Practice more div2Cs would be OK.

Try to solve them as quickly as you can.

C is just about implementation

Amazing idea!

In D You first notice that you must choose a prefix of pipes, because after $$$t$$$ seconds the amount of water is fixed when the number of pipes is fixed, and water can always flow from front to back.

Then you could just do it by binary search.

Remember to check the minimum time $$$t_0$$$ to fill all locks when all pipes are chosen. When $$$t \lt t_0$$$ binary search may tell you that there's a solution but in fact there isn't.

The last editorial of round that based on Russian olympics was extremely slow.

So I'm afraid that we should wait at most 3 days.

I don't think it's reasonable that there weren't constraints on $$$\sum n$$$ and $$$\sum m$$$. Some people (including me) used O(nT) initialization in each testcase, and some of them got hacked, some didn't.

My submission ran about 1300ms so it can't be hacked due to its relatively small constant, but some submissions that ran 1900+ms got hacked because of the fluctuation of the judge.

I don't think it is constant that matters in Codeforces contest. Maybe a TL of 1000ms is more preferable for C++.

Maybe there is some mysterious optimization in the implementation of std::vector. In fact I don't know, either.

Your solution is exactly $$$O(nT)$$$, and there isn't any constrant on $$$\sum n$$$.

The hacker generated a testdata with $$$t = 10000, n = m = k = 2\times 10^5, q = 20$$$ to maximize $$$\sum n$$$.

LIGHTNING EDITORIAL

THANK YOU SO MUCH FOR PROVIDING THE ROUND!

Very interesting problems.

Thank you writers, testers and coordinators so much!

It's correct, in fact.

Thanks!!! Feeling confused when trying to read the official editorial

Thank you for your effort anyway.

Can't wait to read the editorial

sorry but it's two days after the contest and there is still no editorial.

coue any one explain how to solve E2, please?

Just try to solve 3 problems in div 2 contest.

After the round read the editorial and solve D and E problems.

Keep doing this, then you can nearly always solve at least 3 problems in div2 contests.

You can be blue even purple then.

LONG STATEMENTS made bad reading experience.

A good contest anyway.

TOO LONG statements and quite bad experience on prob B

Solved A, B and C after 44 mins

Then sitted for nearly 2 hrs unable to solve D.

Felt so tired at midnight.

Huge difficulty gap between C and D.

And I hate weak pts.

I think you are right. I suppose it should be $$$\min\lbrace dp_{j + b_j}\rbrace + 1$$$, too.

but their difficulties are different so they aren't bad triples.

The problem statement says "at least one of the conditions are met"

I suppose that the time complexity of F should be $$$O(n2^n + A\log A)$$$ instead of $$$O(2^n + A\log A)$$$. (:

Could someone tell me if there are some mistakes?

There are many hacks on unordered_map and I suppose we should avoid using it in Codeforces contests. Here a blog written by neal showing how it works.

In your code, when it comes to nA += (ca[a[i]]-1) * (cb[b[i]]-1);, I suppose that it overflows the int limitation

They are hack just because they didn't use long long

Substract the illegal ways from all the ways.

There are in total $$$\dbinom n 3$$$ ways to choose $$$3$$$ elements among $$$n$$$ of them. Now considering how many of them are illegal, that is, none of the two conditions in the statement is satisfied.

To calculate it, we first define cnta[x] as how many times topic x has occured and cntb[x] as how many times difficulties y has occured.

Then assume that we choose the $$$i$$$ th problem, since no two problems share the same $$$a_i$$$ and $$$b_i$$$, we can assume the second problem we choose shares the same $$$a$$$ with $$$a_i$$$ and the third problem shares the same $$$b$$$ with $$$b_i$$$. So we just need to calculate 1ll * (cnta[a[i]] - 1) * (cntb[b[i] - 1]).

You can view my code 131440598 for more details.

Sorry for my poor English(

Thx for the fast editorial! :)

A, B and C are quite creative problems!

but I think D is quite a classic problem

E1 is a simple combinatorics but I can't solve E2 and F T_T

I tried but have found that it's quite hard to explain T_T. A hint is that if one says that someone is a crewmate, then they must be either crewmates or imposters.

Thus you can use union find set to deal with the problem, at last coloring a bi-graph is needed.

Elaborating the detail is far beyond me — my poor English but you can have a look at my code here

Yes and union find set is used to solve D

thx and I also did a very silly mistake(

ACed now

Me too, I was using a max heap too but also get a WA on test 5

Very good contest!! I think the problems are very fascinating and the time is friendly to Chinese participants.

However I didn't solve B very quickly and I think D is easier than C.

It's hard to come up with the construction without watching that video

Thx for the explaination and I also wonder how to bruteforce in $$$O(n^2)$$$

sorry but I can't figure out how $$$n \gt \sqrt{8\max a} + 2$$$ is calculated, could you please give an explaination?

It's 0 instead. Suppose Qingshan start at x = 2 (He can't start at x = 1 or x = 3 because he wouldn't be able to make the first move)，Then no matter which y Daniel chooses, Qingshan is definetely going to lose.

Chinese round!!! Chinese time!!! I can take part in the contest at school!!!

I used segment tree in D and it worked well. Just add new nodes dynamically so as not to get a TLE.