duality's blog

Codeforces Round #884 (Div. 1 + Div. 2)
By duality, history, 5 months ago, In English

Hello, Codeforces!

I invite everyone to participate in Codeforces Round 884 (Div. 1 + Div. 2), which will start on 11.07.2023 17:35 (Московское время). The round is a combined round and will be rated for everyone.

You will be given 8 problems and 3 hours to solve them. One of the problems is divided into two subtasks. The scoring distribution will be:

$$$500$$$ — $$$1000$$$ — $$$1250$$$ — $$$1500$$$ — $$$2000$$$ — $$$(2000+1000)$$$ — $$$3500$$$ — $$$4000$$$

All problems are written and prepared by me. I would like to thank:

I look forward to your participation and hope you enjoy the problems. Good luck!

UPD 1: Editorial

UPD 2: Congratulations to the winners!

  1. cnnfls_csy
  2. tourist
  3. -0.5
  4. ksun48
  5. gyh20
  6. heno239
  7. jiangly
  8. ecnerwala
  9. neal
  10. Heltion

and congratulations to cnnfls_csy and orz for solving problem H!

  • Vote: I like it
  • +1077
  • Vote: I do not like it

»
5 months ago, # |
  Vote: I like it +29 Vote: I do not like it

Now the testers can comment

→ Reply
»
5 months ago, # |
  Vote: I like it +61 Vote: I do not like it

As a tester, I comment

→ Reply
  • »
    »
    5 months ago, # ^ |
      Vote: I like it +44 Vote: I do not like it

    As a participant, I replied

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

      I Guess that you have not been participated in the contest for last year.(except the one in June)

      → Reply
»
5 months ago, # |
  Vote: I like it +98 Vote: I do not like it

It's amazing that a single writer prepared all the problems for a Div. 1 + Div. 2 contest! Hope the problems are interesting :)

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

Looking forward! Score distribution means I might finally get a D solve again ;)

→ Reply
»
5 months ago, # |
  Vote: I like it +50 Vote: I do not like it

Is the cat in Golovanov399's profile coughing?

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

I also participate and try to increase my rating

→ Reply
»
5 months ago, # |
  Vote: I like it +40 Vote: I do not like it

As a tester, I can confirm the hardest problem is harder than the easiest one.

Good luck!

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

    As a tester ( giving that he participates ), I can confirm tourist will solve at least one problem.

    Good luck!

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

hope to become green in this contest.

→ Reply
»
5 months ago, # |
  Vote: I like it -12 Vote: I do not like it

Why is problem number 6 score (2000+1000)? Is it because of subtasks? Asking because I have never seen subtasks on CF :)

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

    There will be F1 (score 2000) and harder version of the same problem as F2 (score 1000).

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

    It will probably be the easy version with 2000 points and the hard version with 1000 points. For example, they were split equally in the following competition, but not equal points this time: https://codeforces.com/blog/entry/116091

    → Reply
»
5 months ago, # |
← Rev. 3   Vote: I like it -11 Vote: I do not like it

One good contest for me and I will be surely on my peak.

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

As a tester, video editorials for most problems will be on my channel after the contest

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

Hoping to reach blue

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

i will try to become pupil on this contest

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

I was just wondering, is there a reason why this round is combined Div.1 + Div.2, while the rounds are usually separate Div.1 and Div.2? I understand that rounds with prizes are combined to let everyone have a chance for a prize but this round is not one of those.

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

Here we go, Go to Grey again :)...

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

can anyone tell me how can I become a tester?

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

are you from the same London as Justin Bieber?

→ Reply
»
5 months ago, # |
  Vote: I like it -93 Vote: I do not like it

I thinks that frequency Of DIV : 4 contest is reduced so much??? As earlier DIV : 4 almost happen every month But of now there is no DIV : 4 contests happening.... It's very long time that No DIV : 4 contest has been happened....If it is like this what will happen to the participants like us which are "newbie" on codeforces... Isn't It?? What's Your opinions On this... Just personal Feeling's.. If anyone get's offended by this Sorry for that(:

→ Reply
  • »
    »
    5 months ago, # ^ |
      Vote: I like it +51 Vote: I do not like it

    I mean you could actually try solving some harder problems?

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

Is +66 delta too much to ask for!!!

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

    and shameless me asking for 113+ delta xD

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

    I think you need about top 700 overall to get this delta

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

As a partcipant, I excited

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

Enjoy the three hours and get rating

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

Question:

Sir, I am a newbie. So am I eligible for this contest ?

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

    yes, anyone is eligible for this contest regardless of ratings.

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

      Thanks @amit_pandit_15 for replying. So if I was able to solve only single problem in this hard will this decrease my rating badly. What do you think?

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

        In starting contests(for like first 3-4 contests) the ratings increases only, even if don't have good performance, since you have given only 2 contests, solving even one question will increase your ratings.

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

        I think getting at least 2 problems right should be enough for you to get a +ve delta

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

Hope to get close to CM :)

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

    i hope to become a specialist again. Are u a third-year student?

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

      I gave my 6th semester exam before this summer vacation , i am currently in 7th semester now.

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

    poorpul

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

Tonight, I am ready for the first battle to achieve the prestigious Purple Rank.

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

I will try to solve A-D ASAP to have time to solve E, sound interesting!

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

I'm sad. I have a summer camp so I can't participate. I will definitely up-solve the problems in the contest tho. To everybody who is taking the contest, GL & HF!!!

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

I wish I can see a Lockout Between tourist and Benq :) ... What is ur opinion guys ?

→ Reply
»
5 months ago, # |
  Vote: I like it -33 Vote: I do not like it

is tourist going to surpass Benq in this contest? make your bets: like for yes dislike for no

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

I hope we don't go back to the green name

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

Does this mean that our ranking will be more than 1,000 lower than the usual Div.2, and it will be more difficult to add points, because the experts of Div.1 will also participate.

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

poorpul

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

i wanted to see tourist at 1 again.

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

wait i cannot register anymore, why? Edit: i tried to register 10 mins before contest

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

    now register in extra registration time

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

I'm unable to submit It is giving me error you should be registered to be able to submit

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

Is so hard for me

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

Damn I had AC on the first problem, but I tried other solutions, so I resubmitted 2 times and lost 100 points :'(

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

Slowly proceeding towards my fav colour :)

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

    I wouldn't say that's slowly, that's a big step.

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

      Ah yes, I am really missing Cyan, so I decided to take a big step :)

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

        just kiddin, if you didnt submit all of them at once you would have lost just a little rating. you are closer to CM no worries

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

is cf-predictor working? it's not working for me

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

i am going to get demoted for sure.

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

DsolvingForces

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

Balanced as everything should be ):

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

speedforces

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

Wow,5500 submissions on problem D,codeforces has become leetcode. Cheaters everywhere.

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

Rating is not increasing ,neither the contributions, what should I do now ?

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

Problem A

May I know why this condition is not valid

if(a == 1){
    cout << 2 << '\n';
} else {
    cout << 1 << '\n';
}
→ Reply
  • »
    »
    5 months ago, # ^ |
      Vote: I like it 0 Vote: I do not like it

    1 2

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

    b can be two while a = 1

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

    Consider the case where a is 1 and b is 2.

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

    test case :

    a=1,b=2

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

    If $$$a = 1$$$ and $$$b = 2$$$ you get wrong answer. Then the first player can take $$$2$$$ and remaining stones are $$$0$$$ total so second player loses.

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

    a = 1 and b = 2 in this case you print 2, but then the first player can win in one move.

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

    Given a=1, b=2; you chose 2 stones. first player removes b (2) stones, leaving 0 stones, second player loses.

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

    What if B is 2, then first person will reduce 2 from 2 (your answer) and second person cannot move.

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

    got it, thank you

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

    what if b=2

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

ConstructiveForces

→ Reply
»
5 months ago, # |
  Vote: I like it +209 Vote: I do not like it

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

    they should be flipped

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

    Bro , your jump from expert to candidate master is the highest jump ever recorded in human history,may I know the hardwork behind this success

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

How to solve C?

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

    It's not possible to sum odd and even index numbers. Try it.

    So you have to get max sum from either odd or even index numbers.

    The odd (in this case) can be summed up (or deleted) and the even have to be deleted. And vice versa.

    Also check for the case when all numbers are negative.

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

so what was the edge case for C?

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

    are you checking maximum subarray sum for odd and even indexes??

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

      yes

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

        It should be a maximum subsequence. For the array 1 -1 -1 -1 1 you can repeat move on 3rd and 2nd then you will get 2

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

          Ohh got it, thanks.

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

          1 -1 -1 -1 1 test case broke my solution. Did not realize that you can safely discard negative elements.

          → Reply
»
5 months ago, # |
  Vote: I like it +61 Vote: I do not like it

Codeforces Round #884 (Div. 1 + Div. 2)
ConstructiveForces

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

    Algorithm (X) Construction (O) Contest.

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

Speedforces from A to D

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

    how to solve C?

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

      Simulate the operations for a few cases. You will observe that the final array collapses to a subset of one of the following index sets: {1,3,5,7,9...} or {0,2,4,6...}. Moreover, no adjacent elements can be part of the final sum together.

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

        what about the case -1 1000 -1 -1, shouldn't the answer be 1000?

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

          yes. In this case, the subset of {1,3,5,...} chosen by us is simply {1}.

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

    How to solve D?

    → Reply
    • »
      »
      »
      5 months ago, # ^ |
      ← Rev. 2   Vote: I like it 0 Vote: I do not like it
      • repeat any string with unique elements, length of first non-divisor
      • 26! = 4e26 --> N < 4e26 always has answer
      → Reply
      • »
        »
        »
        »
        5 months ago, # ^ |
          Vote: I like it +41 Vote: I do not like it

        Answer exists because $$$lcm(1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23,24,25,26)$$$ $$$>n$$$, not because $$$26!>n$$$.

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

    skill issue

    → Reply
»
5 months ago, # |
  Vote: I like it +49 Vote: I do not like it

teach me E

→ Reply
»
5 months ago, # |
  Vote: I like it +33 Vote: I do not like it

Why does every problem in this contest feel constructive? 🤡

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

Problem E is cool!

Though ABCD were absolute speedforces which I really failed, after solving E it didn't matter

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

How to solve C, I understand that I should always remove the current minimum element, but I had no idea how to efficiently implement that?

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

    you can only sum even index with even and odd index with odd so you need to calculate the maximum of both.

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

Swap(C,D), D was very straightforward unlike C.

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

wonderful problems!

→ Reply
»
5 months ago, # |
  Vote: I like it +55 Vote: I do not like it

so huge gap between D and E

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

Great contest! 2 problems with hello world solution is insane :D

→ Reply
»
5 months ago, # |
  Vote: I like it +125 Vote: I do not like it

GuessForces

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

    Please explain E.

    → Reply
    • »
      »
      »
      5 months ago, # ^ |
      ← Rev. 3   Vote: I like it +8 Vote: I do not like it

      I guessed the solution of E but don't know how to prove it.

      For (i, j) such that 1<=i<=n-1, 1<=j<=m-1, we must have (i, j)==(i+1, j+1) (we denote a[i][j]=0) or (i+1, j)==(i, j+1) (we denote a[i][j]=1), then for any valid grid, there must be some f[i] and g[j] such that a[i][j]=f[i] xor g[j]. Then we can solve the problem by dsu.

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

        I have been thinking for an hour but still cannot come up with a conclusion, can you give me a rough idea?

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

          think not about the letters, but about the grid of choice which diagonal contains the same elements in 2x2 squares — 1/0. All the lines of the grid are the first or the reversed first (suppose you know the first row and the first element of the second — you will see that the second is uniquely restored). Then check if it is possible — a system of disjoint sets and a top-down/left-to-right scanline

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

            apparently, the second part can be made much easier :)

            (Editorial is already out)

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

              Can I ask how you found this pattern? I couldn't construct objective examples for me to observe during the competition. Did you figure it out just by looking at the samples?

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

                in samples there is "square"

                1 ... 1

                .......

                1 ... 1 — YES

                1 ... 1

                .......

                0 ... 1 — No

                from that and looking at n = 3 m = 3 cases

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

shout out to ur mom and ur 1e9 copies for problem E

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

As a leetcode refuge, I really enjoy these problems, even if I solve a few each time. I can feel my brain working ;p. Each problem seems so easy after I finally solve it, but before that I might spend an hour on it.

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

Amazing contest! Had fun solving A to D, each problem had some beautiful insight hidden — which apparently, I was too dumb to notice, hence overkilled A with DP :X

Cheers to -100 delta, and 3 hours of absolute fun! Kudos to the author, and the entire team. Looking forward to future contests by duality!

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

    No way you used dp on problem A hahaha. Btw, it is always helpful to check the leaderboard. If a lot of people are getting AC on a given problem and you are stuck on it, chances are the solution is much easier than it seems.

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

Someone tell me how to solve "B. Permutations & Primes" problem?

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

    Anything that includes 1 and 2, but doesn't include 3 has prime MEX. So we place 1 and 2 in the middle and 3 all the way to the side, to maximize number of such segments.

    Now, anything that doesn't include 1 can't have prime MEX, so now we only need to consider segments that contain 3 and 1. The only way this can fail to have prime MEX is if it includes 2 but not 4. So, we place 4 right next to 3 to minimize such segments. Now. We only need to consider segments that contain 1 2 3 and 4. These have prime MEX unless they contain 5, so we place 5 all the way to the other side of 3 and 4.

    After this you can fill in the rest of the numbers arbitrarily.

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

In c is this approach right ?

If there are all negatives , print max of them . Remove all the consecutive negatives from front and back . Move from left to right , if you see a subarray of negative numbers and the size is odd . Add the two positives at two end and delete all negatives and those two. If the subarray negative numbers size is even , add the max of two positive at two ends and remove negatives and those two positives .

At the very end after traversing , check if sum of odd indices is greater than sum of even indices . Print max of them ?

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

I did not partecipate the contest but I Will try to upsolve. I think problem C can be done through DP. Is this the right way to go?

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

    Yes, DP is possible, but greedy is also possible

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

      Ok I Will try both approaches. The first thing which came to my mind when looking at it Is DP. Do you think the DP solution is hard to code?

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

    I think greedy is easier.

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

E destroyed my brain

→ Reply
»
5 months ago, # |
  Vote: I like it +114 Vote: I do not like it

What a gem of a round! E and G are just stunning problems, and the rest is very good also.

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

c>>>>>>d anyone?

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

    still more people solved C dont know why

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

    hmmm maybe? dunno, try multiple cases and you ll notice that you can get any subset of even or odd positions

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

coloringforces

anyway, it was a nice contest, really liked the problems :D

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

    what is the idea behind the d problem?

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

      The min distnict charcter in ansere is always first non-diviser of the given n ,,why this approach will work because let suppose x is not divide and then any multiple of x never divids n like 2x,3x,4x,5x... so on.and for ex. (3x+1) divides the n then the matrix of size 3 cross something and somthing cross 3 never be bad ..hope you understand the approach

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

        Thanks i was storing the total factors of n but got it now

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

    Why coloringforces? 0-1 coloring applies only to E I think

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

Wow! Superfast editorial with hints..

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

I think C > D......

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

want more frequency in contests

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

blazzing fast editorial

→ Reply
»
5 months ago, # |
← Rev. 2   Vote: I like it +21 Vote: I do not like it

Maybe testdata of F1 and F2 is too weak? My O(n^2) solution for F1 successfully passed F2. https://codeforces.com/contest/1844/submission/213394774

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

    and to my surprise, it even faster than most of O(nlogn) solutions.

    → Reply
    • »
      »
      »
      5 months ago, # ^ |
        Vote: I like it +33 Vote: I do not like it

      Hacked. A case containing lots of gaps that are less than $$$|c|$$$ but where twice the gap is more than $$$|c|$$$ causes your code to repeatedly erase from the front of the list, achieving $$$\mathcal{O}(n^2)$$$ behaviour.

      Unfortunately, I did not anticipate this approach before the round, so the tests did not contain this type of case.

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

        Also I saw this submission, may be it can be hacked too.

        → Reply
        • »
          »
          »
          »
          »
          5 months ago, # ^ |
            Vote: I like it +26 Vote: I do not like it

          Thank you for pointing out this submission. I hacked it too, using a test where only one small value satisfies the check_val condition.

          → Reply
»
5 months ago, # |
← Rev. 3   Vote: I like it +33 Vote: I do not like it

Good problems and strong pretest! I ranked 377 when the contest ends, and rank 377 after the system test. The only thing needs to mention is that difficulty gap between D and E is too large.

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

    Do you think you will get master?

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

      I don't know. Can anybody use the rating predictor to predict my rating changes for this contest? I am not able to use Chrome since it gives me 403/forbidden error.

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

        predictor gives me +70 for you

        congratulates for master bruh :)

        hope for me reaching cyan , i have been fighting for too long TOT

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

          how to use the CF predictor? I used to just use the site but I get a 502 error. How do you use the extensions?

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

    didn't you quit CP or something?

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

I hope to become an expert：）

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

I really enjoyed solving problems of this round, problem C is my favourite problem now, it is very interesting. But i have a problem, I have "hack it" button after the ending of the round

→ Reply
»
5 months ago, # |
  Vote: I like it +26 Vote: I do not like it

orz Orz

→ Reply
  • »
    »
    5 months ago, # ^ |
      Vote: I like it +34 Vote: I do not like it

    Thank you.

    People with rating predictors, could someone tell me my expected delta?

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

Honestly such a well organized contest, I thank everybody involved.

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

I am trying to figure out what is wrong with my solution https://codeforces.com/contest/1844/submission/213344967

It appears that the checker output does not show failed test case. Is it intentional? If so why is that?

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

    I think from one of the odd or even sets we have to take only positive charges in your solution according to my thinking you are considering the sum as maximum(ith charge or sum + ith charge ) but if ith charge is -ve we dont have to consider it

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

      Thank you, but my question was about why we can't see failed test cases.

      → Reply
  • »
    »
    5 months ago, # ^ |
      Vote: I like it 0 Vote: I do not like it 
    1
5
5 1 -4 2  6

    output should be 11. your code gives 7.

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

      Thank you for provided test case, but what I actually want to know is why failed test cases are not shown in checker output.

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

        I'm not sure about that. Sorry for the wrong reply.

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

This contest is really tricky , I really need to work hard . I wasn't able to think in 3rd problem that from groups of odd's or even sets we can leave negative charges , I was solving like taking the first four charges and finding whether to remove 2nd charge or 3rd one and continuing the process again from remaining ones

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

no offence but why A to D has to be easy speed forces in a div-1 + div-2 round ?

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

    CLIST shows a 1000 rating difference b/w D and E damn

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

    In any contest the starting block consists of quite easy problems, so it's kinda speedforces. Would you like C and D to have been harder?

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

      Yes

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

      C was fine, i guess D should have been in the expert range.

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

      For me at least, C=1400 and D=1800 would have been better, give or take 100 rating points.

      So I suppose C was OK today but D was obviously much easier than it should have been.

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

Div.1+ div.2 = div.3

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

B>C for me

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

Did anyone else have an issue understanding problem D on the mirror sites? The string examples didn't have grids around them. I had to open the original CF problem page.

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

In problem E $$$\mathcal{O}((n + m)k^2/\omega)$$$ passes. 213399890. You can uphack if you want.

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

1159 Rank can I reach Expert (1478 >>> 1600)? I am eagerly waiting for the Rating Changes.

Also, why isn't the CF Predictor Extension working lately? Does anyone have an idea about that?

→ Reply
»
5 months ago, # |
  Vote: I like it +174 Vote: I do not like it

Very cool problems, thanks!

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

    How do you lose 267 points in a single contest and still say "very cool problems"?

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

      The beauty of the problems does not depend on my performance.

      I don't understand the opposite situation when people go to comments after performing poorly and say "It's the worst contest ever". It's not the author's fault that you suck.

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

thank you for this contest!

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

No offense, but did no tester feel that this contest was very unbalanced or that there's no diversity in it? And if they did, why didn't change?

I'm sure high rated people enjoyed the problems, but everyone else got stuck and didn't enjoy as much.

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

I think it's the best contest i have joined in my life Back to specialist

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

Till now best contest for me. For the first time able to solve A,B,C under 30 mins and also the first time to solve D. Although D was easier comparatively.

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

Speedforces ABCD

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

As cyan, i hope to be blue.

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

How can one become a tester for a contest??

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

    Ask authors to participate in testing.

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

      How can i find the authors before testing?

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

        There are few coordinators on Codeforces, their names are known. You can occasionally ask them, and they can help you contact authors of upcoming rounds.

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

How to calculate whether i will get a rating increase or decrease

→ Reply
  • »
    »
    5 months ago, # ^ |
    ← Rev. 2   Vote: I like it +10 Vote: I do not like it

    You can use 'carrot' extension on chrome.

    just add it to your browser and it will show you the expected delta and how was your performance rate in the contest when you open the standing.

    → Reply
»
5 months ago, # |
  Vote: I like it +72 Vote: I do not like it

This contest's problem A is the best a+b problem I've ever seen

→ Reply
»
5 months ago, # |
  Vote: I like it +53 Vote: I do not like it

Rating changes?

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

Rating changes?

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

What's the maximum number iterations can we run in 1 second? My 213380076 for problem D is O(n * (no of factors of n)) The maximum number of iterations run is around 2.5 * 10 ^ 8. But it takes less than 300 ms. How?

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

    I think I did something very similar but my solution is much slower. Is my precomp slow? I think it's $$$N log(N)$$$.

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

      Your precomp is taking more time ig because sample testcase also took 1 sec, in my local machine your code took around 10 seconds, may be RAM block size is the key ig which codeforces use to increase spatial locality

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

    Please explain, how you got the number 2.5 * 10 ^ 8?

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

    after you get your number factored, all remaining operations are rather fast, so I think it is possible

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

When will the rating changes be updated?

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

Anyone, please explain

In problem C why are we taking the maximum of c[i] with 0?

What if we have 1 positive element and the rest as negative?

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

    if there is one positive and rest all are negative then you can simply remove all the elements in front of it and back of it , without adding anything

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

    Then we can leave only that positive element

    Like -1 -5 6 -8 -> -5 6 -8 -> 6 -8 -> 6

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

    you can find the sum of all the positive number on odd indices and same should be done for even

    we are then finding max of them and printing

    in your case when all numbers are negetive suppose -1 -1 -2 5 -9

    we know the ans should be 5

    we know that the sum at odd indices is more now we will choose the number on odd indices that are negetive and remove them -> -3 5 -9 now we will remove -3 and -9

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

i don't know how yesterday i done 2 questions

→ Reply
»
5 months ago, # |
  Vote: I like it -19 Vote: I do not like it

I have an another solution for D. See Here

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

I am new to code forces, why did this contest not give any rating? I am still having 0.

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

    Probably they check if anybody has cheated to remove him from the final standing. And then they will publish ratings updates.

    → Reply
»
5 months ago, # |
  Vote: I like it +36 Vote: I do not like it

This contest's problem A is the smartest way to learn how to print a+b

→ Reply
»
5 months ago, # |
  Vote: I like it +31 Vote: I do not like it

Is it rated?

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

    I can't wait to see cnnfls_csy reach 3500!

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

does anyone know how can we predict our rating changes? Becoz CF-Predictor doesn't seem to be working. EDIT: nvm I read the comment above.

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

is this contest is unrated??

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

As a Romanian, I am delighted to see lots of Romanian rounds lately!

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

Is the round rated...... been waiting for the update since morning

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

Can someone help me figure out where this code gone wrong for problem C 213370130

→ Reply
  • »
    »
    5 months ago, # ^ |
      Vote: I like it 0 Vote: I do not like it 
    Input:
1
5
1 -1 -1 -1 1

Your Output:
1

Correct Output:
2

    You can apply the operation twice at the middle element: $$$[1, -1, -1, -1, 1] \rightarrow [1, -2, 1] \rightarrow [2]$$$

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

Hope everyone get good scores!

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

Is it rated?forces

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

ratings updated when??

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

I cannot afford to have this contest unrated. Please update ratings.

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

May I ask what is wrong in writing the question E like this? Can you explain it or give a wrong example? Thank you very much[submission:213474901]

→ Reply
»
5 months ago, # |
  Vote: I like it +66 Vote: I do not like it

Ratings updated, sorry for the delay.

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

    its okay buddy, dont put too much pressure on yourself!!!

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

    It's okay, buddy, take your time, we don't mind.

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

thank you for the round! problems are all fun

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

Come on guys you can do it 1000 likes target...

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

Can someone please provide a proof of why for $$$c>0$$$, sorted array works in problem F of this contest? It is pretty unintuitive to me.

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