adamant's blog

Codeforces Round #453 (Div. 1 & Div. 2)
By adamant, 7 years ago, translation, In English

Hi everyone!

Missed me? I bet no! In either way, here goes another one round which I dared to spoil by my participation in problemsetting. Welcome to the world of extremely unoriginal problems, awkwardly long and boring statements and trifling jokes in anouncements.

This time round was prepared by Ildar Gainullin (300iq) and me (I'm ashamed to place link of such color here, you know who). We want to thank Vladislav Isenbaev (winger), Konstantin Semenov (zemen), Alexey Shmelev (ashmelev), Ivan Smirnov (ifsmirnov) and Alex Fetisov (AlexFetisov) for testing problems and help in preparation. Also special thanks goes to Nikolay Kalinin (KAN) for his help as coordinator and, of course, MikeMirzayanov for polygon and codeforces.

We hope that you will enjoy the problems, good luck and have fun!

UPD. Also thanks to akvasha for completing our problemset by his problem.

UPD 2. The contest is over, congratulations to winners!

Div. 1:

  1. dotorya
  2. Um_nik
  3. Radewoosh
  4. ainta
  5. dreamoon_love_AA

Div. 2:

  1. UoA_Kaori
  2. noelnadal
  3. mtw
  4. Kroma
  5. Yjsu

Here are editorials.

  • Vote: I like it
  • +959
  • Vote: I do not like it

Comments Comments (150)
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7 years ago, # |
  Vote: I like it +54 Vote: I do not like it

Man! I need such sense of humour!

Anyways, GL and HF.

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    7 years ago, # ^ |
      Vote: I like it -39 Vote: I do not like it

    Guess who is more pr0?me me me. Do you even code bro?

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      7 years ago, # ^ |
        Vote: I like it -24 Vote: I do not like it

      how to get a better Contribution?

      stop commenting or you will get more down vote :)

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7 years ago, # |
← Rev. 5   Vote: I like it +44 Vote: I do not like it

Great Grand Duke Olexandr Kul’kov

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    7 years ago, # ^ |
      Vote: I like it +89 Vote: I do not like it

    I'm sorry but you have some small mistakes.

    It's more correct to write Oleksandr (or Alex if you are lazy to write long words).

    "Great grand" is a bit tautology. But if you mean that Oleksandr is a great guy then maybe it's ok.

    Sources: link, standings of some competitions and wikipedia.

    I hope my comment will help you :)

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7 years ago, # |
  Vote: I like it +12 Vote: I do not like it

Logged in just to upvote you

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7 years ago, # |
  Vote: I like it +22 Vote: I do not like it

When the announcement is so exciting, I bet the contest will be awesome!

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7 years ago, # |
← Rev. 2   Vote: I like it +7 Vote: I do not like it

Welcome to the world of extremely unoriginal problems, awkwardly long and boring statements and trifling jokes in anouncements.

sees some problems from his past contests

Okay I'm bracing myself :D

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7 years ago, # |
  Vote: I like it +69 Vote: I do not like it

Isn't this clashing with Topcoder SRM 726 ?

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7 years ago, # |
  Vote: I like it +27 Vote: I do not like it

how many number of problems will be there?

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7 years ago, # |
  Vote: I like it -55 Vote: I do not like it

FUCK TC SRM. It is clashing with cf round so no way i'm missing it!!!

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7 years ago, # |
  Vote: I like it +40 Vote: I do not like it

hope for no long queues. c:

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7 years ago, # |
  Vote: I like it -48 Vote: I do not like it

awkwardly long problems??? why??? ):

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    7 years ago, # ^ |
      Vote: I like it -11 Vote: I do not like it

    negative comment seriously? do you really like them?:D

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7 years ago, # |
  Vote: I like it +111 Vote: I do not like it

Nooooo... CF and SRM are clashing :/??? Seriously?

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    7 years ago, # ^ |
      Vote: I like it +8 Vote: I do not like it

    Hope either Codeforces or Topcoder will change starting time as soon as possible.

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    7 years ago, # ^ |
      Vote: I like it +45 Vote: I do not like it

    Unfortunately, when we announced this round, there was no SRM on this date on their schedule. When they announced it, it was too late for us to move this round.

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      7 years ago, # ^ |
      ← Rev. 4   Vote: I like it +3 Vote: I do not like it

      Hi, I think there was Data Science Newsletter (of Topcoder) titled "It's Data Science Newsletter Time! SRM this Saturday & the 19th!" in December 9th (10 days ago) and it has a schedule — "SRM 726: December 19 at 11:00 UTC -5". And I remember that the date that announced this round was less than 10 days ago. So I think "When they announced it, it was too late for us to move this round." is not true, isn't it?

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        7 years ago, # ^ |
          Vote: I like it +28 Vote: I do not like it

        I've put Round 453 on the schedule on the 7th. You know, it is the end of the year, we have a lot of rounds and I also have a lot of other things to finish, so wasn't able to move it, sorry about that.

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          7 years ago, # ^ |
            Vote: I like it 0 Vote: I do not like it

          But that's a matter of 90 minutes, was it so hard to put the contest in the 'usual' time (19:30 MSK)?

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            7 years ago, # ^ |
              Vote: I like it +46 Vote: I do not like it

            After SRM we can start no earlier than 21:05 MSK, it is too late. Before it we can start no later than 16:35 MSK, it is too early.

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              7 years ago, # ^ |
                Vote: I like it -22 Vote: I do not like it

              1) So if I understand correctly following events happened in this order: a) you scheduled round on today, b) topcoder announced their SRM date, c) you announced cf date. If that's correct you can't blame them for putting SRM at clashing time.

              2) 21:05 MSK is too late? Many people from Russia participate in SRM at 5:00AM MSK. Or did you mean some other issues?

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                7 years ago, # ^ |
                  Vote: I like it +32 Vote: I do not like it

                1) By scheduling I mean posting it on the public schedule at /contests which propagates to calendars and so on. So I use this word in the same meaning as announcing.

                2) Yes, it is too late. Rounds are made not only for red coders who write contests even at 5:00 AM, but for everybody.

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                  7 years ago, # ^ |
                    Vote: I like it 0 Vote: I do not like it

                  1) In that case I'm sorry for suggesting wrong statements.

                  2) IMHO 21 is perfect time to have a contest. 18 or something can always be troublesome because some people still have courses on university or work. 21 is safely after all such activities and 23 is not too late to end contest (for me, but it depends on a particular guy). And even if it is too late for some people then I guess that having two contests, one at 19MSK and second at 21 MSK is significantly better than one at 18:35 MSK and 19 MSK. Did you try contacting TC to reschedule their SRM since CF was announced first? I guess this is worse for TC than for CF, so if they value what they do they should at least consider this.

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7 years ago, # |
  Vote: I like it -63 Vote: I do not like it

Will the rounds be rated?

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

After retired from ACM-ICPC, I still have something to do with Codeforces, something like becoming a MASTER, just for fun. # Hello the world without training!

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

Intriguing announcement :D !

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7 years ago, # |
  Vote: I like it -8 Vote: I do not like it

Every Third Contest I do on Codeforces becomes unrated due to Server Issues / Test Cases Issues etc. FINGERS CROSSED

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7 years ago, # |
← Rev. 2   Vote: I like it -40 Vote: I do not like it

I request the problem setters to restore the difficulty level of problems, the last 2 contests were a bit easier.

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7 years ago, # |
  Vote: I like it +325 Vote: I do not like it

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7 years ago, # |
  Vote: I like it +53 Vote: I do not like it

adamant gonna be pulling our strings tonight (ahem).

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7 years ago, # |
  Vote: I like it +27 Vote: I do not like it

This was the contribution to Global Warming :) [ LOTS OF TREES ].

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

Why can't I see other's solution to hack? Only thing I see after clicking the solution is Update adobe flash. I use chrome browser.

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    7 years ago, # ^ |
      Vote: I like it 0 Vote: I do not like it

    Have you tried updating Adobe Flash Player?

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

      I too cant hack after locking the problem. I have all the tools installed

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    7 years ago, # ^ |
      Vote: I like it 0 Vote: I do not like it

    maybe flash is disabled in chrome, click the circle near codeforces url and allow flash.

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7 years ago, # |
  Vote: I like it +5 Vote: I do not like it

How to solve Div1 C?

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    7 years ago, # ^ |
      Vote: I like it +28 Vote: I do not like it

    for each i , find smallest j such that [i,j] induced subgraph has a cycle , to do that , build a max spanning tree(weight = min(i , j) for an edge i <-> j) , now its just some path queries.

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

How To Solve Div2 Problem A? Can anyone Explain?

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    7 years ago, # ^ |
      Vote: I like it 0 Vote: I do not like it

    Maybe I can.

    So, you should initialise "int RightCan[submission:33422641] = 0" — the farthest point you can reach. (And you can also reach ALL the points before it — from 0 to RightCan).

    If a[i] <= RightCan — then we can reach the start point of teleport[i]. So, we can change RightCan to b[i], if (b[i] > RightCan). (This if very impotant... becouse otherwise we can decrease RightCan!).

    It's know that a[i] >= a[i — 1], so we don't miss anything.

    And now, if (RightCan < m) you should print "NO\n", otherwise — you can reach your goal and print "YES\n".

    Here is my solution: 33422641

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

      If it is possible. Can you help me, please? In pretest 5 we have:

      11 39
11 19
11 19
11 11
13 18

      In what way can we teleport from 11 to 13? Thank you in advance. In my solution http://codeforces.net/contest/902/submission/33436932 i had wrong answer.

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        7 years ago, # ^ |
        ← Rev. 3   Vote: I like it 0 Vote: I do not like it

        Well, look here:

        3 7

        0 6

        1 2

        4 7

        Your solution gives the answer "NO". But your can reach point 7: 0 -> 4 -> 7.

        port 1: [0 _ 1 _ 2 _ 3 _ 4 _ 5 _ 6]

        ___port 2: [1 _ 2] ___ [4 _ 5 _ 6 _ 7] <-port 3.

        This happens because your looks only on the 2 last teleports. _____________________________________________________________

        And yes, isn't mivael right?

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    7 years ago, # ^ |
      Vote: I like it 0 Vote: I do not like it

    The basic idea behind the solution is you have to find is there any discontinuity between 0 to M.
    To check this Take an array A of size M or greater having initial value 0.
    now take the input [x;y] and do this.
    A[x]+=1;
    A[y]-=1;
    after doing this take prefix sum of array a using A[i]+=A[i-1] form i=1 to M.
    now if any element in array A [ 1 to M ] is equal to 0 except last value then answer will be 'NO' Otherwise 'YES'

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      7 years ago, # ^ |
        Vote: I like it 0 Vote: I do not like it

      Can you explain how prefix sum work in this case?

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        7 years ago, # ^ |
          Vote: I like it 0 Vote: I do not like it

        Take an example.
        N=3 M=5
        0 2 ; a[0]=a[0]+1,a[2]=a[2]-1
        2 3 ; a[2]=a[2]+1,a[3]=a[3]-1
        3 5 ; a[3]=a[3]+1,a[5]=a[5]-1
        after doing this your array will look like
        [1 0 0 0 -1]
        now after taking prefix sum your array will become.
        [1 1 1 1 0]
        no element is 0 except last one so your answer will be "YES" in this case.

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

What's the pretest 3 on C ?

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

How so solve Div2D?

Also, though I was able to solve Div2C , someone please share the logic of it. I saw some people did C quite quickly. That was like fucking awesome.

Was it so easy or some general problem that I don't know?

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    7 years ago, # ^ |
      Vote: I like it 0 Vote: I do not like it

    What I did was for one tree, I kept adding all the children to a single node. And for the other tree, i just remove one child and put under some other parent. Hope this is the right logic though

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      7 years ago, # ^ |
        Vote: I like it 0 Vote: I do not like it

      Hmm seems nice and same as mine. :)

      Although I was able to come with one more logic though a bit late but I believe this will work.

      No two consecutive terms should be not equal to 1.

      I mean to say that no two non unity terms should have distance less than or equal to 1.

      This will suffice as a condition. For designing a tree, your and my logic should work I suppose.

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        7 years ago, # ^ |
          Vote: I like it +4 Vote: I do not like it

        There can be consecutive 1's. The condition is there should be atleast 2 consecutive 2's(or numbers >1)

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          7 years ago, # ^ |
            Vote: I like it 0 Vote: I do not like it

          Yes..That is the thing what I wanted to write. :)

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          7 years ago, # ^ |
            Vote: I like it 0 Vote: I do not like it

          This is what I implemented. Let's see if it is right, lol.

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

How to solve Div2 D/Div1 B?

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    7 years ago, # ^ |
      Vote: I like it -17 Vote: I do not like it

    B. I went for a DFS solution. set the root color and then dfs iteratively coloring the nodes

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    7 years ago, # ^ |
      Vote: I like it +64 Vote: I do not like it

    lets work on
    f0 = 1
    f1 = x
    fi = fi - 1 * x + fi - 2
    answer is fn, fn - 1

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      7 years ago, # ^ |
        Vote: I like it 0 Vote: I do not like it

      Yeah I did exactly the same.

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      7 years ago, # ^ |
        Vote: I like it +4 Vote: I do not like it

      Or use Google: https://en.wikipedia.org/wiki/Fibonacci_polynomials

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        7 years ago, # ^ |
          Vote: I like it +10 Vote: I do not like it

        Usually I self-proclaim myself as someone who knows many things about math, but here you proved the opposite.

        Thanks for the enlightenment you brought ;) I got stuck for an entire hour with D and not even knowing about this ;)

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        7 years ago, # ^ |
          Vote: I like it +8 Vote: I do not like it

        How do you use Google in such problems? I guess that searching "polynomials euclid algorithm small coefficients" would yield no useful result and even on that page you provided I see no useful info (without that mod 2 trick that I still don't understand these Fibonacci polynomials are useless).

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          7 years ago, # ^ |
            Vote: I like it 0 Vote: I do not like it

          You can do it by arbitrary mod. Mod 2 is to keep coefficients below 2. The thing is that if you calculate gcd using some mod and has k steps you will have at least k steps calculating it in rationals.

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      7 years ago, # ^ |
        Vote: I like it +3 Vote: I do not like it

      Using this formula,

      f2 = x*x + 1 = x^2 + 1 and f3 = x*(x^2+1) + x = x^3 + 2x

      Since, the coefficients should be from -1 to 1. So how did you handle this part?

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        7 years ago, # ^ |
          Vote: I like it +24 Vote: I do not like it

        mod2

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        7 years ago, # ^ |
          Vote: I like it 0 Vote: I do not like it

        Instead of mod 2, can we multiply it with (-x) ?

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          7 years ago, # ^ |
            Vote: I like it 0 Vote: I do not like it

          Yes but some higher degree polynomials may contain coefficients outside the range. So you need to multiply with x or -x depending on the current situation.

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      7 years ago, # ^ |
        Vote: I like it 0 Vote: I do not like it

      But the coefficients won't be -1 0 or 1 right?

      (I don't know.. I am probably wrong but please tell me where I am wrong)

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        7 years ago, # ^ |
          Vote: I like it +8 Vote: I do not like it

        Working in means the coefficients are taken mod 2

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

      f3 = x^3 + 2x, however all the coefficents must be in [-1;1]. How did you solve this issue?

      UPD: solved

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      7 years ago, # ^ |
        Vote: I like it +45 Vote: I do not like it

      What? I have no idea why this works :f. This seems like key idea here, but I see no meaning behind it.

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        7 years ago, # ^ |
          Vote: I like it -30 Vote: I do not like it

        It's well known that GCD takes the longest time on fibonacci numbers. This is just an extension of the idea from numbers to polynomials

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          7 years ago, # ^ |
            Vote: I like it +35 Vote: I do not like it

          If we abandon condition about coefficients being from set {-1, 0, 1} then this problem is trivial, I was well aware that without it we can do fi = xfi - 1 + fi - 2... What is tricky here is that reducing mod 2.

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

        if we work on instead of , then this obviously works since fi mod fi - 1 = fi - 2 since x * fi - 1 + fi - 2 mod fi - 1 is obviously fi - 2
        in , this fact still remains true , since degree of fi = degree of fi - 1 + 1 and powers of x are independent over .

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          7 years ago, # ^ |
            Vote: I like it +32 Vote: I do not like it

          I still have no clue about your solution. It is of course true that over , but I see no connection of that fact to Euclid algorithm in and have no idea what this independence has to do with anything.

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            7 years ago, # ^ |
              Vote: I like it +3 Vote: I do not like it

            well fi mod fi - 1 = fi - 2 even in , are you sure you didn't misread the question and thought that coefficients should be {-1,0,1} even for immediate steps?

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              7 years ago, # ^ |
              ← Rev. 2   Vote: I like it +11 Vote: I do not like it

              Let's make it clear what is obvious ans what is not:

              Obvious fact 1: If we define fi = xfi - 1 + fi - 2 over then we have over

              Obvious fact 2: If we define fi = xfi - 1 + fi - 2 over then we have over

              Obviously false statement: If we define fi = xfi - 1 + fi - 2 over then we have over

              Since that last fact is not true, I see no connection of your solution to Euclid algorithm.

              And regarding "are you sure you didn't misread the question and thought that coefficients should be {-1,0,1} even for immediate steps?" — during contest I was solving that wrong question you mentioned (however I am pretty sure you meant "intermediate" not "immediate" :)), but I realized it was not necessary some time ago and still have no clue about it.

              EDIT: Sorry, I made a typo in first version of that post in "obviously false statement"

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                7 years ago, # ^ |
                  Vote: I like it +8 Vote: I do not like it

                ah , i finally get your point , i completely forgot this during contest and just implemented it straight away thinking "its just a div1B , it can't be that hard".
                Let me think about it for a while

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                  7 years ago, # ^ |
                    Vote: I like it 0 Vote: I do not like it

                  The proof isn't that hard. Start from the two polynomials fn, fn - 1. Now do Euclidean algorithm over on these.

                  You can show the following claims by induction. First, all fractions during the process will have odd denominator. Also, the numerators of a polynomial pi(x) you get during the Euclidean algo over will have even numerator if and only if the corresponding coefficients in fi(x) is 0. In particular, all leading coefficients will be fractions with odd numerator and denominator.

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                7 years ago, # ^ |
                  Vote: I like it +6 Vote: I do not like it

                okay here is a much simpler reasoning of why this takes n steps
                Suppose on the contrary , it takes  <  n steps , then for some i ,  fi mod fi - 1 has degree  <  i - 2.
                fi = fi - 1 * (ax + b) + r(x)
                degree of r(x) is less than i - 2
                let fi(x) = ... + pxi - 2 + ...
                and fi - 1(x) = ... + cxi - 2 + ... dxi - 3 + ...
                then we have p = bc + ad in , since each of them are rationals and 2 is obviously a prime , each of these terms exist in as well hence this holds in as well and we have degree of r(x) is less than i - 2 in as well which is a contradiction.

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    7 years ago, # ^ |
    ← Rev. 2   Vote: I like it +2 Vote: I do not like it

    Just try random polynomials: one of degree n and another of degree n - 1 till it works.

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    7 years ago, # ^ |
      Vote: I like it +8 Vote: I do not like it

    Alternatively, you can set P0(x) = 1, P1(x) = x and for i ≥ 2, set

    Pi(x) = x·Pi - 1(x) ± Pi - 2(x)

    for some choice of sign. Exactly one choice of sign works once you fix $P_2(x).$ A computer can verify that this works, but I have no proof.

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

how to solve c and D?

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    7 years ago, # ^ |
      Vote: I like it +3 Vote: I do not like it

    ...... ( f(x) , x+1) -> (x+1 , x ) -> (x,1) -> (1,0)

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      7 years ago, # ^ |
        Vote: I like it -6 Vote: I do not like it

      каждый раз надо находить такой f(x) что f(x) mod (x+1) = x (в нашем случаи ) но я так и не смог написать )

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    7 years ago, # ^ |
      Vote: I like it +4 Vote: I do not like it

    I think Div2C Greedy problem

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      7 years ago, # ^ |
        Vote: I like it 0 Vote: I do not like it

      can you please help me with my code : https://ideone.com/talzy9

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        7 years ago, # ^ |
        ← Rev. 11   Vote: I like it +5 Vote: I do not like it

        test
        5

        1 2 1 2 1 2

        You program is wrong Answer is "perfect"

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          7 years ago, # ^ |
          ← Rev. 3   Vote: I like it +3 Vote: I do not like it

          can you please explain why the answer is perfect in this case?

          EDIT : my bad now i understood thanks a lot for the help ! :)

          btw if i am correct the cases of perfect are those which don't have two consecutive ai > 1 ? if i am incorrect please correct me!

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7 years ago, # |
  Vote: I like it +38 Vote: I do not like it

"awkwardly long and boring statements"

Lol so true

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7 years ago, # |
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i dont understand problem C, output sum(a[i]) E i = 0->h

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    7 years ago, # ^ |
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    That refers to the number of integers you are to print. The summation is nothing but the number of nodes in the tree

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7 years ago, # |
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How to solve div1B?

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7 years ago, # |
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What was the purpose of putting "tree" in title of D? To give a hint for contestants :f?

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    7 years ago, # ^ |
      Vote: I like it +51 Vote: I do not like it

    In Russian is graph instead of tree :/

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7 years ago, # |
← Rev. 3   Vote: I like it +14 Vote: I do not like it

For those who ask about seeing others' submissions/hacks/adobe flash player:

set these settings:

Allow website to use Flash

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    7 years ago, # ^ |
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    i am able to see others submission history but unable to see solution even after locking!

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7 years ago, # |
← Rev. 2   Vote: I like it +8 Vote: I do not like it

Lol, I hacked a few people on Div1A because they did something like cout << ans[i] where ans was of size ~10^5.

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7 years ago, # |
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Nice contest. Couldn't understand C for an hour and after i understand it i solved it in 20 mins. But in general nice.

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7 years ago, # |
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What Div2 (A) pretest 6 ?!

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    7 years ago, # ^ |
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    May be something like.. 3 10 0 9 1 5 7 10

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    7 years ago, # ^ |
    ← Rev. 4   Vote: I like it 0 Vote: I do not like it

    Ooooh, I did break while getting input. My output in pretest 6 was: -- NO NO --

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7 years ago, # |
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This is the way a codeforces contest should be prepared.Kudos to problem setters.

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7 years ago, # |
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Overall, the problems are good. I think ive seen Div2B & A with some changes, the C and D are so challenging. Even though, i almost made it, apparently i didnt. (._.)/, I'm actually really tired but i rushed to join this contest because i wanted to get my expert rating (AHAHAHAH), I ended up doing really sucks, and sloppy (Because of my skill in graph). Lesson I learned in this contest, sometimes you need a rest between contests. :). Merry Christmas !

Update : I think B is easier than A. A is kinda "tricky"

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7 years ago, # |
  Vote: I like it +14 Vote: I do not like it

I've just ruined another div1 contest and now i'm thinking whether it's even possible to come up with an idea for div1B if you've never seen anything similar before -_-

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    7 years ago, # ^ |
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    Well everyone had their own bad day :(. I can relate to what you feel.

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7 years ago, # |
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Anybody anything to E? I can only generate 10^8 pairs as candidates for (sum of ai, sum of ai2) :/

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    7 years ago, # ^ |
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    There will be editorial very soon, please be patient :)

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7 years ago, # |
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Hey, is he a cheater or acts like tourist in the last cs round ? :‑Þ

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    7 years ago, # ^ |
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    Could you explain exactly what makes you think he could possibly be a cheater?

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7 years ago, # |
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I finished coding C/div1 5 minutes after the contest with O(n log n) solution :(

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    7 years ago, # ^ |
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    can you please share your approach for this!

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      7 years ago, # ^ |
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      For each vertex i find the minimum vertex X such that the graph consisting of vertices [Xi i] is bipartite, this can be done using two pointers.

      Now iterate over vertices from 1 to n, for vertex i add 1 to the segment [Xi i] then answer all queries that end in this vertex by finding the sum of elements of the segment that describe the query.

      UPD: I got WA, seems like the tow pointers approach is wrong

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7 years ago, # |
← Rev. 2   Vote: I like it +17 Vote: I do not like it

Good contest, problem D div2 could have been better. but in total, it was way better than what you described.

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7 years ago, # |
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Can't believe I messed up Div2 A :/ Bad day, I guess

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7 years ago, # |
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Can someone hack this , or explain why fit time limit?

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7 years ago, # |
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Such a Great contest! thanks guys XD

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7 years ago, # |
  Vote: I like it +38 Vote: I do not like it

How did this guy submitted after contest ended?

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7 years ago, # |
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Most of it was graph theory.\ I LOVE GRAPHS <3 really enjoyed it , keep up the good work.

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7 years ago, # |
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how to solve DIV-2 D?

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7 years ago, # |
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7 years ago, # |
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In div2B why dfs gives the minimum answer.when to apply dfs or bfs i am weak at it plzz help

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    7 years ago, # ^ |
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    I guess depends on the logic. I thought BFS way. You need to color root of tree at least once. Just color it in first go and this will make all childs of same color. Put neighbours in queue for bfs and go on like this. Link: http://codeforces.net/contest/902/submission/33421572

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    7 years ago, # ^ |
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    You can use both bfs or dfs to solve this problem.
    Keypoint is to note that bfs or dfs produce same result in case of tree.
    Mostly people use dfs in such questions because it is shorter. :)

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7 years ago, # |
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Div 2 problem C 902C - Hashing Trees, Testcase 2 working fine in my computer. But TLE in CF judge 33450049.I'm unable to find any TLE reason.

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    7 years ago, # ^ |
    ← Rev. 3   Vote: I like it +1 Vote: I do not like it

    Undefined behaviour or bug in compiler. The first is more probable. Look at the output of your program.

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7 years ago, # |
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You mentioned "unoriginal problems", evidently I found almost similar problem of div2 A — A. New Year Transportation :D

@adamant: One doubt was this the source of motivation for this problem? :D

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7 years ago, # |
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How to solve Div 2E? I need some implementation details.

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