Hi!

Qualification round of the Yandex.Algorithm competition that will start on July 8, 2013, at 7 p.m. This round is virtual, so you need to start your qualification within 24 hours from the beginning of the qualification round. Qualification will last 100 minutes even if you will start at 6:59 p.m. Please, do not discuss the problems until 8:40 p.m. July 9 — someone can be still solving the problems.

The 2,000 best contestants who have solved at least one problem will advance to the elimination stage. Already advanced from test round participants will have a chance to work with the TCM/Time.

Good luck! Almost 200 t-shirts and more than half a million rubles are waiting for you!

**UPD:** Archive is at the competition site.

Qualification will last 100 minutes even if you will start at 6:59 p.m. Please, do not discuss the problems until 8:40 p.m. July 9 why same as start 4:00 p.m someone can be still solving the problems. You need not type did not :D

I did not understand

Is pascal allowed? because this is the only programming language that i can use.

I think that it is allowed.

Maybe I missed something, but how can you prevent someone from cheating, like, creating two accounts, opening the problems with one account, solving them, and then submitting them with the other account later?

This does not work, actually. The quota is 2k, you can write at most 5 different solution during the contest, so you can not make a significant impact on results.

We have a system that finds similar solutions and presents suspicious pairs of solutions to the judge.

No, I mean using the first account to read the problems in order to gain time advantage.

so true. Also, if you do bad in your allocated 100mins, you can just register a new account and try again. so basically, the qualification round is 24hrs.

Basically, most participants do not think about any cheating, cause that makes no sense — if u are not able to qualify to 2000 in fair manner, your chances to go to final are equal to 0.

Also, I suppose cheaters will be banned for good and all.

most participants do not think about any cheatingNot sure if you have ever organized online contests, but from my experience I can say that there will as many cheaters as rules will allow. And for this competition virtual contest seems like a poor idea. Why not make it 24 hour long contest like google does?

Just don't do it — it's that easy. Almost as easy as to go into the store and don't steal anything.

Good luck to everybody!

a

Sure, after round ends up. We hope to do it soon

a

How is the contest system supposed to work:

Right now I can see the results here: http://algorithm.contest.yandex.ru/contest/307/standings/?p=1

However when I log in it disappears.

Reported to developers. Thanks.

Update: atleast in current qualification standings will be open for everyone. For future qualifications/other virtual rounds possibility for everyone to see the standings will be discussed.

Yandex has a foul contest scheduling. Totally insane.

i support yandex! its a good encouragement for all.

(mistook in last comment)

They exposed themselves. Go home yandex, u r drunk!!

Dude, u may drunk I think!

By unliking this comments you guys are proving nothing went wrong. Huh!! Just for a t-shirt the insanity scale is rising above. Go on, we are being amused by this as more effectively as u unlike more.

How many problems are there in the contest? It would be very kind if you answer and only after that put a minus on this comment, because there are already 3 people who could answer me but they didn't.

6

Thanks, man)

Could you enable us to see the test cases, like in codeforces? If not, please put them for download (but ofcourse

afterthe contest ;) ). It would be very great if you did that! :) Thanks!all test data will be published after the contest

Archive is at the competition site

When I go to the link, it shows:

The URL you requested has been blocked. URL = invalid

Which link do you mean? http://algorithm.contest.yandex.com/ or the archive?

The archive.

That's strange. The link works perfectly for me, also works in the incognito mode. Can you visit disk.yandex.com?

i think my solution on problem B was better than one int the site; we know that k>=4 . if k>=4 and k^2=p1*p2+1 than k must be even and k-1 and k+1 must be primes. at first i use eratostenes sieve and than iterate (k=4;k<=n; k+=2;) if(k-1 and k+1 prime)print k;

please coment it's time complexity.

why is this if k>=4 and k^2=p1*p2+1 than k must be even and k-1 and k+1 must be primes,I dont understand the theorem you used.can you please explain...

IMHO, k^2=p1*p2+1 => k^2-1=p1*p2 => (k-1)*(k+1)=p1*p2 => (k-1)=p1, (k+1)=p2.

But it's wrong.UPD1: I was wrong.It isn't wrong. p1,p2 are prime so

k-1 = p1, k+1=p2 OR k-1=1, k + 1 = p1*p2 = 3 but that's impossible

It's correct.

There are 4 cases:

1) k — 1 = 1, k + 1 = p1 * p2 => k = 2 , p1 * p2 = 3 — impossible

2) k — 1 = p1 * p2 , k + 1 = 1 — impossible

3) k — 1 = p1 , k + 1 = p2

4) k — 1 = p2 , k + 1 = p1 — equal to 3)

You are right. I was wrong.

Will you make editorial as the test round you make a very good one? :)

I want to understand the C (Board Game), I have lot of try (I know the nim..) but my last try got TLE, so I download the solutions, but I didn't get it. The solution is very short, exists some short explanatation? (Or just should realize this pattern?)

UPD: Sorry my comment, I found the analysis .