I don't want problems like today's C to get normalized

IOI selection has not concluded yet please don’t spread misinformation.

This statement is.

Fun fact: the setter has solved 4000+ problems on codeforces and 10k+ problems on a Chinese online judge(which provide the remote judge service of codeforces and atcoder). I'm so shocked by his hard work.

This statement is true.

This statement is false

Thank god I'm unrated

All of these statements are false

Upvoted both the blog and this comment. Luckily no one hate CMs.

D can be solved in O(n): 263368704

why

This statement is false

I proved that the required upper bound is $$$O(N / \log N)$$$, but because creating a test case that achieves that upper bound also seemed non-trivial, I didn't seriously consider the constant factor. I ended up submitting with a slightly conservative estimate, taking into account the possibility of tight TL or ML. (Also, since the pretest succeeded with a limit of 1K, I submitted with a limit of 2K.)

While it might have been better to have some cases in the pretests closer to optimality, I think it's great that there were test cases in the system tests that required quite large upper bounds. Thanks for preparing a good contest!

wtf is this comment spam??

sto bnxe orz

An even number of the above statements are true iff the next statement is true.

I will elaborate on that.

You're right, it wasn't expected and that's mostly my fault -- I was able to come up with $$$O(n^2)$$$ solution pretty easily and thought that a lot of people will think about solution $$$O(n \cdot bound)$$$ after some time. In general, I don't want for last problem to be that hard and I will try to listen to feedback of other people more carefully. I still hope that people had fun thinking about this problem (and others problem of the round).

And one more point -- we intentionally didn't put in pretests tests where you need to use very big value of bound (maximum one that zltzlt was able to construct was around 3k and you can pass pretests with around 1k). I also want to elaborate on that. In general, I would vote for pretests to be as strong as possible, but here it was kinda special -- we didn't want people to try to squeeze solutions just with pure guessing (and since I've underestimated the problem, I thought that a lot of people will try to do so), that's why I agreed to not use such tests into pretests. In retrospect, I would insist on putting them (because problem already turned out to be too hard), and I fell sorry for maspy, congratulations on the win though!

IOI selection has not concluded yet please don’t spread misinformation.

The statement is undecidable.

sto bnxe orz

sto bnxe orz

sto bnxe orz

sto bnxe orz

It seems people will make accusations. I purposely avoided making any as I don't have evidence. I encourage others to not make potentially slanderous accusations without proper evidence.

For each of the statements above, either they are true or they are false.

sto bnxe orz

It wasn't fun at all

IOI selection has concluded already; please don’t spread misinformation.

I am a CP enjoyer, CF Master, IOI medalist, problem setter myself, and probably a member of the Serbian committee from next year

Am I the only one for who the contest page is broken? I can't read problem statements or watch standings or submit.

sto bnxe orz

Bruv, the "just give me your codeforces password" part was smart, it would've been over for them.

C has a significantly simpler $$$\mathcal O\left(n \log\left(n\right)\right)$$$ solution. Notice that instead of stopping at the LCA, if the path has missing entries, it is valid to continue farther up the tree. The path only has to stop when it runs out of missing entries or it reaches the root. Therefore, assuming at least one entry is not missing, a simple solution is to repeatedly choose the largest entry $$$x$$$ with missing neighbors and replace those missing neighbors with $$$\left\lfloor\frac x2\right\rfloor$$$ (or $$$2$$$ if $$$x = 1$$$). This can be implemented in about 20 lines with a priority queue:

int n;
cin >> n;
vector<int> A(n);
for (int &a : A)
	cin >> a;
if (*max_element(begin(A), end(A)) < 0)
	A[0] = 1;

priority_queue<pair<int, int>> Q;
for (int i = 0; i < n; i++)
	if (A[i] >= 0)
		Q.emplace(A[i], i);
while (!Q.empty())
{
	auto [a, i] = Q.top();
	Q.pop();
	if (i > 0 && A[i - 1] < 0)
		Q.emplace(A[i - 1] = a == 1 ? 2 : a / 2, i - 1);
	if (i < n - 1 && A[i + 1] < 0)
		Q.emplace(A[i + 1] = a == 1 ? 2 : a / 2, i + 1);
}

for (int i = 1; i < (int)size(A); i++)
	if (A[i] / 2 != A[i - 1] && A[i - 1] / 2 != A[i])
		A = {-1};
for (int a : A)
	cout << a << ' ';
cout << '\n';

Clearly, you are the second type of person.

I hate haters

most intelligent grey

I love the $$$O(\frac{n^2}{\ln n})$$$ solution of problem F, however I spent my whole time in $$$O(n\log n)$$$ overcomplicated segment tree merging solution and mixed indices like tr[x<<1](should be tr[tr[x].ls]) then finally finished 10 minutes after the contest...

edit: I got the first blood!! so funny XD

thank you for the contest. :)

I really enjoyed solving C today.

Said no one ever!

Stucked on C for $$$45$$$ minutes and finally got 1 place lower than sevlll777, who solved 1 problem less than me. The slowest episode ever.

Bad network

I've wasted about 30 minutes because of 502 and cloudflare

The long wait is over, and the ranking has been released.

May Luogu provide a English site just like atcoder?

purple sus

What the fuck of the C???????????

There are 10 types of people: 1. Those who like bit manipulation. 2. Those who don’t like it.

it forces you to "if else if else if else if else if else if else..."

He is spamming long texts in this thread, so that people loose interest while scrolling through this blog. He is probably among those cheaters.

It's called qq because when you try to register you cry

Use the among us trick to find the real IOI team

OMG, jiangly's stream!

It was more like Div. 1.5

Latin America, Argentina, Universidad Tecnológica Nacional — FRSF

Fruta Fresca 🍉🍋🍌🍍🍎

JPrime marianoferesin FedeNQ

problem C has quite a bit heavy implementation.

C's editorial is not friendly as a regular C. LCA is not something that most people thinking about in this position. There's still a solution without using such advanced topic, but why the author didn't do that?

Best wishes for everyone's A, B, C and D.

to give div2 people a harder problem to upsolve

I don't think ratism really a big thing, I think it's just the massive amount of glazing this community does for CMs, Masters, and Grand Masters.

https://codeforces.com/contest/1976/hacks/1028125

Is this hack not weird? Why would they randomly hardcode wrong answers. Seems like a trick by the hacker to gain points by hacking solutions like this.

no

Tough contest. We weren't given enough time.

when will the rating be updated ?

https://www.islamweb.net/ar/fatwa/211225/القذف-حكمه-أنواعه-وضابط-كل-نوع-وعقوبته

Uzbekistan's team:

• Asilbek Sunnatov (Sunnatov) — 2nd time at IOI, 1 attempt left

• Husanboy Mansuraliev (Husanboy) — 2nd time at IOI, 0 attempts left

• Ulugbek Rahmatullaev (heaven2808h) — 1st time at IOI, 2 attempts left

• Mardon Hazratov (MardonbekHazratov) — 1st time at IOI, 0 attempts left

Nice investigation!

A possible explanation:

Intelligence and having a girlfriend is perhaps positively correlated in the general population, but this doesn't mean that every subgroup of intelligent people have a lot of girlfriends.For instance, the subgroup of intelligent 7 year old boys. Very few of them have girlfriends compared to the subgroup of intelligent 25 year olds. Here age is positively or negatively correlated with having a girlfriend. So it always depends on the characteristics of the subgroup you are looking at.

At CodeForces, there is an obvious other correlate at play, namely nerdiness (basically, are you more interested in objects or people). Nerdy people tend to have fewer girlfriends in most cultures, at least until the age where they begin to make bank. And, among intelligent people, nerds will be more likely to end up at codeforces, because codeforces attract exactly the people who are interested in numbers and objects. (Saying this, this doesn't mean that nerds don't want social interactions, it's all relative.)

With regard to the correlation between intelligence and beauty, there is another explanation in addition to yours: That posive traits like height, beauty and intelligence are all possitively correlated with each other because they are all caused by the same thing, namely good health. Good health here especially means good nutrition in early childhood and no unfavorable genetic combinations. If this condition of "no malnutrition and no genetic defects" is satisfied, people will on average be more intelligent, more beautiful and taller than those people who grew up with malnutrition and genetic defects (genetic defects can manifest themselves in many ways, so they are likely to affect both facial symmetry and development as well as height and brain development).

Will queue issues appear in contest because of EDU 166 system testing?

Will there be delays due to an overlap with yesterday's Educational round's System Testing?

I'm officially having skill issue with constructive problems (again) :D

Good luck to Mongolia's team!

Solution :

Why? I enjoyed it.

if he is not lying about he's rating, then most probably he's account is funnylmao123, because there are only 13 1880 rated accounts on codeforces and it's the most suspicious one. I checked the contests of this account and most of A's was solved too late and it's the sign of that the person sends him ac code and he "modifys" it and it takes time, only a few time A was solved fast and these problems were too easy it means maybe he solved it in his own.

sto bnxe orz

If misinformation spreads this behavior, please cease you immediately.

Contest submissions should be prioritized over system tests.

Why i am still blue even my max rating has been changed to candidate master?

My post contest discussion stream for problems ABCDE

i don't want comments like this get normalized

The problems are quite suitable for Educational Round,I like this style.

I am 25 years old

need +1

but.. you didn't even give the contest?

"to beat a friend, makes it more interesting" — This is the most satisfying thing ^_____^

Look at the standings. It seems your F is too hard for a div2 so it works like a 5-problem round. Is that good?

look at the tester predictions, it is hard to be very accurate in predicting difficulties. F isnt very relevant for div2'ers anyways (only about 10 solve an average F?) that numbeer only decreased by 10.

Mongolia's team:

• Irmuun Chinbat (Irmuun.Ch) — 1st time at IOI, 1 attempt left

• Onolt Khurtsbilguun (Onolt_kh) — 2nd time at IOI, 0 attempt left

• Tamir Jamiyangarav (tamir1) — 1st time at IOI, 0 attempt left

• Erkhem Ganzorig (ezzzay) — 1st time at IOI, 2 attempt left

It could be that the cheater is actually out to "expose" high-rated users who sell out easily. OP made the right call here.

Using QQ is a terrible suggestion to someone who doesn't live in PRC and doesn't know Chinese. QQ-international is abandoned by tencent long ago and is not even supported on my device. When I tried to register in Play Store app, I got the following error message:

I tried to go here to register on a website, and it told me:

Your mobile phone number XXXXXXXXX is a security risk, please go to mobile QQ to register. If you haven't downloaded mobile QQ, scan the QR code below to download mobile QQ and register.

Then I had to download the app from https://im.qq.com/, because of course the version in Play store is outdated. Well, and after jumping all these hoops (and also passing Chinese CAPTCHA) I end up having this:

Meaning that they will not let me register with non-Chinese phone number no matter what, because I got the same error message on like 10 different days I tried to register over the last year. If you really want foreigners to get into Chinese IMs, at least suggest WeChat, it's somewhat possible to register and it actually has an English interface...

is carrot working for anyone?

I couldn't submit B for a long time cause cf wanted to verify if I am a human.

Woohooo, let's go! Onsites are back!

same

It might be better to swap the D and E.

I could not understand your solution very well. It sounds like a great idea. Can you please explain in more detail (possibly with your thinking approach). Thank you

Maybe you should ping the author chromate00 to check this.

It's quite fun seeing I am blue with the rating of 2007 :)

but I believe it will update soon.

The solution to problem D involves identifying a pair (i, j) that satisfies the following conditions: A[i-1] == A[j], A[j] != 0, and for every k in the range i <= k <= j, A[k] <= 2A[j]. Here, the array A is a prefix sum array derived by considering '(' as +1 and ')' as -1. To illustrate, consider the sequence "((((()))))".

Interestingly, while many have approached this problem with a time complexity ofO(n * log(n) * log(n)), there exists a more efficient solution. This problem can actually be solved inO(n) time 263375129

No because $$$3500-2500\ne2500-2000$$$ :)