **2 hours** to solve them. Please, read all the problems.

I would really like to thank:

- isaf27 for amazing coordinating my round.
- 300iq , alireza_kaviani , AmShZ , antontrygubO_o , dorijanlendvaj , lucky_21 , Monogon , noobiesAG , GrandDaddy and zxyl for mighty testing the problems.
- MikeMirzayanov for marvelous Codeforces and Polygon platforms.

The scoring distribution will be announced later.

Good luck, have fun and wish your high ratings :)

UPD: Scoring distribution : $$$500 - 1000 - 1250 - 1500 - (1500 + 1250) - 3000$$$

UPD: Editorial is out

Auto comment: topic has been updated by physics0523 (previous revision, new revision, compare).Thanks for all of these frequent rounds!

I hate Physics. Hopefully no problem related to physics!

Oh god, you read me! I'm afraid of this.

Even though I love Physics , I still hope there will be no physics related problems. XD.

same here pal.XD

I think Physics problems would be easier than the problems in this round

Good luck on your maiden round!

As a tester, I can say that the problems are really interesting and hopefully you will enjoy solving them :)

I dont know why testers are commenting a lot just for upvotes!? The only thing you done is you participated in a contest few days before most of the people and i dont see anything special to upvote u!

Nah this isn't the only special thing about testers.

He also left one rated contest so that others can enjoy one round.

Down voted, it's not true about many testers, you can't even understand how hard being a

goodtester is.P.S. I feel personally attacked. =(

Oh my god! Ok i upvoted you becuase its the only thing you want :( and its you third time you are editing your comment to dont get downvote!

What is wrong with you, I want you to understand how important testers are, some of testers duties are :

They should try submitting heuristics/wrong solutions, to make sure tests are strong enough.

They should help problem setters to replace the problems if needed.

They should write many different solutions for a single problem(if needed), to make sure unintended solutions that are wrong or are slow wont pass.

Doing many other things to make sure tests are strong, problems are not spoiled, statements are clear, pretests are fine and etc.

I saw that your comment has many upvotes, so it probably means many people don't know about testers, so I wrote this to show you how being a

goodtester is , not for upvotes.P.S. I enjoy editing my comments, you cant blame me for that.

Upvoted as i said

Thanks for upvoting. :)

Agreed. A good contest is the result of hardwork and collaboration of all testers, problem setters and coordinators.

I would like to thank all of you for making so many good contests for us.

Hope to have fun in this contest too:)

All the best to all!

As a tester, I can confirm that we do absolutely nothing in a grand conspiracy to gain contribution points by making meaningless confirmations on the contest announcement.

Yes, we can all see that.

As a non-tester who would very much like to become one, how can I get in on this conspiracy?

Just pretend you're a tester in the comment section, then they'll add you to the tester list in the announcement.

I love it when people compose formal responses to jokes.

this is what all testers say about their rounds:))

Wait for the next Global round. :)

For spoilers about tester comments of next Global join AC.

Scam

Proof of a conspiracy theory by testers to gain contribution.

Frequent comments like these is why nobody takes such comments seriously now!

If you found the questions interesting, you are clearly lying and spamming for contribution. As simple as that.

Or maybe they simply should be banned of the tester position as they have a much different taste for problems than the CodeForces community does.

Did some comments disappear? I think I saw few other replies to this comment yesterday.

Yes, nima_oof_che_mamehaii's reply disappeared, and all of the replies to it with it.

Do you think this is intentional or some other bug in the Codeforces website?

Probably intentional.

Yes,It's intentional..After many negative vote some commment filter out.I think this feature added from past 2 contest ..I think it's a good initiative.

Yes. They tried to silence me revealing the secrets about the tester-contribution conspiracy.

Hi i forgot to reply your message when my comments was there. you replied me that you and lots of testers didnt do it! And im gonna say yes! I agree and i was saying some of them are doing it in every single contest and i was replied to tester i think that its not fair! I dont realy care about upvotes and downvites i just say something that i believe so im sory if any one get mad at me becuase if those comments but im saying that these kind of works are not cool :(

I agree with that, but I'm not one of them, I joke about those things sometimes, but I really don't mind.

Codeforces should have option of downvoting comment even after upvoting it.

You can still downvote the comment next to that one.

I was master when I tested the round, I wouldn't have done it if I knew I would have missed such a great round :((

Great round????

scam

xD

What is the meaning of subtask? Does this mean a problem will have an easy and a hard version?

Yes

So are the 6 problems inclusive of the subtask (meaning there are actually only 5 distinct questions)or does it make it 7 to solve totally?

Should i know that? :/

Sorry, for some reason I just assumed you were a tester.

the latter one :)

6 distinct problems

Glad not seeing comment section filled with memes this time

May be someone is still trying to make new memes! :)

Good luck everyone. This community is insane lol

Here I was wondering why there were so many negative feedbacks until I saw the revision history XD

I just said I loved physics and people got offended, so had to change. I still don't know the reason

Nobody's got offended, and nobody cares whether you love physics or hate it.

Its not necessarily that people are offended. They might not agree with your opinion and hence the negative feedback.

頑張って皆！Good luck everyone!

I love Japan and the Japanese so i'm excited for contest :D

High possibility of involving anime characters

(one problem has a subtask)this seemsin-ter-uh-stingHope , we will see Geometry related problem.

I think you're looking for a negative response!!

Thank you for clarify.

Even geometry is better than problem B statement .

Exactly!!

Looking forward to this round!

Physics is evrywhere :v

Not in this contest plz

My UI of codeforces has been shifted to left side and I'm unable to see users and search problems with specific rating, Is there anyone facing the same issue since morning?

Try to click on desktop version on bottom of page

Ohhh! thank you for the help.

well all the testers can anyone just give slightest of hints as to what type of problemset is coming our way tommorrow

What do you think their replies would be ...other than "Some Interesting Problems".

but still it would be much better if we get to know type of problems.maybe tiniest of clues

"maybe tiniest of clues"Idk why.. but this sounds so-fuccin-funny..

their*

Generally testers don't give that kind of hints before contest..

Sure. I was a tester. I can tell you. The problems are interesting. Have fun!

We knew that.. 2 tester already told that.

GrandDaddy yeah xD

scam

I'll give you a hint for the next 100 rounds, I know, even better. You'll see greedy, constructive, more greedy, elementary math, guesswork, and greedy. You only have a chance at an actual cs problem if you can make it to the last problem, otherwise you'll write 20 lines of code since people on a platform called "code"forces do not enjoy coding.

Let me guess, F is your favourite problem in the contest?

I'm too dumb to get to it. But I saw by your comment you thought it wasn't great ig :(

But i'd rather code 30m for boring problem (though it is probably not boring for me) than not code at all. So probably.

Highly disagree. There's a fair amount of regular coding at a regular software engineering job. There are tons of "put a twist on a standard CS algorithm"-type problems on Leetcode.

This is the only place with such a high ratio of actual problem solving / lines of code. Let's keep it that way.

This contest wasn't the best one, but not because the implementations happened to be short. There are plenty of other contests with problems with similarly short implementations but that were nonetheless elegant and delightful.

I agree not many problems related to Binary Search, Graphs Algorithm etc. nowadays....

is it unrated?

It is rated if your rating is strictly less than 2100 !!

The answer is both a yes and a no.

(Did you read the announcement?)

Dude loves physics so much, he used it as his username, pretty sure some physics related questions,any ways good to have frequent rounds.

And if tourist were the problem setter you would expect problems themed around sightseeing tours.

Add the scoring distribution. If you can solve all the problems in a moment, you'll achieve exactly 10000 pts!

Auto comment: topic has been updated by physics0523 (previous revision, new revision, compare).All the best and hoping for a great round!!

Thank you for these frequent contests. we keep on learning and testing our skills it's really helpful

Do we need to practice HC Verma or Irodov?

This Comment is Deleted Due to negative feed back, don't know why but my comments are getting down votes all the time, even though the content of my comments are genuine & accurate. From now on I decide to never give any suggestion to anybody on codeforces in the form of comments , because I may not be intelligent enough to give suggestions to most of you.

thanks!

Dude, it is a pun on the problem setter username

It's a joke, not a pun.

I have participated in the writer's contests on another platform (Hackerrank), and his problems are always well-prepared and fun to solve.

I believe this round is going to be great as well!

Do you have a link to his contest(s) there?

Check This.. it's writer is physics0523 .

Here is the link to his latest contest.

Unfortunately problem statements are written only in Japanese, but the problems are like the ones from AtCoder Beginner Contest.

Are the problem statements shorter? physics0523

A contest a day keeps the pressure away.

* covid-19what's the meaning of (1500 + 1250) in scoring distribution for 5th problem ? can't we just write 2750 instead? Thanks in advance !!!

This means there will be 1 problem with two subtasks.

oh.. Now I got it !

Hope these long queues will be solved as fast as possible. And we will have good contest.

And it is solved :) when i returned to submit the problem after writing comment, it was solved.

I'm a beginner in CP and became PUPIL in last DIV 3 contest solving 4 problems. Hoping to do well in this contest too. But the problem I'm facing is I'm able to solve A, B in div 2 but on C I always get stuck. So any suggestions how to cover this gap between B and C?

I think the only thing you need , is "practice" .I also in your level & stuck on C.

Yes, I am practicing a lot. And when I see solutions of C then most of the time I find a new concept which I don't know and then I try to learn that from youtube or from somewhere else.

[deleted]

2 hours remaining to start the round. But wrong division cases on Codeforces Round #653 (Div. 3) is not fixed yet. Some experts get their rating changed. Will it be fixed before the round starts?

Maybe they registered for div3 round before they became expert.So they were not out of competition.

Yes i know that. But as far i know mike fixes it manually at the time of rating change.

Who cares?! ))

Some expert may solve the round carelessly since the round is not rated for him. They might care about unwanted rating change.

making the start 25m later would be perfect!

Hope the contest will be as interesting as the score distribution .

I hope in this round

"in queue"will not be shown for longer timehow can someone become a tester .... i want to experience being a tester

Make Ashishgup your friend and then ask him the same.

i think he is kinda too busy to this sort of stuff if u know plzz tell me how to be a tester

Hlo Guys. I am new here. What is the meaning of score (1500 + 1250) of 5th question?

Two subtasks

Thanks!

Hope to become green

Me too

I don't like this round at all...

And why did Akari have to make the E1 problem difficult? She should have kept quiet. Damn these front bench kids!!

yes keep changing time by one hour. Great.

No offense to the round writers, but problem B needs to be proofread by a native or advanced English speaker.

Edit: To clarify, I think the problems are interesting as always, but the phrasing and typos make the problem difficult to read for someone not familiar with the idea of the problem.

I was just going to say this. If there are going to be any rounds in English, it is best they are authored properly. FFS!!

Russian statement wasn't great either.

Good-bye my rating!

Add me to that list. Hell, for all I know I'm gonna become a specialist.

Add me too!!

Very Bad round with 90% maths

If you call these problems math, show at least one round which isn't math

that's cause all cf rounds are too math based.

The first question was basic arithmetic, we can't complain. 2nd question required you to know sum of first n Natural numbers which was also not any tough maths. C was casework, D was pattern. Why are u complaining?

(pls correct me if I'm wrong somewhere)

Mathforces :(

It seems like I am the only one who liked the contest. ??? Feel free to downvote if you disliked it. IMHO it is a balanced contest and it is not that MathForces as some of you think.

I don't feel like it's a mathforces round at all. For me it's just easy problems with many corner cases and very unlikeable implementation. In C 4 i got WAs and my AC code is just 7 if statements

My solution has only 2 ifs.

For me it felt like mathhomeworkforces. I did not have any programming problem, it was all logic and E some formular.

Interesting problems, but Im too bad for them(

WTF is going on with this comment section? Round isn't over yet

b,c problems are real shit. worst ever problem set. All problems are observation based no logic and maths needed.

I hate this B why I can't solve it spent the whole time on it :(

I'm curious how the testers easily understood problem B and didn't they feel D is too easy for div2D??

I felt difficulty of in order B>C>D.

Hmmm, that looks impossible

soryy,that last one is 'D' instead of 'B'.

this contest was difficult for me

[Deleted]

Why, so that every time someone has a bad performance they can make the round unrated by uploading solutions?

The round is going to become unrated? :(

thank you man i am very angry and nervous because it was the first contest in which my rating would have increased by 150+ ... and then i come to know that there was some kind of cheating ....hmm i am very disappointed .... for credibility plz check my graph i have worked my ass off hmmmmmm...

No. That guy was livestreaming his solutions on youtube (from start ). But I'm honest and didn't visit the site and solved what i could myself.

I'm not saying that's what happened here. But I am saying that if you make a round unrated if there are cheaters, then every round will be unrated.

yeah that's true.

It was travisscott as it can be seen at 26:48.

That's why number of LOSERS solving problem E increased exponentially suddenly at a certain point of time!!

CF predictor shows -2 rating for me, damn if cheating happened like that, I'm happy with this rating xD

you might have used it when system tests are going on

In the video, only A, B and C were solved (and there were also two failed submissions on D).

Due to actions of some of these people whole community suffers.Something should be done against them so that this is not repeated.

The account in the video was of travisscott Action should be taken

probably a fake account. But plag testing should be done.

Even if someone has posted the solutions, please do not share that in comments so that others can see those too during the contest!

What is the pretest 2 for D?

Try with: 5 10 Output should be 0 11000 01100 00110 00011 10001

i see, how did you solve D

This problem is kind of similar to the popular N-Queens problem with some changes. I followed almost the same analogy, but I was a bit worried. And the solution got AC in the main tests! *_*

Oh, how I didn't get it. But how to implement it so?

My solution gives correct answer for this case but fails on pretest2:(

i tried to fill the grid diagonally and didn't realize this case

The contest was really impressive and fun.

ObservationForces

ConstructiveForces

Did I accidentally open Codechef today for the contest?

how would we know also are you blind?

Codeforces Rule #343: Ignore comments from unrated accounts

Codeforces Rule #434: Ignore comments from Master accounts registered 2 months ago

Irony is you are the one breaking that rule

^Sent from an unrated account that registered 9 hours ago...

I feel bad for the problem writers because of the people who posted the solution to the contest on youtube.

On an unrelated note: is the contest going to be unrated?

Plagiarism is checked I guess. So all those who copied will be anyway disqualified

Please look into it MikeMirzayanov physics0523

Even then, you still could've gotten the gist of the solution of the problem and simply rewrote the code with your own style. It's also extremely difficult (basically impossible) to check for plagiarism if you submit with another language.

Especially the first 3 problems were just math formulas which are very hard to be checked for plagiarism.

We found the cheater, too. If some users copied some solutions, the plagiarism checker will work.

I think the contest will be still rated because sadly there are always some cheaters.

Even He cheated with youtube live.But got +543 ..Cheating is easy now :v And my some friend copy and change some variable , not caught by checker ! Is plagiarism jokes ?

Don't count on that. it's very easy to beat Plagiarism testing of codeforces.

Dude, no offense but do you really think plagiarism will work in these ad-hoc type problems ? Both B and C are have simply 1 liner solution. How will plagiarism work in this case ?

I don't know if this was intended or not, but I literally solved problem B using the samples without thinking in the main problem.

I did that for A. :) Sample test cases clearly showed (n+1)/2 if one notices carefully.

Nice contest, easy D. I got pretest 9 failed for problem E1 anyone has a clue about that pretest

I think your code is giving wrong answer in test case: 1 5 9 Correct me if i am wrong.

oh. i got it .I was wrong.

This is not a valid input. p <= n.

it failed at 3 3

1 5 9

I was talking about D.

Yes, my code failed at this test case. Thanks buddy

How to solve D? Greed- fill diagonally then it's left and right diagonal and so on...is giving wrong

the idea is ok but when you reach the cell (n-1,n) have to finish with the cell(1,n) and so on (apply modulo when you reach n)

Try 1 3 6

Your code will return 4 110 111 011

while it should return as mentioned: 0 110 011 101

My code gave output 0 yet didnt pass pretest 2

Was C really just casework? (that's how I did it but..). I hate such questions, wastes time, and morale. Couldn't solve D due to it :(

My observation was that it's always optimal to put all the type 2 people first. The reasoning is that since they always take from the smaller pile, then the size of the pile they'll take from will be $$$x, x-1, x-2, ...$$$ (if $$$x$$$ is the original size of the smaller pile). The larger pile will never be taken by the type 2 people until its size is less than or equal to the size of the smaller pile, resulting the continuation of the sequence. Hence it's never better to put type 1 people first.

The yes condition ends up being

`a+b >= n+m && min(a, b) >= m`

.That's it? 1 line of code. I tried caseworking and failed miserably.

same here wasted lot of time

I solved B completely based on the sample cases. I have no idea what does the problem say! I just make it work on samples, I do not know if I am gonna pass system tests or not.

anyways, thanks for the round authors and testers.

can someone tell me why my E1 solution fails at pretest 9 ?

try

3 3

1 5 9

what the solution for E without the f(x) and prime thing

i mean if the problem was just how to find number of permutation?

How to solve E1 ? Can someone point me my mistakes ?

I think your mistake is in these lines

You only need to iterate to

`mx`

. That's enough. So basically erase these linesYes, removing it give me

`AC`

, how stupid I was. Thansk for pointing out my mistakesIn problem B, The picture in sample test case changed during the contest. Initially there were only 3 green ticks. At the end of the contest, there were 6. This created confusion.

Proof-

During contest-Link

When I saw after the contest-Link

Yes. The green ticks confused me (no matter how many they had). The clearest representation would be to group the pictures into 4 categories to show which ones are the same.

Yes u noticed tooo

Back to specialist, RIP rating -100 :(

back to pupil,-127 :( all because of that problem B statement

Understanding problem B's statement alone should be rewarded with +50 rating

gimme that rating, I understood the problem in one go. (cuz i read it too slow)

I usually don't comment on the quality of rounds, but I think this round was really bad. A — C are just formulas and cases, and D is constructive. You literally could know zero algoritms, even not know binsearch and sorting, and still solve A — D, and this is really bad in my opinion.

First time I solved 4th, Thanks physics0523, you also gave the overflow details in testcase, thanks for that too, Last time I wasn't able to solve due to overflow.

Can anyone explain why submission no. 85677436 for problem B of this contest is wrong? While solutions with similar code are accepted.

I used floor((n-1)/2) + 1 as my answer but this failed on pretest 3. I wonder why? Even in the editorial, same solution is mentioned. I give (n-1)/2 + 1 it passes. Where is the mistake?

return type of floor is a double type. So if the returned value is large it will be printed in scientific notation (like 5e+008). where as when you do (n-1)/2 the result will remain an integer type and all its digits will be printed as normal integer.

F: Think for 0.2 seconds and implement for 30 minutes. What an amazing problem.

Weird template but ok

rip

Most Ad-hoc round I have ever given on CF.

A difficult contest compared to last few div2 contests.

Problem B was written terribly and also sample explantions were really bad. I won't say that the round should be unrated but it was one of the worst rounds by far in terms of problem statements.

Misunderstood the problem and wasted a lot of time. RIP rating

RIP English first... The diagrams were so confusing I just guessed formulas and hoped to get one that works.

Totally agree. Things were terribly written in the problem B. Was the problem B made to check English and patience of people? One-liner formula was the answer after reading the worst problem statement.

Exactly. What the hell did the green ticks mean ? He could have simply showed the correct 4 out of 6 in green ticks if at all that's what the author wanted to show. I was scratching my head for 10 min over that.

yeah, ticks just messed up the statement further

Boring contest

I hope that someone will have a good proof that why it was optimal to start with type 2 People in Problem C ! I am not able to reason it out! why Starting with Type 1 people is not optimal !

My logic was that you can shove your unwanted cookies at type 1 at the end, and they'll eat anything.

So, you should give your rarer cookies to type 2 people first

Its because type 1 people always chooses the cookie which is left MORE so they will never get angry if a cookie is left no matter v or c. Type 2 people choose the cookie which is left LESS so they will get angry if the cookie which is left less is finished. Attaching my code for your reference https://codeforces.com/contest/1371/submission/85648596.

i understand the idea ! But during the thought process I had in my mind that during all this If we feed all the TYPE 2 people first their will come a time where The ratio of cookies will reverse ! And That can happen quite some times during this procedure how to deal with it ?

Type 2 people are sadists they will try to eat up the cookies which are already less. So the number of both the cookies should at least be equal to the no of type2 ppl. The ratio won't reverse as type 2 will go on consuming the less cookies making it lesser.

Type 2 people consume the cookies that are minimum in number. Suppose you reach a state where both cookies are equal and you have only type 1 people left : then they keep consuming alternatively till both become zero. But the type 2 people consumption is skewed. Since they keep consuming the lowest available cookies, they will run out of the cookies if (min(a,b) < num(type 2 people)). So I wouldn't start with type 1 because they are agnostic of either chocolate cookies or vanilla cookies. They keep consuming. But type 2 nope they see which is lowest.

What was B? I didn't even go further after reading 4 lines. Highly unclear. Problems must be easy to understand but hard to solve. Seems this was reversed.

.

What cheating happened ?

.

Its a request to make the round unrated. Worst Problem statements, Lengthy, confusing Adhoc Problems, Round full of

cheating. Though my rating is getting a +45, but I don't care, because the round was terrible.no

B was like 5 lines of code wrapped in a ambiguous and confusing problem statement.

For question E, I have a claim that the answers are consecutive if there exists any. Can I ask for a proof / disproof of this claim?

Suppose that $$$x$$$ is the smallest positive number where f(x) is greater than 0 (In other words, $$$x$$$ is the smallest possible amount of candies you need to start with so you can beat all the opponents).

Suppose that $$$y$$$ is the smallest positive number such that if you start with Y candies, then at some point of time, You'll be able to fight at least $$$p$$$ opponents and win.

The answer lies between [x,y-1] inclusively.

for any $$$z$$$ < $$$x$$$ has f(z) = 0, so divisible by p, so [0,X-1] is totally unacceptable answer

anything greater than or equal to $$$y$$$ has f(z) = k * p, which is divisible by p , so [Y,infinity] is also unacceptable answer

actually, imo proving $$$f(z) = kp$$$ for $$$z \geq y$$$ is not trivial

But it's trivial to prove that $$$f(z) = kp$$$ for $$$z \ge 10^9$$$. Since, $$$f(z) = n!$$$ and given that $$$p \le n$$$, $$$f(z) \mod p = 0$$$

$$$y$$$ is always $$$\leq 10^9$$$

let $$$g(i)$$$ be the number of possible choices of $$$P[i]$$$ ($$$1$$$-indexed) for some $$$x$$$

you can prove that $$$g(i)$$$ is the same for any valid prefix $$$[1, i - 1]$$$ of $$$P$$$

obviously the number of permutations is the product of all $$$g(i)$$$

you know that $$$g(n) \leq 1$$$ (since only 1 integer remains), $$$g(i) \geq g(i - 1) - 1$$$ (because you can still choose all the indices that were valid for the position $$$i - 1$$$, except $$$P[i - 1]$$$)

so the values assumed by $$$g$$$ are consecutive, and if an $$$i$$$ such that $$$g(i) \geq p$$$ exists, a $$$j$$$ such that $$$g(j) = p$$$ also exists

an $$$x$$$ isn't valid if there is some $$$i$$$ such that either $$$g(i) = 0$$$ or $$$g(i) = p$$$

let $$$l$$$ be the maximum $$$x$$$ such that a $$$g(i) = 0$$$ exists, for $$$x' < x$$$, $$$g(i) = 0$$$

let $$$r$$$ be the minimum $$$x$$$ such that a $$$g(i) = p$$$ exists; for $$$x' > x$$$, $$$g(i) \geq p$$$, so there is some $$$j$$$ such that $$$g(j) = p$$$

so the only valid answers are in the interval $$$[l, r - 1]$$$

these values are all valid because $$$l$$$ is maximum and $$$r$$$ is minimum

Proof by AC: 85713453 (find minimum value in easy O(N), binary search to find the max value that works, print every number in between).

Will update with my "proof" later.

Proof:

Claim: f(x) can be written as some factorial, lets call it X!, multiplied by some mumbers <=X.$$$f(x)$$$ is divisible by all primes $$$<= X$$$ and not divisible by any primes $$$> X$$$, where $$$X$$$ is the number of possibilities of the index with the most possibilities.$$$X_a \le X_b$$$ for all $$$a < b$$$. This is because having a greater value of x in f(x) will never result in less possibilities for any position.It is ironical that someone who has physics in his username loves math!!!

it's not ironical.

Physics is just spicy math.

physics0523 write code for problem F. then he write problem for his code

Such a shitty round.

Terrible legends to problems, most of the time was spent on understanding the statesment((

yes bcoz of this I wasted more than 1 hour on 2nd question and this made this round very bad for me

A lot of Observational questions. If it hits , you could get AC in 5 mins, otherwise many kept scratching, like me.

Accurately put. That's exactly how it was. Hit the idea or hit the right youtube link. XD

I'm pretty bad at

`Observational`

questions. Is there any tag related to such problems? I want to solve them. Problem like problem C, I mean.Worst contest ever :/

logic in Problem D is the same as this problem from recent div3 contest

https://codeforces.com/contest/1360/problem/G

Can someone explain to me the solution to A? I used n / 2 with ceil.

ans = n / 2 + n % 2, because if n is odd, then we have 1 + (n — 1), 2 + (n — 2) ... n

or simply just (n+1)/2 as languages round down during division.

print each test-case output in newline.

Use ceil(n*1.0/2) it will work

In your case, you are using n/2 which will be treated as

intand to make it float multiply it with 1.0if n=5 your answer will be ceil(5/2)=ceil(2)=2

but it should be 3 as ceil(5*1.0/2)=ceil(2.5)=3

n was declared as float. I used ceil(n/2.0).

float can't accurately represent all numbers up to 10^9. Needs to be double or done via integer maths.

ohhh, ok thanks

you are printing all answers in same line

print them in different lines

cout<<ceil(n/2.0)<<endl; //use this

Question B was not clear. In the first sample test case,they should have clarified that the 4th and 5th picture are also same (they have different r thats why they should be different). Wasted more than 1 hour on it (I figured the formula in 2minutes) and could not touch C and D properly. Plz,clarify these things.Even on asking the jury ,it said only the last picture(for 1st sample test case) is not considered but actually the last 3 pictures were not considered in the answer.

I hope Editorial has some brilliant solution for F. Otherwise it is one of the worst problems I've seen in a while.

I guess it will be hard to believe the testers that comment "problems are very interesting" after this round:(

Very good round!

I think that it is in a sarcastic way!

The first three tasks were really easy. But I misunderstood the second task, and because of this I passed it at the 65th minute. If I would immediately understand the second task, then I would solve it much earlier and, possibly, would pass the 3rd task. :(

Some of the shortest code for A-C that I've seen...

A:

`(n+1)/2`

B:

`r >= n ? (n*(n-1)/2 + 1) : (r*(r+1)/2)`

C:

`(a+b < n+m || min(a, b) < m) ? "No" : "Yes"`

please can you explain the solution of B and C,

B: When $$$n > k$$$, then there are $$$k$$$ different patterns, one starting at each different day of the week. When $$$n \le k$$$, you only have the straight line pattern. So for $$$r \ge n$$$, you get $$$1+2+...+(n-1) + 1$$$. For $$$r < n$$$ there will never be enough days in the week for a straight line, so it's $$$1+2+...+r$$$.

C: The observation was that it's always optimal to put all the type 2 people first. The reasoning is that since they always take from the smaller pile, then the size of the pile they'll take from will be $$$x,x−1,x−2,...$$$ (if $$$x$$$ is the original size of the smaller pile). The larger pile will never be taken by the type 2 people until its size is less than or equal to the size of the smaller pile, resulting the continuation of the sequence. Type 1 people always take from the larger pile, so you'll only fail if you run out of cookies. Hence it's never better to put type 1 people first. You also need to check if there are enough total cookies for all the guests.

This should be the editorial for C

Include D as well :XD

B should be

`(r*(r+1)/2)`

, isn't it? Typo?Oops you're right, fixed.

Any idea what does TC4 in E1 looks like?

Problem B is absolute trash, super unclear, and boring.

Problem C isn't better. Author, can you tell me what the interesting idea or approach is behind this problem? As for me, it's just about understanding problem statements and implementing stupid case analysis.

You know, >75% of participants solve only A, B, and C. So for them it was a 100% shitty round.

P.S. please never invite AmShZ and noobiesAG as testers anymore, if they find this round "really interesting" and "such a great".

Solved A in 3 mins from then till now I am unable to cracks B's statement If B & C problems are like that how would anyone solve any on Div 2

Even A,B,C Solution found on youtube after 1 hours+ . Link. Please notice .MikeMirzayanov ..Please find all the cheaters or and if not possible hope this contest will be unrated.I know to make a contest, authors made so hard work,, But It is unfair someone copy the solution and take positive rating before our eyes And someone go down for only cheaters and gain negative rating . .

**N.B: I was not submit any solution cause busy sometimes on the contest time.Now i feel good cause some problem statement was unclear too , specially B..the contest was worst overall.

It's impossible to catch cheaters. The first three problems are a simple formula so you can rewrite it however you want. In addition, many people were confused by the problem statement for B. Many questions were asked with disappointing responses. The problems were of really low quality so many people who usually solved the first 3 questions couldn't even solve 2! This would cause the cheaters to get a lot of positive rating change which is clearly unfair to the community. Thus, I think that we should make this round unrated.

Yes the jury was badd

Listen to the community: looking at the comments I can find only 2 which say that they enjoyed the contest (not including testers who apparently have a different taste of problems than we do). Clearly, the contest is disappointing to a lot of people. This can be shown by the contribution of this blog. 5 minutes ago it was at 713 and now it is 683. I think that this round should be

unratedIts correct.Cheaters solved a,b,c easily.and someone can't solved B with their hard work. So By result cheaters got positive rating and hard worker got negative rating . It's unfair (

i solved e2 but i didn t understand problem b:))

Wow, Problem F is really constructive. Are there any easy solutions to F? I tried to implement the Segment Tree, but it is too hard (at least in my case)

B should have tag unreadbale instead of math.

The statement for B was very confusing.For the whole contest, I thought that every week that divides the total number of days given, results only in one pattern.

So beneficial a round to SegTree-addicts.

Thanks for writing the round OP. I hope you don't take the hate comments too personally. I especially liked problem E, thought it was a very neat way of combining primes factorization with sorting/arrays