Educational Codeforces Round 70 [Rated for Div. 2]
By awoo, history, 5 years ago, translation, In English

Hello Codeforces!

On Aug/07/2019 17:35 (Moscow time) Educational Codeforces Round 70 (Rated for Div. 2) will start.

Series of Educational Rounds continue being held as Harbour.Space University initiative! You can read the details about the cooperation between Harbour.Space University and Codeforces in the blog post.

This round will be rated for the participants with rating lower than 2100. It will be held on extended ICPC rules. The penalty for each incorrect submission until the submission with a full solution is 10 minutes. After the end of the contest you will have 12 hours to hack any solution you want. You will have access to copy any solution and test it locally.

You will be given 6 problems and 2 hours to solve them.

The problems were invented and prepared by Roman Roms Glazov, Adilbek adedalic Dalabaev, Vladimir vovuh Petrov, Ivan BledDest Androsov, Maksim Neon Mescheryakov and me. Also huge thanks to Mike MikeMirzayanov Mirzayanov for great systems Polygon and Codeforces.

Good luck to all participants!

UPD: Our friends at Harbour.Space also have a message for you:

Hello Codeforces!

Ready to get deep?

Take a minute and ask yourselves — what skills are I missing, that I would love to have? What are those key qualities that would take me from being a decent developer to an extraordinary one? Am I where I want to be, in terms of personal progress?

At Harbour.Space, we focus on the key technical and social requirements of the jobs of the future. Our three-week courses are designed for students to acquire and develop specific skills through seminars, workshops, projects, and case studies in a very short amount of time.

Mike Mirzayanov’s course, Advanced Algorithms and Data Structures, is a great example of this:

This, in combination with our unique academic environment, extensive professional network, and our seaside campus in the beautiful city of Barcelona, provides for a truly unique learning experience.

Interested?

Fill out the form below, get more information, and see how you can come attend Mike’s course to see what all the fuss is about!

APPLY HERE→

See you soon!

Harbour.Space

Congratulations to the winners:

Rank Competitor Problems Solved Penalty
1 CSWhisky 6 258
2 tfg 6 302
3 Sugar_fan 6 310
4 jiangly 6 338
5 Geothermal 5 195

109 successful hacks and 290 unsuccessful hacks were made in total!

And finally people who were the first to solve each problem:

Problem Competitor Penalty
A nantf 0:03
B Denverjin 0:11
C Geothermal 0:20
D dhxh 0:10
E lqs2015 0:19
F duxing201606 0:59

UPD: Editorial is out

  • Vote: I like it
  • -198
  • Vote: I do not like it

Comments Comments (196)
| Write comment?
»
5 years ago, # |
  Vote: I like it +46 Vote: I do not like it

I have joined 7 Educational Codeforces Round and 6 of them, my rating went up.So I love Educational Codeforces Round and I hope to become orange after this round.

→ Reply
  • »
    »
    5 years ago, # ^ |
      Vote: I like it +32 Vote: I do not like it

    Wish you good luck~.By the way,this group of people have held plenty of Educational Rounds and did help us a lot.Thanks to them~ :D

    → Reply
  • »
    »
    5 years ago, # ^ |
      Vote: I like it +9 Vote: I do not like it

    I have joined 3 Educational Codeforces Round and all of them , my rating went up . So I also love Educational Round and I hope to become purple after this round .

    Wish you good luck too~~

    → Reply
  • »
    »
    5 years ago, # ^ |
      Vote: I like it +9 Vote: I do not like it

    Wish you good luck(run away My rating went up to 1653 in my last Educational Codeforces Round.Wish I can come back to Expert in tonight's Educational Codeforces Round and wish all of you will have a good luck！

    → Reply
  • »
    »
    5 years ago, # ^ |
    ← Rev. 2   Vote: I like it +2 Vote: I do not like it

    I have joined 1 Educational Codeforces Round and in 1 of them, my rating went down. So I just hope to not become green after this round.

    2 days later.....

    o o f

    → Reply
  • »
    »
    5 years ago, # ^ |
      Vote: I like it +6 Vote: I do not like it

    So this edu round was kind of unexpected. How is your rating now?

    → Reply
    • »
      »
      »
      5 years ago, # ^ |
        Vote: I like it +9 Vote: I do not like it

      CF-Predictor says my rating can be 2101 after this round.

      → Reply
      • »
        »
        »
        »
        5 years ago, # ^ |
          Vote: I like it 0 Vote: I do not like it

        Kind of really close. Hope you will be orange ^^

        → Reply
    • »
      »
      »
      5 years ago, # ^ |
        Vote: I like it -9 Vote: I do not like it

      Mine's 1394. That just sucks.

      → Reply
»
5 years ago, # |
  Vote: I like it +23 Vote: I do not like it

We expect halyavin will be disappointed in this round.

→ Reply
»
5 years ago, # |
  Vote: I like it +9 Vote: I do not like it

good problem as usual

→ Reply
»
5 years ago, # |
  Vote: I like it 0 Vote: I do not like it

What is the difference between these Educational Rounds and others? I have never joined Educational Round :)

→ Reply
  • »
    »
    5 years ago, # ^ |
      Vote: I like it +4 Vote: I do not like it

    Educational Rounds are based on ACM/ICPC rules and there are 12 hours for hacking any solution you want after the contest ends.

    In traditional codeforces rounds,hacking is only avaliable during the contest and you can only hack the solutions written by coders who are in the same "Room" with you.Moreover,points of each problem decrease as time passes.

    → Reply
    • »
      »
      »
      5 years ago, # ^ |
        Vote: I like it 0 Vote: I do not like it

      Thanks for your reply, so these are beginner-friendly rounds :) What happens if I have been hacked? Do I lose any points or not?

      → Reply
      • »
        »
        »
        »
        5 years ago, # ^ |
          Vote: I like it 0 Vote: I do not like it

        It counts as a failed submission and you lose points

        → Reply
        • »
          »
          »
          »
          »
          5 years ago, # ^ |
            Vote: I like it 0 Vote: I do not like it

          Sooner or later, if my submission is incorrect (it may pass from pretest but fail on final test) it will already not pass from the final test. So, as far as I understood, this hacking stuff only brings points to contesters who use it.

          Thank you for your reply :)

          → Reply
          • »
            »
            »
            »
            »
            »
            5 years ago, # ^ |
            ← Rev. 3   Vote: I like it 0 Vote: I do not like it

            People don't gain points from hacking in educational rounds. Systests in educational rounds consists entirely of successful hacks as far as I know.

            Ranking in educational rounds is based on first the number of problems solved, and then the total time used for all the solved problems plus failed submission penalties.

            I wouldn't say educational rounds are more beginner friendly than regular Div 2 rounds.

            → Reply
  • »
    »
    5 years ago, # ^ |
      Vote: I like it -24 Vote: I do not like it

    No differences.

    → Reply
    • »
      »
      »
      5 years ago, # ^ |
        Vote: I like it +3 Vote: I do not like it

      That's totally impossible. Even the names are different.

      → Reply
  • »
    »
    5 years ago, # ^ |
      Vote: I like it +3 Vote: I do not like it

    Maybe you can find it here.

    → Reply
»
5 years ago, # |
  Vote: I like it +20 Vote: I do not like it

Good chance to become master :3

→ Reply
»
5 years ago, # |
  Vote: I like it +43 Vote: I do not like it

While my friends hang out with their girlfriends on Chinese Valentine's Day, I have to stay at home to participate in this round. Maybe I should see Computer Science as my girlfriend... Anyway, good luck and happy Chinese Valentine's Day~ :D

→ Reply
  • »
    »
    5 years ago, # ^ |
      Vote: I like it +17 Vote: I do not like it

    Now it became a sad Valentine's Day. It seems that Educational Codeforces round broke up with me. (T_T)

    → Reply
»
5 years ago, # |
  Vote: I like it -10 Vote: I do not like it

Hope it will not be unrated...

→ Reply
»
5 years ago, # |
  Vote: I like it +14 Vote: I do not like it

I want to become Expert again....!

→ Reply
  • »
    »
    5 years ago, # ^ |
    ← Rev. 2   Vote: I like it +17 Vote: I do not like it

    → Reply
  • »
    »
    5 years ago, # ^ |
      Vote: I like it +19 Vote: I do not like it

    I don't want to become Expert again, but it must will happen because I ranked 3500+th. QWQ

    → Reply
    • »
      »
      »
      5 years ago, # ^ |
        Vote: I like it +8 Vote: I do not like it

      Don't be discouraged. Come on next time.

      → Reply
    • »
      »
      »
      5 years ago, # ^ |
        Vote: I like it +12 Vote: I do not like it

      Don't worry about it,you can become candidate master again.I wish you will do it in a short time(maybe the next contest).

      → Reply
»
5 years ago, # |
  Vote: I like it +21 Vote: I do not like it

Wow, I see Benq registered today ... the day between IOI competition day1 and day2.

→ Reply
  • »
    »
    5 years ago, # ^ |
      Vote: I like it -10 Vote: I do not like it

    A good competitive programmer should be able to deal with that kind of workload.

    → Reply
»
5 years ago, # |
← Rev. 2   Vote: I like it +9 Vote: I do not like it

I am so worried because it is my first time to join a Codeforces Round.
Good Luck Everyone!
qaq

→ Reply
  • »
    »
    5 years ago, # ^ |
    ← Rev. 2   Vote: I like it +5 Vote: I do not like it

    good luck and have fun!

    → Reply
  • »
    »
    5 years ago, # ^ |
      Vote: I like it +38 Vote: I do not like it

    Its the worst thing you could do this evening...

    → Reply
  • »
    »
    5 years ago, # ^ |
      Vote: I like it +7 Vote: I do not like it

    OMG I feel SOOOOO SAD for you!

    → Reply
»
5 years ago, # |
  Vote: I like it -9 Vote: I do not like it

Let's bang this round.

→ Reply
»
5 years ago, # |
  Vote: I like it 0 Vote: I do not like it

What are the links to the light versions of Codeforces? Anyone?__

→ Reply
»
5 years ago, # |
  Vote: I like it +24 Vote: I do not like it

Wtf, can you pls speak about some specific conditions of round? Like anti-understandable tasks, queryforces and another awesome things

→ Reply
»
5 years ago, # |
← Rev. 2   Vote: I like it +72 Vote: I do not like it

Not actually participating in the round, but I guess a grey or green coder (normally capable of doing div.2 A) would cry when they see this problem statement...

→ Reply
»
5 years ago, # |
← Rev. 2   Vote: I like it +38 Vote: I do not like it

I have seen easy and difficult problems that were fun or boring.
But this round has outdone them all.

→ Reply
»
5 years ago, # |
  Vote: I like it +8 Vote: I do not like it

And I hate strings!

→ Reply
»
5 years ago, # |
← Rev. 2   Vote: I like it +57 Vote: I do not like it

Imagine having tasks with nice solutions and statements.

→ Reply
»
5 years ago, # |
  Vote: I like it +249 Vote: I do not like it

→ Reply
»
5 years ago, # |
  Vote: I like it +9 Vote: I do not like it

Educational Round...????

Seriously...???

→ Reply
»
5 years ago, # |
  Vote: I like it +37 Vote: I do not like it

Well, this looks so much like an education round that I decided to go to bed.

→ Reply
  • »
    »
    5 years ago, # ^ |
      Vote: I like it 0 Vote: I do not like it

    Educational Round is too dangerous to me,my code usually can be hacked easily.I have been hacked for four times in a short time.So,I didn't join the contest.

    → Reply
»
5 years ago, # |
  Vote: I like it +8 Vote: I do not like it

u good bro?

→ Reply
»
5 years ago, # |
  Vote: I like it +155 Vote: I do not like it

2 mins before the contest : watching youtube

2 mins after : reading problem A

15 mins after : still reading A

16 mins after : back to youtube :)

→ Reply
»
5 years ago, # |
  Vote: I like it +21 Vote: I do not like it

I guess Codeforces seriously wants to educate us by giving DIV 1 problems in DIV 2..

→ Reply
»
5 years ago, # |
  Vote: I like it +8 Vote: I do not like it

this problem A really knocked me out

→ Reply
»
5 years ago, # |
  Vote: I like it +58 Vote: I do not like it

this contest is a bad marketing strategy for harbour space

→ Reply
»
5 years ago, # |
  Vote: I like it +113 Vote: I do not like it

→ Reply
»
5 years ago, # |
  Vote: I like it +41 Vote: I do not like it

Stringforces

→ Reply
»
5 years ago, # |
← Rev. 2   Vote: I like it +82 Vote: I do not like it

→ Reply
»
5 years ago, # |
  Vote: I like it +23 Vote: I do not like it

the math person from discord is in the announcement pic, no wonder this round is bad.

→ Reply
  • »
    »
    5 years ago, # ^ |
      Vote: I like it +4 Vote: I do not like it

    Who is he just to be safe in future rounds ?

    → Reply
»
5 years ago, # |
  Vote: I like it +1 Vote: I do not like it

Seems like Div 1 :(((((

→ Reply
»
5 years ago, # |
  Vote: I like it +18 Vote: I do not like it

Stringforces??

→ Reply
»
5 years ago, # |
  Vote: I like it +2 Vote: I do not like it

The setter did a typo while writing division, he actually meant div1

→ Reply
»
5 years ago, # |
  Vote: I like it +3 Vote: I do not like it

I give up.

Not enough string power

I guess, I can't solve any of it before the Editorial :(

→ Reply
»
5 years ago, # |
  Vote: I like it +23 Vote: I do not like it

How on earth is this round educating??

→ Reply
  • »
    »
    5 years ago, # ^ |
    ← Rev. 2   Vote: I like it +1 Vote: I do not like it

    In problem A there is quote from Wikipedia, there might be some people don't know about! and now they learned it. is that not educational? xD

    → Reply
    • »
      »
      »
      5 years ago, # ^ |
        Vote: I like it 0 Vote: I do not like it

      I doubt they learned stuff specific to the problem. Quoting from the quote : then the string whose first letter comes earlier in the alphabet comes before the other string. 1's and 0's are not even alphabets!

      → Reply
»
5 years ago, # |
  Vote: I like it -8 Vote: I do not like it

Stringy round = hard round (?)

→ Reply
»
5 years ago, # |
  Vote: I like it -38 Vote: I do not like it

Makes me wonder, if a true Mathforces round could be held unrated in a seperate series, and this one, basically a stringforces, cannot; then what's the issues?

→ Reply
»
5 years ago, # |
  Vote: I like it +1 Vote: I do not like it

In this round the question has made in the upside-down universe that's why it seems hard in this universe

→ Reply
»
5 years ago, # |
← Rev. 2   Vote: I like it 0 Vote: I do not like it

Is it serious for us div2?

I think I have crippling depression.

→ Reply
»
5 years ago, # |
  Vote: I like it -6 Vote: I do not like it

It's more like div1 difficulty, RIP Rating :(

→ Reply
»
5 years ago, # |
  Vote: I like it -18 Vote: I do not like it

When a sensible contest with legitimate problems will be made

→ Reply
»
5 years ago, # |
  Vote: I like it -16 Vote: I do not like it

Negative, LOL.

→ Reply
»
5 years ago, # |
← Rev. 2   Vote: I like it +16 Vote: I do not like it

→ Reply
»
5 years ago, # |
  Vote: I like it +29 Vote: I do not like it

It was really a UNIQUE Educational Round.

I hope it will never ever repeat

→ Reply
»
5 years ago, # |
  Vote: I like it +6 Vote: I do not like it

This contest is so hard for Div2

→ Reply
  • »
    »
    5 years ago, # ^ |
      Vote: I like it +13 Vote: I do not like it

    But if this round is too eazy , how can we say it 'educational'?

    I think we can get more knowledge in a little more difficult round , right?

    → Reply
»
5 years ago, # |
  Vote: I like it -20 Vote: I do not like it

This round was majorly implementation based. Even the I/O was to be taken care of.

→ Reply
»
5 years ago, # |
  Vote: I like it -10 Vote: I do not like it

The most difficult EDU round

→ Reply
»
5 years ago, # |
  Vote: I like it -8 Vote: I do not like it

This educational round was terrifying to me :<

→ Reply
»
5 years ago, # |
← Rev. 2   Vote: I like it 0 Vote: I do not like it

why first three problems were so much harder than what we used to see in previous div2 rounds.

→ Reply
  • »
    »
    5 years ago, # ^ |
      Vote: I like it -9 Vote: I do not like it

    They weren't really much harder, but A has shitty statement and B, C has shitty implementation

    → Reply
»
5 years ago, # |
  Vote: I like it 0 Vote: I do not like it

When will the test public

→ Reply
»
5 years ago, # |
  Vote: I like it 0 Vote: I do not like it

Worst Educational Round to me.

→ Reply
»
5 years ago, # |
  Vote: I like it -10 Vote: I do not like it

This contest sucks. A and D are a bit interesting, but B and C are just like shit, especially B. Implementing is much harder than thinking. E is so standard that who knows AC automaton would easily solve it.

Well I know E is good for educational rounds, but I really disgust such problems like B and C appear in Edu rounds.

→ Reply
»
5 years ago, # |
  Vote: I like it +1 Vote: I do not like it

I could have slept an extra 2 hours instead of getting owned by this round :(

→ Reply
»
5 years ago, # |
  Vote: I like it +5 Vote: I do not like it

I hate problem C just because its code will be so long,and I cannot finish it.Isn't it write one thing for 4 times?

→ Reply
»
5 years ago, # |
  Vote: I like it +6 Vote: I do not like it

Sorry to say, this is the worst contest I have ever participated so far!

→ Reply
»
5 years ago, # |
  Vote: I like it 0 Vote: I do not like it

i think (and i wish :D) it will become THE most "not liked" contest announcement of all time.

→ Reply
»
5 years ago, # |
  Vote: I like it +22 Vote: I do not like it

Round started...

Thinking on A...

20 minutes later

Okey, I cannot write any solution, that I can prove. Let's write some shit.

Samples passed

Submit

OK

→ Reply
»
5 years ago, # |
  Vote: I like it 0 Vote: I do not like it

In problem E, what is the intended solution's time complexity?

→ Reply
  • »
    »
    5 years ago, # ^ |
      Vote: I like it 0 Vote: I do not like it

    Linear.

    → Reply
    • »
      »
      »
      5 years ago, # ^ |
        Vote: I like it 0 Vote: I do not like it

      could you explain your approach...

      → Reply
      • »
        »
        »
        »
        5 years ago, # ^ |
          Vote: I like it 0 Vote: I do not like it

        $$$a[i]$$$ denotes the number of strings that can be matched ending at $$$t[i]$$$, $$$b[i]$$$ denotes the number of strings that can be matched beginning at $$$t[i]$$$. So the answer is $$$\sum a[i]b[i+1]$$$.

        How to calculate those two things quickly? Can be done by two Aho-Corasick Automatons. One contains all $$$s$$$, the other contains all reverse strings of $$$s$$$.

        → Reply
  • »
    »
    5 years ago, # ^ |
      Vote: I like it 0 Vote: I do not like it

    Author's solution is $$$O(n \sqrt{n})$$$. You can write whatever you can.

    → Reply
»
5 years ago, # |
  Vote: I like it +3 Vote: I do not like it

this contest was implementation heavy , could not finish C. Please problem setters, consider duration of contest proportional to difficulty!

→ Reply
»
5 years ago, # |
  Vote: I like it +4 Vote: I do not like it

So the problems in edu rounds are not sorted by difficulties?

I think problem B & C are too difficult for div2 b c....

→ Reply
»
5 years ago, # |
  Vote: I like it 0 Vote: I do not like it

Why AC-Automaton got TLE on test 5?

58456132

→ Reply
  • »
    »
    5 years ago, # ^ |
      Vote: I like it +35 Vote: I do not like it

    You used a violent jump fail pointer in the quary function.

    → Reply
»
5 years ago, # |
  Vote: I like it +5 Vote: I do not like it

I should quit before submit anything.

But the better thing is I can join Div.3 now LOL

→ Reply
»
5 years ago, # |
  Vote: I like it +10 Vote: I do not like it

Horrible EDU ever

→ Reply
»
5 years ago, # |
  Vote: I like it +143 Vote: I do not like it

seriously, what is this B?

also A is hard to read :(

→ Reply
  • »
    »
    5 years ago, # ^ |
      Vote: I like it +14 Vote: I do not like it

    B is just a simple implementation problem. Sometimes you just have to spend some time reading the problem's statement and then spend some time coding some basic stuff. А is also about reading the statement. Why the fuck do you consider smth like "Pls output YES if n is odd and NO otherwise" as a nice problem for A?

    But low-skill kids prefer to write shitty comments instead of upsolving because it's so much easier, right?

    → Reply
    • »
      »
      »
      5 years ago, # ^ |
        Vote: I like it +10 Vote: I do not like it

      what you mean "low-skill kids"? why are you that aggressive?

      this picture is just joking about my feeling on B : /

      and in round I skip B and solve CD, cuz B is too hard to read(for me)

      in fact, to me, I'm just can't read out what A,B want to explain.

      and I solved that B after round in 5min.

      A&B 's coding time is shorter than 15min for me, but too hard to read

      I spent near 1hour in total on reading A,B and understand them : /

      well, ok, it's just my english noob , ok : /

      and personally, I think this round's problem it self is not bad...

      but the statement is really hard (at least for me : (

      I think a good problem should take more time on thinking but not reading :p

      → Reply
      • »
        »
        »
        »
        5 years ago, # ^ |
        ← Rev. 2   Vote: I like it +3 Vote: I do not like it

        Actually, your meme is a nice one, I liked it, should’ve point that out directly. I just upset by the fact that people downvote nice contest. It’s kinda sad, you know. Pls register some fake accounts and upvote the blogpost back.

        → Reply
    • »
      »
      »
      5 years ago, # ^ |
      ← Rev. 2   Vote: I like it 0 Vote: I do not like it

      and also

      Why the f*** do you consider smth like "Pls output YES if n is odd and NO otherwise" as a nice problem for A?

      I didn't remember that I said things like that :p

      → Reply
»
5 years ago, # |
  Vote: I like it +11 Vote: I do not like it

The Education Round requires a lot of thought.
It doesn't seem to want to be passed on as a simple idea.
But ranker's code is simple!

→ Reply
»
5 years ago, # |
  Vote: I like it +9 Vote: I do not like it

Educational StringForces Round 70 (Div.1)

→ Reply
»
5 years ago, # |
← Rev. 2   Vote: I like it -48 Vote: I do not like it

The Problem D is just a easy problem, why did u put it on D?

The Probelm E is also a easy ACAM problem, why did u put it on E?

The Problem A is not a div2-A...

I use my another account MtOI to join this contest (just for rating),

at first I wish to become Master, but the result is terrible.

I feel very disappointed for this contest...this contest does not fit many people.

→ Reply
»
5 years ago, # |
  Vote: I like it +243 Vote: I do not like it

Hey. I want to share my thoughts about this round and your reaction to it.

I agree with the opinion that the first problem has an unpleasant wording for beginners. If I were a round writer, I would try to do something with it or replace the problem. However, I do not see anything particularly terrible in this problem. Moreover, it is in an educational round that one can more likely expect a problem that will teach you to read a formal mathematical statement. The implementation of the solution is really simple, I think that many participants were too lazy to delve into its statement.

The second problem is very well formulated, has a short and understandable solution. It can be interpreted as dynamic programming or even as some natural idea (brute force). Perhaps this problem is difficult for position B, but it is far from div1 level, many div2 participants have solved it. It doesn’t require any specific knowledge.

I did not delve into the following problems, but it seems they are fairly distributed in complexity, using different ideas (I noticed not only strings, but also constructive and data structures).

I note that all the problems were soundly formulated and worked out by the authors: they contain examples along a statement, notes for examples from the statement. The number of questions about statements in this round was very small and there was no need for corrections in the statements. There were no troubles with the correctness of tests or writer's solutions. I believe that the writers have missed a bit with the complexity of the first problems and their attractiveness for beginners, but nothing more.

The team of writers of the educational rounds really delights me with their productivity, stable quality and performance. I am very grateful to the guys for their work and contribution to the development of the community. They have prepared a huge number of interesting problems and continue to do so. The vast majority of educational rounds are very good. This round was not ideal, but preparing rounds is creativity, this happens.

I strongly disagree with those who wrote sharply and disrespectfully about this round. I would like the website community to be more able to appreciate the efforts of those who work on a content and forgive mistakes.

→ Reply
  • »
    »
    5 years ago, # ^ |
      Vote: I like it +13 Vote: I do not like it

    In my opinion, all the problem (I mean, at least A-E, which I came up with the solution) was easy to understand. Also, if you choose good way, implementation can be simple enough and easy to debug. I don't have agreement or disagreement about the difficulty or the problem order (I think it's far more harder than writing a problem and the ability to estimate the problem is very special skill). But at least, I think there are nothing to complain about the quality of each problem. I hope that writers won't be disappointed and hold such a contest again!!

    → Reply
  • »
    »
    5 years ago, # ^ |
      Vote: I like it 0 Vote: I do not like it

    In my opinion, these problems are valuable for someone new to Codeforces contests, in which you need to think a lot. These problems can improve one's implementation skills and thinking skills greatly. However, contestants usually estimate a contest with the time they need to come up with the solution and solve each problem, especially problem A and B. These problems worth doing, but they are somehow unpleasant for a Codeforces contest, for problem A needs time to think, and problem B needs time to write.

    → Reply
»
5 years ago, # |
  Vote: I like it -8 Vote: I do not like it

it was the best contest till now. loved it to solve one question.

→ Reply
»
5 years ago, # |
  Vote: I like it +13 Vote: I do not like it

People are getting triggered just because A was slightly harder than usual :thonk:

→ Reply
»
5 years ago, # |
  Vote: I like it +21 Vote: I do not like it

Congratulations for the revival!

→ Reply
»
5 years ago, # |
  Vote: I like it +14 Vote: I do not like it

Is it rated?

→ Reply
»
5 years ago, # |
← Rev. 2   Vote: I like it +6 Vote: I do not like it

It feels like my girlfriend left me during the maintainess of Codeforces, though i don't even have one.

→ Reply
»
5 years ago, # |
  Vote: I like it +28 Vote: I do not like it

So what was wrong with Codeforces?

→ Reply
»
5 years ago, # |
← Rev. 2   Vote: I like it -8 Vote: I do not like it

So, when will we have system testing? Or is it done before?

UPD: I've just seen the announcement. The Open Hack Phase have been intended.

→ Reply
»
5 years ago, # |
  Vote: I like it +5 Vote: I do not like it

Is the hacking phase over?? Or will it be extended?

→ Reply
»
5 years ago, # |
  Vote: I like it +57 Vote: I do not like it

Looks like someone is not happy with this round. And he hacks...

The website

→ Reply
»
5 years ago, # |
  Vote: I like it +15 Vote: I do not like it

Wait for becoming master all day . And seems it needs another day for open hacking QAQ

→ Reply
»
5 years ago, # |
  Vote: I like it 0 Vote: I do not like it

Auto comment: topic has been updated by awoo (previous revision, new revision, compare).

→ Reply
»
5 years ago, # |
  Vote: I like it +25 Vote: I do not like it

Why is the editorial published when the open hacking phase is still running?

By the way, this is one of the particularly good round, where every successful attempt to solve a problem gives great sense of accomplishment.

→ Reply
  • »
    »
    5 years ago, # ^ |
      Vote: I like it +16 Vote: I do not like it

    What is wrong with editorial published while open hacking is running?

    → Reply
    • »
      »
      »
      5 years ago, # ^ |
        Vote: I like it +10 Vote: I do not like it

      To hack a problem, you need first to solve it correctly. with the editorial published, hacking becomes easier because everyone knows the correct solutions.

      → Reply
      • »
        »
        »
        »
        5 years ago, # ^ |
          Vote: I like it +8 Vote: I do not like it

        Isn't that a good thing?

        → Reply
        • »
          »
          »
          »
          »
          5 years ago, # ^ |
            Vote: I like it 0 Vote: I do not like it

          Well, that's relative. For me, at least, I like the part of solving the problem correctly first to be able to hack other solutions.

          → Reply
»
5 years ago, # |
  Vote: I like it 0 Vote: I do not like it

:( I very hoped I can become blue. :( but so sad with Education 70.

→ Reply
»
5 years ago, # |
  Vote: I like it 0 Vote: I do not like it

Got TLE on problem E during the contest because I used a map to count number of occurrences of numbers in range [0,2*10^5]. I hate myself :(

→ Reply
»
5 years ago, # |
  Vote: I like it -19 Vote: I do not like it 
UPD: Our friends at Harbour.Space also have a message for you:
Hello Codeforces!
Ready to get deep?

What do you mean? My rating? It will go deep for sure

→ Reply
»
5 years ago, # |
← Rev. 2   Vote: I like it 0 Vote: I do not like it

This round had a good distribution between problems (by numbers of contestants solved each one). Sadly, I performed so badly, feel a bit sad {'-'}. Also its a lovely curve or maybe Im wrong?

→ Reply
»
5 years ago, # |
  Vote: I like it -7 Vote: I do not like it

How I thought of this round:

Problem B was a high quality problem. Problem B for a Div 2 B is not so high quality.

→ Reply
»
5 years ago, # |
  Vote: I like it +110 Vote: I do not like it

→ Reply
»
5 years ago, # |
  Vote: I like it 0 Vote: I do not like it

https://mirror.codeforces.com/contest/1202/submission/58463646 https://mirror.codeforces.com/contest/1202/submission/58463769 why one of the two solutions give tle??

→ Reply
»
5 years ago, # |
  Vote: I like it +46 Vote: I do not like it

→ Reply
»
5 years ago, # |
  Vote: I like it +87 Vote: I do not like it

You know what? I don't care contribution now. I just wanna say the contest is terrible.

Did you ever seen ANY Div.2 A like this one? Multiple queries, length up to $$$10^5$$$, are you serious? It's Div.2 A, not Div.2 C or even harder!

The same problems on B and C, I'm not saying they are bad problems, but they are just too complex for being the first three problem in Div.2.

For problem D and E, their idea are similar to other problems. I swear I saw the exactly idea of D(add $$$\binom{k}{2}$$$ to get any number) in other problems. And problem E's first key idea is the same as CNOI 2016 D1T1 "Excellent Partition". So I think these two problems are not good-quality enough.

No Codeforces contest is flawless, but this one is so awfully flawed!

→ Reply
  • »
    »
    5 years ago, # ^ |
      Vote: I like it +6 Vote: I do not like it

    Yes, looking at feedback, it's clear now that we (personally, myself) overestimated our participants. It seems like we need just one more task before A.

    But for me, personally, there are no problems with current D and E. Problem D was not hard and, I believe, you can invent the solution without knowing it beforehand. And problem E appeared 3 years ago — I think, it's not critical.

    → Reply
    • »
      »
      »
      5 years ago, # ^ |
        Vote: I like it 0 Vote: I do not like it

      I agree that originality shouldn't be a concern for educational round. On the other hand I feel that the right order for BCD should be D — B — C.

      → Reply
  • »
    »
    5 years ago, # ^ |
      Vote: I like it +16 Vote: I do not like it

    The topic is not too difficult. There is not much problem with the number of questions.

    → Reply
  • »
    »
    5 years ago, # ^ |
    ← Rev. 2   Vote: I like it +61 Vote: I do not like it

    I don't agree on your opinion, I didn't paricipate in this contest, but i have to say, this contest is not bad at all!

    You say the problem is too hard, so you don't like them. But in fact, there are still up to 3000 people solved it.

    What kind of Div.2 A do you like? A 500 points problem? Or a even 100 points problem? Codeforces is not a place for you to practice the basic C++/python/Java skills.

    And the difficulty distribution is also good in this contest. Number of accepted people on each problem: 3441-1359-375-865-71-6, every two problems can differentiate two colors. Do you like a contest with number of accepted participants:10000-10000-10000-100-1?

    I understand your disappointed feeling when you opened the A, B and find yourself can't solve any of them, but it's not a fair reason for you to complain that this is not a good contest.

    If this contest is just lacking in a 500/600-points problem, it's still a good contest.

    In the end, i still want to add one point, the writer spent thousands of time on this contest, what would he think if he see you complaining the contest just because of the problem is too hard for you? Have you ever prepared a contest? I really don't understand why there's so much downvotes of the blog and so many complaination of the problem.

    I always agree that Codeforces is the best CP platform all over the world, but i'm very worried about this people who downvote the blog or send their complanation just because the problem is too hard for them.

    → Reply
    • »
      »
      »
      5 years ago, # ^ |
        Vote: I like it +20 Vote: I do not like it

      I didn't say the problems are too hard. I'm saying the problems don't match with their ID. If this is a Div.1 Round instead, I may say those problems are slightly easier.

      I've never seen a Div.2 A or B like this. As you can see, problem B here has a difficulty of 1700, which is close to regular Div.2 D. And problem C's difficulty is shockingly even higher: 2100, it means in general, those who solved Div.2 C is able to get to level Master, isn't that ridiculous?

      I wish the following contests can be more "regular", and their problems can be "close to normal-difficulty problems", but not like this one, one of the most annoying contest, Educational Codeforces Round 70.

      → Reply
      • »
        »
        »
        »
        5 years ago, # ^ |
          Vote: I like it +57 Vote: I do not like it

        I agree that this contest's problems' difficulty doesn't match their ID, but absolutely it's not a fair reason for the blog to get so many downvotes and so much complaination.

        You could just imagine this is contest without problem A. Getting the order of problem C and problem D wrong is a slight mistake. You could be polite and comment under the blog and say: "We want a easier A, and wish the difficuly of the problem match their order." istead of say:

        one of the most annoying contest, Educational Codeforces Round 70.

        And, this contest neither contains a "broken" problem nor leaks problem before it started. One shouldn't speak so impolitely to the author, I sincerely hope that those who said this contest "is the worst ever" can apologize to the writers of the round, for their hard work on the contest, for their hark work on the past all educational contests, for their hard work on making Codeforces better and better.

        → Reply
    • »
      »
      »
      5 years ago, # ^ |
        Vote: I like it -10 Vote: I do not like it

      Have you ever prepared a contest?

      Check it yourself, and also Comet OJ — Contest #9 & X Round 3.

      Codeforces Round #564 is mainly prepared by me, I poured time and energy into it. After that, I learned how hard it is to prepare a high-quality round, and also, how important it is to prepare a high-quality round.

      Because you "spent thousands of time", you should make it high-quality to be responsible for yourself.

      Because here is Codeforces, "the best CP platform", you have to make it high-quality to be responsible for thousands of participants.

      One reason for CF to be "the best CP platform" is that it guarantees the difficulty of problems, and we can know a problem's difficulty by its position. Problem writers should follow the standard of difficulties.

      Again, efforts can't win respect without taking responsibility.

      In addition, good problems can form a bad contest.

      Also, a list of logical mistakes:

      • But in fact, there are still up to 3000 people solved it

      Usually, there are more. And you should also consider the time people used to solve it.

      • Or a even 100 points problem?

      We want problems in normal difficulty, not too difficult nor too easy.

      • Do you like a contest with number of accepted participants:10000-10000-10000-100-1?

      I can't see any reason for PinkRabbit to like this distribution.

      • when you opened the A, B and find yourself can't solve any of them

      I think he could solve it, but found it was harder than usual.

      • the problem is too hard for you

      I think you meant "you can't solve them", and that's not true. We say "it's too hard" to mean it's harder than usual.

      • Have you ever prepared a contest?

      Discussed above.

      → Reply
»
5 years ago, # |
  Vote: I like it +16 Vote: I do not like it

When will the system testing start?? Will it take one more day :XD

→ Reply
»
5 years ago, # |
  Vote: I like it +16 Vote: I do not like it

The objective of Educational rounds should be to educate. One can't learn much from conventional Div2 A and B difficulties, and to think of it, real learning begins with discomfort which one slowly conquers. I think the contest was just fine for serving this purpose, since the techniques it covered are standard-ish while being slightly disguised by more involved problem statements. One may argue against the high amount implementation of B and C, but hey, learning to implement long solutions with brevity is also an invaluable skill. For example, I realised after the contest that I could simply have used a (multi)set to query suffix maximum and minimum on the fly instead of dealing with four separate cases in suffix maxima/minima of x/y. I could only have realised this mistake in an implementation-heavy contest.

In short, Educational rounds are perfectly fine as long as they introduce relatively standard techniques.

→ Reply
»
5 years ago, # |
  Vote: I like it +25 Vote: I do not like it

I think we say the round is bad doesn't mean we disrespect authors.I like these problems.I just think they should be replaced in better positions.(A->div.2B,B->div.2C,C->div.2D,D->div.2C,E->div.2D).

→ Reply
»
5 years ago, # |
  Vote: I like it 0 Vote: I do not like it

I think C can also be done by efficiently brute forcing with the help of Range min/max lazy propagation segment tree. That would be overlkill though. Correct if I am wrong.

→ Reply
  • »
    »
    5 years ago, # ^ |
      Vote: I like it 0 Vote: I do not like it

    There is no need for lazy propagation, you can precompute prefix sums and use those values for the min/max segment trees.

    I used ST since I didn't want to think the linear solution xD

    58444732

    → Reply
»
5 years ago, # |
← Rev. 5   Vote: I like it +21 Vote: I do not like it

maybe it's wrong to send that comment out.

I'm so annoyed at beginning and send the to comments.

but infact I don't want to argue like that at beginning. sorry.

maybe it's I have not sleep for 36 hours so my brain dead...

I'm idiot... made a lot of spam at here... sorry...

→ Reply
  • »
    »
    5 years ago, # ^ |
      Vote: I like it +22 Vote: I do not like it

    First of all, I'm very sorry about what I did. You see, I'm just a pupil. I learnt to use Codeforces just one year ago. I don't even know I will appear in PikMike's blog! I become happy only because "Successful Hacking Attempt". I do this just for fun and I hope you can forgive me. Ignore me. zdw1999 is the best hacker. Thank you. I'm really sorry.

    → Reply
  • »
    »
    5 years ago, # ^ |
    ← Rev. 2   Vote: I like it 0 Vote: I do not like it

    I am so sorry for being normal with you

    → Reply
»
5 years ago, # |
  Vote: I like it +17 Vote: I do not like it

I've learnt many things from this round, it improves my strings manipulation. Thank authors

→ Reply
»
5 years ago, # |
  Vote: I like it +8 Vote: I do not like it

is the list of best hackers correct? for example, it's showed that awasd has only 3 successful hacks, although i can see he made 5 successful hacks.

→ Reply
  • »
    »
    5 years ago, # ^ |
      Vote: I like it +1 Vote: I do not like it

    It's really weird but two of the hacks made don't appear as hacks but as Wrong Answers on test 11. Anyways, if only the 3 hacks count shouldn't I be on the 5th position? :P (I made 4 hacks Lol)

    → Reply
  • »
    »
    5 years ago, # ^ |
      Vote: I like it +10 Vote: I do not like it

    Hmm, I retrieve that list from CF api. Looks weird.

    I guess I can just hide the table for this contest, maybe I'll fix it before the next one.

    → Reply
»
5 years ago, # |
  Vote: I like it 0 Vote: I do not like it

It's too hard!!!!!!!!!!!!!!!!

→ Reply
»
5 years ago, # |
  Vote: I like it 0 Vote: I do not like it

I am former candidate master and I can't solve A. Would tourist solve A?

→ Reply