Vladosiya's blog

By Vladosiya, history, 2 years ago, translation, In English

Hello! Codeforces Round 797 (Div. 3) will start at Jun/07/2022 17:35 (Moscow time). You will be offered 6-8 problems with expected difficulties to compose an interesting competition for participants with ratings up to 1600. However, all of you who wish to take part and have a rating of 1600 or higher, can register for the round unofficially.

The round will be hosted by rules of educational rounds (extended ACM-ICPC). Thus, solutions will be judged on preliminary tests during the round, and after the round, it will be a 12-hour phase of open hacks.

You will be given 6-8 problems and 2 hours and 15 minutes to solve them.

Note that the penalty for the wrong submission in this round (and the following Div. 3 rounds) is 10 minutes.

Remember that only the trusted participants of the third division will be included in the official standings table. As it is written by link, this is a compulsory measure for combating unsporting behavior. To qualify as a trusted participant of the third division, you must:

take part in at least five rated rounds (and solve at least one problem in each of them), do not have a point of 1900 or higher in the rating. Regardless of whether you are a trusted participant of the third division or not, if your rating is less than 1600, then the round will be rated for you.

Thanks to MikeMirzayanov for the platform, help with ideas for problems and for coordination of our work. Problems have been created and written by ITMO University teams: MikeMirzayanov, MisterGu, myav, Gol_D, Aris, senjougaharin, me Vladosiya.

Also many thanks to Kirill22 , daubi , Fortin , Artem_Sukharev , vsinitsynav , yorky , oversolver , majorro , ilya_totl , Undying , olya.masaeva , Kniaz , Golovanov399 , farmerboy , Absyarka , Kavaliro , neeraj_joshi for testing the contest and valuable feedback.

Good luck!

UPD:Editorial

  • Vote: I like it
  • +193
  • Vote: I do not like it

| Write comment?
»
2 years ago, # |
  Vote: I like it +41 Vote: I do not like it

as a tester, I want to say that I've waited for invite so long... and finally got it!

also, expect interesting problems :)

»
2 years ago, # |
  Vote: I like it -6 Vote: I do not like it

All the best everyone hope everyone gets a positive delta

»
2 years ago, # |
Rev. 3   Vote: I like it +3 Vote: I do not like it

hope a good delta positive this time.

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

As a contestant, I want to say good luck to all contestants

»
2 years ago, # |
  Vote: I like it +30 Vote: I do not like it

Finally Dream come true!! . Now i can finally give div3 as an unrated participant !!. It took 1 year for this moment.

»
2 years ago, # |
  Vote: I like it +29 Vote: I do not like it

»
2 years ago, # |
  Vote: I like it 0 Vote: I do not like it

div 3 and div 4 are good contests for newbie participants

»
2 years ago, # |
Rev. 2   Vote: I like it -27 Vote: I do not like it

六国は、軍が破壊されていない賄賂秦賄賂秦と破壊の方法の電力損失で良い戦いの欠点はまた、六国は、賄賂秦のはい、強い支持の損失を買収するために互いの速度を失ったと言った賄賂秦の欠点も攻撃して外に取ることは秦が得ると勝利と得るより邑大実際に百倍の死と敗北と死実際にまた百倍の偉大な悩みの領主は最初の祖父 嵐 霜露カット考えるには戦争ではありません初代の祖父は小さな土地を持つために茨を切り、その子孫はそれを草の浪費と見て、今日は5都市、明日は10都市を切り、秦軍が来る間、安心して寝て四領を眺めることができたのです燕・趙の王は、秦に賄賂を贈らず、自分の国を守る遠大な戦略を持っていたので、燕は小国ではあったが、後に滅亡した三国志が秦に付かず、刺客もいないのであれば、勝敗の数、生存の理由も秦に比べれば簡単には測れないかもしれません世界から六国崩しの話を取り上げると、また六国の下になる

»
2 years ago, # |
  Vote: I like it -32 Vote: I do not like it

All the best everyone . Hope all of you get a positive delta

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

    why so downvotes "."?

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

      Dont know . Maybe they didn't like my well wish. Anyways my bad.

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

        All those downvotes are because of you're wishing for positive delta (Covid variant) :)

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

          Ooh . Should I've written plus rating then it would have been the upvotes. Correct?

»
2 years ago, # |
  Vote: I like it +4 Vote: I do not like it

First unrated div 3. Yay:)

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

    disadvantages of being expert.That's the reason i am still specialist.

»
2 years ago, # |
  Vote: I like it 0 Vote: I do not like it

Div3 round yayy !! Is the round really meant for Div3 when we can see no tester who is <1600 ...

Also what is the point in including so many high rated testers and not a single <1600 tester ?

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

    Obviously to make an unbalanced round :D (no offence)

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

Hope good practice and new colors for all rated participants

»
2 years ago, # |
  Vote: I like it +1 Vote: I do not like it

!Unrated for me too :D

»
2 years ago, # |
  Vote: I like it +9 Vote: I do not like it

i am always ready for the div3 with my cup of tea

»
2 years ago, # |
  Vote: I like it +13 Vote: I do not like it

I didn't participate in 5 rated rounds and my rating is below 1600 can I participate??

»
2 years ago, # |
  Vote: I like it 0 Vote: I do not like it

I wish that every Chinese student can get good grades in Gaokao!

»
2 years ago, # |
  Vote: I like it 0 Vote: I do not like it

how to do E?

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

    Try to think about case : how does answer change if we pick such $$$(i,j)$$$ that $$$(A_i$$$ $$$mod$$$ $$$k)$$$ $$$+$$$ $$$(A_j$$$ $$$mod$$$ $$$k)$$$ $$$>=k$$$ .

    For example : $$$k=3$$$

    $$$A:{1,2,4,5}$$$

    matching $$$(1,5),(2,4)$$$ gives answer $$$4$$$ and matching $$$(1,4),(2,5)$$$ gives $$$3$$$

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

    for each value a[i], a[i]/k will always be there in the total answer. So, we can add a[i]/k for all i. Then, in another array we store a[i]%k. Now, the maximum sum of two of the remainders of a[i] and k is 2k-2. And (2k-2)/k is 1. So we have to find the number of pairs that we can form (from the remainders) such that their sum is greater than or equal to k. We can do this using greedy + two pointers. My solution — https://codeforces.me/contest/1690/submission/159852372

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

I think the authors are very much interested in permutation graph this is 4th instance in last one month I find same kind of question F

https://atcoder.jp/contests/abc247/tasks/abc247_f

https://codeforces.me/contest/1678/problem/E

https://codeforces.me/contest/1670/problem/C

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

    If you have some more basic questions of this concept please do share. I didn't knew about this earlier, that such a topic exists. Thanks.

»
2 years ago, # |
  Vote: I like it +1 Vote: I do not like it

How do you solve F and G?

»
2 years ago, # |
  Vote: I like it +1 Vote: I do not like it

How to solve the edge case for F while solving for LCM of each cycle?

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

    What edge case?

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

    Yeah, I got all the cycles and tried to get all the number of moves for each cycle such that all the letters get matched to the correct locations. But I had no idea how to go on from there without brute force.

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

      I think brute force works? Constraints are low enough that for each cycle you can check how many rotations are needed to return this cycle to it's original position (and you can take the LCM of all this)

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

        what happens if there are multiple possible rotations needed to return the cycle to its original position?

        • »
          »
          »
          »
          »
          2 years ago, # ^ |
            Vote: I like it +2 Vote: I do not like it

          we take the first time the cycle returns to its original position as there is no needs to go further

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

          All future rotations are multiples of the first.

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

            Could you please clarify? Edit: Nevermind, I've understood. Thanks

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

              let's say you have string "abab".The first time this string comes to it's original state after rotations is after 2 rotations.

              rotation 1 : baba
              
              rotation 2 : abab

              So from here you can figure out that this string repeats itself after every 2 rotation. Now to get the answer you simply need to find this minimum rotation required for each cycle.

              let's say you have got cycle of "aba", "bba", "abab", "aaa" and each of them repeats itself after 3, 3, 2, 1 rotations respectively. So, the answer for this case would be lcm(3, 3, 2, 1) = 6

              you can checkout my implementation

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

              ^ Ashish mostly covered it. Essentially if it takes k operations to return the string to it's original position, then it will take another k operations to do the same thing again.

              Therefore the string is in its original orientation at time k, 2k, 3k, etc. You only care about k, because all other rotations are just multiples of k.

              You then need to find some number that is a multiple of all other original orientations, and therefore we arrive at our lcm idea

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

    For individual cycle you need to find number of operations after which string will repeat with brute force and then take LCM.

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

    try to check for pattern, like if cycle string is abab you take the lcm of answer with 2(not 4)

»
2 years ago, # |
  Vote: I like it -23 Vote: I do not like it

Speedforces

»
2 years ago, # |
Rev. 2   Vote: I like it +1 Vote: I do not like it

ones who solved C are more than ones who solved B !!

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

    I took more time in A , than (B+C+D) combined xD

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

    Yes! Sometimes $$$B$$$ is more indirect and confusing than $$$C$$$. I too spent slightly more time on problem B than C:

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

      I spent 6 minutes on A, vs 4 minutes on B and 3 minutes on C..

»
2 years ago, # |
  Vote: I like it 0 Vote: I do not like it

The pedestal consists of 3 platforms for 2-nd, 1-st and 3-rd places respectively.
it's the first time in cp history to see the above misleading description ,why it can't be 1-st ,2-nd and 3-rd!

»
2 years ago, # |
Rev. 4   Vote: I like it +3 Vote: I do not like it

For problem A, can the problem statement use $$$h_1, h_2, h_3$$$ instead of $$$h_2, h_1, h_3$$$ ? Putting some formal definition helps too like

  • $$$h_1 + h_2 + h_3 = n$$$
  • $$$h_3 < h_1 < h_2$$$
  • $$$h_i > 0$$$ $$$(1 ≤ i ≤ 3)$$$
  • $$$h_2$$$ is minimized

Took me a while to understand the problem statement itself

»
2 years ago, # |
  Vote: I like it 0 Vote: I do not like it

help me solve E,
if it is greddy then write proff of correctness
or give me some tips on how to think on this kind of question

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

    Instead of maximizing values, we want to "minimize" loss. Notice that if we group 2 items into the same package, their sum might not be divisible by $$$k$$$. So we can see here some "profit" are lost (which is the remainder of $$$(a_i + a_j)$$$ $$$\text{mod}$$$ $$$k$$$. Therefore we want to pair items in such a way so our profit loss are minimized.

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

      yep. It was all about minimizing waste.

  • »
    »
    2 years ago, # ^ |
    Rev. 4   Vote: I like it 0 Vote: I do not like it

    For each good it is sure that u can get a[i]/k.Then you still have to deal with n a[i]%k. Use f[j] to record the number of a[i]%k that == j. If u can find two things that add up over k,ans++. Even the biggest two goods,still 2k-2,and after /k,it is 1. 159835536

»
2 years ago, # |
  Vote: I like it 0 Vote: I do not like it

Not able to pass E's Test case 3. Anybody has a hint??

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

    Int overflow. Use ll ans = 0; instead of int ans = 0;.

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

    My solution is firstly for each $$$i$$$, add $$$a[i]/k$$$ to the answer, then reduce $$$a[i]$$$ to its remainder divided by $$$k$$$.

    Then for example with $$$k = 6$$$ : we want to pair an $$$a[i] = 4$$$ with something $$$\geq 2$$$ (so not $$$1$$$) to get more cost, this can be done with 2 pointers

    Edit : nevermind, got hacked :d

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

      I did it with binary search on maps

»
2 years ago, # |
  Vote: I like it 0 Vote: I do not like it

why is this giving WA?? what's test 2 :( code

»
2 years ago, # |
  Vote: I like it 0 Vote: I do not like it

How to solve E ?

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

    we need to maximize floor((a[i] + a[j]) / k)

    floor((a[i] + a[j]) / k) = a[i] / k + a[j] / k + (a[i] % k + a[j] % k) / k -> (1)

    => we need to maximize (1)

    a[i] / k and a[j] / k are constants, so we cannot maximize them. Therefore, they directly contribute to the answer.

    => we only need to maximize (a[i] % k + a[j] % k) / k

    The above expression can be maximized when the numerator is maximum since the denominator is constant.

    => now we need to maximize (a[i] % k + a[j] % k). This can be done by an approach similar to two-sum where we try to pair the smallest remaining element with the largest remaining element such that their sum is >= k (because only then the sum can contribute towards the answer)

»
2 years ago, # |
  Vote: I like it 0 Vote: I do not like it

Hey guys, could anyone of you help me out real quick? Speaking of problem F...

This is my submission: 159858692. I count the lengths of all cycles and see whether this cycle really changes anything in the string, if so — I include it while LCMing all valid cycles.

What did I miss here? I am thinking of some cycles of substrings like "baba". Is that the case or anything else?

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

    "baba" will become equal to orginal string after 2 rotations and not 4

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

      Yeah thats what I was thinking about, thanks. Any way how I could implement it in my code?

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

        The time constraints allow you to rotate the string untill it becomes equal to original.Otherwise ,for a linear time solution you can implement it using LPS(longest prefix suffix) array.

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

          Alright, thanks again, I'll look into it!

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

            Or you can just use: int period = (str + str).substr(1,2*str.size()-2).find(str) +1;

            Above code works in O(n) time.

            • »
              »
              »
              »
              »
              »
              »
              2 years ago, # ^ |
              Rev. 4   Vote: I like it 0 Vote: I do not like it

              How would that work? I guess I apply it incorrectly: 159869936.

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

                Sry my mistake there should be 2*str.size()

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

                  It still seems to be failing if I use correct string for that. Check out my code in the previous comment, please.

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

          but it s not written that sum of n over all test cases will not exceed 200.Does that mean that in a single input set, there could be 1000 inputs where n=200?

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

    Yes. The periodic can be something like abcabc for this case, you need to take the length 3 instead of 6 into account

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

      I see, thanks. Any way how I can insert this check in my code?

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

        You can brute force the length of the periodic substring. For a fixed periodic with a length $$$len$$$, we can check for every substring with a length $$$len$$$ are the same substring. So we can just brute force the $$$len$$$ value (make sure that $$$len$$$ is a divisor of the cycle length as well)

        This will runs in $$$O(n^2)$$$. Since $$$n$$$ is small enough, we will be able to do so

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

          Got it, thank you for your time!

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

          This will run in $$$O(n \cdot cnt(n)) \approx O(n \sqrt[3]{n})$$$ where $$$cnt(n)$$$ — number of divisors of $$$n$$$.

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

          ...

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

        you can just brute force on all the factors of the length of the cycle to check the periodicity of each factor and consider the smallest one

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

    Ye that's about it. If you have a -> b -> a -> b cycle then it's rotational value is 2 not 4.

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

      Why the cycle is 4, not 2?

      abab [Initial String] baba abab [Returned to initial string after 2 rotation]

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

        That is exactly what barun511 says :)

»
2 years ago, # |
  Vote: I like it 0 Vote: I do not like it

Does the time taken to solve questions matter in div 3 & div 4 contests?
Like if 2 people solve the same number of questions, do they get the same rank or does the one who took less time to solve them get a higher rank?

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

    The one who spent less time gets a higher rank.

»
2 years ago, # |
  Vote: I like it 0 Vote: I do not like it

If the equal cycles of a string are its periods then what is KMP made for???
I remember using this above rule in an atcoder contest, but I forgot it today due to knowing what KMP does

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

EDIT : Got the failing test case. Thanks!

Can someone tell me why my code : https://codeforces.me/contest/1690/submission/159863108 is giving index out of bounds, also do tell the test case that is failing. Thanks!

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

    In submission, it is written " 'out of bounds' on the line 128". Probably when rem[k-i] is empty

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

    Assuming that i == k-i then, you might reach a case where the size of the vector only consists of 1 element and you're popping back it twice (for example where $$$i$$$ and $$$k-i$$$ is equal to 0)

»
2 years ago, # |
  Vote: I like it +1 Vote: I do not like it

Nice round! and very educational.

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

    You have directly assumed that the number of members in the cycle is the number of iterations it will take to loop back to initial value or 1 in the case of similar characters in the loop. But suppose take the case abab in this it will take 2 iterations only. abab --> baba --> abab.

    What you actually needed to do here was find if the string has a repeating pattern which you can do in two ways as pointed by many people — 1. Using Longest Prefix Suffix — O(n) time complexity 2. Or rotating the array till it is equal to its initial value — O(n^2)

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

    You haven't considered if a cycle has string like abcabc, when this is the case, the length of the cycle is not 6 but 3

»
2 years ago, # |
  Vote: I like it +11 Vote: I do not like it

Emmm....Why I am an official participant with rating 1601?!?

»
2 years ago, # |
  Vote: I like it 0 Vote: I do not like it

For problem F I have counted length of all cycles and also the stored the text string formed for each cycle and then simply use Longest prefix suffix logic to find if there is a repeating pattern so as to find min iterations in which cycle loops back to initial value and finally I have taken lcm of all these values.

But still it is giving WA. Can anyone please help me figure out what's wrong in my approach? :(

Link to my solution

»
2 years ago, # |
  Vote: I like it +1 Vote: I do not like it

logicforces

»
2 years ago, # |
  Vote: I like it 0 Vote: I do not like it

Hi! Why does this submission 159869794 get AC, but this 159757251 — WA?

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

    This kind of bugs is one of nightmares in java. Remember that ArrayList returns Integer, not int. You should use equals instead of ==, when you are comparing Integer with Integer. In your AC code, you compared Integer with int, so it was fine.

»
2 years ago, # |
  Vote: I like it 0 Vote: I do not like it

How to solve D??

I tried to iterat through all substrings of length K and count the 'W' cahr and every time update the ans with ans=min(ans,cnt)

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

    It can be solved using prefix sum. You basically count up to each index how many 'B' are there and store them in an array, the loop through this prefix array and check in a subarray of length k how many 'B' are there. I'm not really good at explaining so you can check my code and ask any questions if you want

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

      It's just like when you asked to give the sum of elements from L to R but here the number of 'B' and update answer with k — number of B?

»
2 years ago, # |
  Vote: I like it +4 Vote: I do not like it

image

B WAAAAAA

»
2 years ago, # |
  Vote: I like it 0 Vote: I do not like it

In problem F, how do I find cycle for an alphabet?

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

    If you want to find cycles in permutation then you can use DSU.

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

    dsu works but is kind of an overkill. I usually go for a dfs-like iteration and keep visiting the next element until I reach the beginning from where my iteration started. I also keep a bool array to not run a specific cycle twice

»
2 years ago, # |
  Vote: I like it 0 Vote: I do not like it

I'm gonna become blue now, thx

»
2 years ago, # |
  Vote: I like it 0 Vote: I do not like it
»
2 years ago, # |
  Vote: I like it 0 Vote: I do not like it

Is there a possibility that the answer for F exceeds $$$10^{18}$$$?

»
2 years ago, # |
  Vote: I like it 0 Vote: I do not like it

can anyone tell me why my code giving WA https://codeforces.me/contest/1690/submission/159887831

»
2 years ago, # |
  Vote: I like it 0 Vote: I do not like it

My Rating was 973 initially, still this contest is showing unrated for me. Why so ?

»
2 years ago, # |
  Vote: I like it +7 Vote: I do not like it

How to solve G

»
2 years ago, # |
  Vote: I like it 0 Vote: I do not like it

Can someone tell me why f is wrong in the 100th of the second example?Thanks you!

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

    that test is 9 cbbbcbccb 9 5 6 8 4 3 1 2 7 which contains a cycle of index 5-2-8-4 cbcb ,it justs need 2 steps instead of 4 so the answer is 6 not 12

»
2 years ago, # |
  Vote: I like it +10 Vote: I do not like it
»
2 years ago, # |
  Vote: I like it 0 Vote: I do not like it

Will the editorial be released for this?

Its been around 13 hours since its completion.

»
2 years ago, # |
  Vote: I like it 0 Vote: I do not like it

After giving the contest, why am I still unrated?? This was my first contest.

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

    Due to the hacking phase that was completed just a few moments ago. I guess you will get your ratings in a while!

»
2 years ago, # |
  Vote: I like it 0 Vote: I do not like it

wHeRE EdiToRiaLl?

»
2 years ago, # |
  Vote: I like it +1 Vote: I do not like it

why it is showing unrated till now

»
2 years ago, # |
  Vote: I like it 0 Vote: I do not like it

I think given explanation of example in E is wrong. Please correct me, if I am missing something.

Example is, n=6,k=3, weights of goods a=[3,2,7,1,4,8]

We have to pack them into n/2 packages, ie. two goods in each package, and such that total cost is minimised, where cost is [weight_of_package/k], (ROUNDED DOWN).

So, "according to me", they should be packed into these packages: [7,1] (cost=8/3 = 2), [3,2] (cost=5/3 = 1), and [4,8] (cost=12/3 = 4)

So, cost should be 2+1+4 = 7. (This is the minimum I can get)

But in example the minimum cost given is 8. How ? Or there's some caveat in my approach ?

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

    The problem is a maximization problem, not minimization.

»
2 years ago, # |
  Vote: I like it 0 Vote: I do not like it

I had a doubt. Is this contest unrated. My rating is less than 1600 and I have given 5 rated contests before.Have the ratings been applied yet?

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

why weak pretests on E.

»
2 years ago, # |
  Vote: I like it 0 Vote: I do not like it

First 3-digit placement, yay! :D Thank you for this contest! <3

»
2 years ago, # |
  Vote: I like it +6 Vote: I do not like it

This is my submission for E, why getting TLE, complexity seems to be O(n+k^2) to me which should be fine, https://codeforces.me/contest/1690/submission/159917329

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

    It's $$$O(T(N+K^2))$$$ which cannot pass

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

      But the constraint for K is 1000 , so K^2 should give 10^6 which is enough I think , considering it is given sum over all test case will not exceed 2*10^5

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

        There's no constraint on the sum of $$$K$$$ over all the test cases.

»
2 years ago, # |
  Vote: I like it 0 Vote: I do not like it

Can someone plz tell me why is this code failing at test 2? "problem B" https://codeforces.me/contest/1690/submission/159826598

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

    Consider the case, a=[6 5 7] and b=[0 0 2]. Here, your logic will give output as yes as it first compares for 6,5 and then for 5,7 but the correct output shall be No. Understand why this problem arises and Modify your logic to correct it.

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

    The first mistake syntax error you are doing is that (if(su[i]==su[i-1]) continue;). this condition can give you index out of bound for i=0, and accessing su[0-1] = s[-1].

    The test case where your code is when you need to compare the difference of current ith to greater previous than last one. i.e 1 4 5 1 2 5 1 0 0 0

    Expected : NO OUTPUT: YES

»
2 years ago, # |
  Vote: I like it +1 Vote: I do not like it

still not updated the ratings ..... it's been more than 17 hours since it got finished.

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

    same problem.. i dont know why but for both of us the round was unrated

»
2 years ago, # |
  Vote: I like it +6 Vote: I do not like it

My solution for F was accepted in Python but not in PyPy3

ಥ_ಥ

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

Attention!

Your solution 159836981 for the problem 1690F significantly coincides with solutions Pretest2/159836252, Ksathwik03/159836981. Such a coincidence is a clear rules violation. Note that unintentional leakage is also a violation. For example, do not use ideone.com with the default settings (public access to your code). If you have conclusive evidence that a coincidence has occurred due to the use of a common source published before the competition, write a comment to post about the round with all the details. More information can be found at http://codeforces.me/blog/entry/8790. Such violation of the rules may be the reason for blocking your account or other penalties. In case of repeated violations, your account may be blocked.

I have referred and used the template provided by gfg (https://www.geeksforgeeks.org/minimum-rotations-required-to-get-the-same-string-set-2/) which has been published before the start of the contest ,to solve the problem of of minimum rotations to get back the original string i did not use any unfair means or copied the solution you can check our both code they are completely different except for that rotation string part. [user:https://codeforces.me/profile/MikeMirzayanov] i request you to please check and do the needful :).

I would like to mention that the account with whom i was (plagiarized)[https://codeforces.me/profile/Pretest2] , his rating got increased whereas my rating wasn't

»
2 years ago, # |
Rev. 3   Vote: I like it 0 Vote: I do not like it

I am amazed how many participants are discussing their "missed" rating change instead of solving unsolved problems.

$$$P.S.$$$ It's simple, if there was no announcement that round have became unrated, you should just wait a bit.

»
2 years ago, # |
  Vote: I like it 0 Vote: I do not like it

my rating is less than 1600 so if i am right this round should be rated for me but why is this contest not showing in rated graph? and my rating too remained unchanged.

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

    The ratings have not been updated yet. You will see your rating's changes only after they have been updated.

»
2 years ago, # |
  Vote: I like it +1 Vote: I do not like it

Rating update is slow(;′⌒`)

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

    I reloaded many times with the expectation of seeing my positive delta. But it didn't appear :(

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

      Just use CF Predictor

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

        Carrot is also good

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

          Wait so I just added Carrot, and it shows a different predicted rating change, much lower than CF Predictor. Why so?

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

            Carrot is normally much more accurate than CF predictor. So you should go with the rating that carrot predicts

»
2 years ago, # |
  Vote: I like it -10 Vote: I do not like it

wth !! It's unrated for everyone . You can see in your graph in the profile ,change to all contests .

»
2 years ago, # |
  Vote: I like it +1 Vote: I do not like it

May I know will there be any Editorial for the contest. It is my first contest and I only solve 4 lol~ It is a fun and beginner-friendly contest.

»
2 years ago, # |
  Vote: I like it 0 Vote: I do not like it

When will the ratings get updated?

»
2 years ago, # |
  Vote: I like it -21 Vote: I do not like it

Hey Vladosiya, MikeMirzayanov

I just recieved a message saying that my solution in the last div.3 contest coincided with Time_to_pass. I'm mistakenly accused of cheating in #797 (Div. 3).

I swear that I didn't cheat in the contest, and all the codes in this contest are 100% written by me. Both were my IDs only. I tried solving it from another ID to avoid penalty. I know it was not never a good habit. I will not be doing these silly things onwards. I apologize for my mistake. I have given around 30 contests and this is the first time I have done this. Please help me. [I can give proof if needed about the IDs ownership]

»
2 years ago, # |
  Vote: I like it 0 Vote: I do not like it

Who else got bamboozled by F and did union find only to get a wrong answer and not knowing why Only after contest, then realised its a directed graph and uf cannot be applied here

»
2 years ago, # |
Rev. 2   Vote: I like it +4 Vote: I do not like it

Dear MikeMirzayanov,

Sir my rating get changed even though it should be unrated for me can you check this as it will be unfair for others.

»
2 years ago, # |
  Vote: I like it +3 Vote: I do not like it

hello admins I have just received a message saying my solution 159822431 for the problem 1690B significantly coincides with solutions 7878797/159821282.It was unintentionally because I have used ideone.com and I am totally unaware of that because till now I have given few contests on Codeforces using VScode and this was the first time I have used ideone.com because of some updation required in vscode. And I have checked 7878797 user id recently and I have found that this id is having its rating skipped in its previous contest also and one more thing is that this id have used different templates of code in every question, these two things are enough to know that user id 7878797 is a cheater and have copied my solution of 1690B which was totally written by me. So, I am totally innocent and hence this is my humble request to give me my ratings back and now onwards I will totally follow the instructions of which I was unaware previously. Thank you

»
2 years ago, # |
  Vote: I like it 0 Vote: I do not like it

Hi Admin, ( Vladosiya , MikeMirzayanov )

I received a message regarding the contest Codeforces Round 797 (Div. 3) saying that: my solution for the 1690E - Price Maximization coincides with about 11 other people. - I'm a newbie here and I don't know many people, so cheating/copying is unethical and impossible for me. I've realized what mistake I did. I use ideone.com and other open judges (for this contest I used ideone) to test my solution on sample cases, didn't know that people could copy down answers/solutions from ideone.com. I know this is a clear rules violation as per unintentional leakage, however, I was totally unaware of it. I'm really sorry about this and I'll make sure to use only local and private testing systems in the future. I went through the solutions of the people mentioned and noticed that they had copied the code, with some modifications, which is unfair for me. Can you please look into this and return my ratings, I had a decent positive delta. It'll really boost my morale. Thanks.

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

    you will get more positive rating changes in the future again. it was a mistake and you got the lesson (not using public online ides). It is not a big deal, just forget about it.