jqdai0815's blog

IAEPC Preliminary Contest (Codeforces Round 999, Div. 1 + Div. 2)
By jqdai0815, history, 5 weeks ago, In English

Hello, Codeforces!

We are pleased to invite you to IAEPC Preliminary Contest (Codeforces Round 999, Div. 1 + Div. 2).

The Preliminary Contest is a rated contest for Div. 1 + Div. 2, taking place on Jan/20/2025 17:35 (Moscow time). The problems for this round were prepared by jqdai0815 and orzdevinwang.

The top 50 contestants at least 18 years old will be invited to participate in the onsite finals. We will cover the travel expenses for onsite contestants. The finals are scheduled to take place in CUHK from February 27 to March 2, 2025.

The prizes for first place, second place, and third place of the onsite final are 10000, 5000, and 3000 USD.

More prizes and detailed information will be announced soon. You can visit International AI Elite Programming Contest for information.

We would like to thank:

The score distribution is as follows: $$$500 - 1000 - 1500 - 1500 - 2000 - (2000+2000) - 3000 - (3000+5000) - 4500$$$.

We hope you enjoy this round. Good luck and have fun!

UPD 1: Editorial

UPD 2: Congratulations to the top 10!

  1. jiangly (Congratulations on being jiangly!!!)
  2. tourist
  3. gamegame
  4. Benq
  5. ecnerwala
  6. arvindf232
  7. ksun48
  8. Egor
  9. potato167
  10. Um_nik (Congratulations on being the only one to solve Problem I!!!)

For the top 50 contestants, we will contact you soon for onsite participation.

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

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5 weeks ago, # |
  Vote: I like it +3 Vote: I do not like it

Auto comment: topic has been updated by jqdai0815 (previous revision, new revision, compare).

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5 weeks ago, # |
  Vote: I like it +124 Vote: I do not like it

The onsite finals are during EUC :(

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    5 weeks ago, # ^ |
      Vote: I like it +39 Vote: I do not like it

    It's also clash with ICPC Asia Pacific Championship...

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      5 weeks ago, # ^ |
        Vote: I like it +21 Vote: I do not like it

      As it stands now it seems like $$$\geq 4$$$ of the top 50 are affected by the clashes... Petr and Egor are both EUC judges (I don't know how stringent the requirements are for being present at EUC, but it seems at least really unfortunate), while (correct me if I am wrong) tkacper and me are both contestants at the EUC.

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      4 weeks ago, # ^ |
        Vote: I like it +2 Vote: I do not like it

      Since I am also a participant in APC, I am hoping for a change in the competition schedule.

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5 weeks ago, # |
  Vote: I like it +83 Vote: I do not like it

Rooting for jiangly to reach 4000!!

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5 weeks ago, # |
  Vote: I like it -66 Vote: I do not like it

My Goal for This Contest

Spoiler
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5 weeks ago, # |
← Rev. 2   Vote: I like it +10 Vote: I do not like it

jqdai0815 and orzdevinwang ORZ I'm excited to see their problems !

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5 weeks ago, # |
  Vote: I like it +89 Vote: I do not like it

Nice to see a new competition with onsite finals, but it doesn't seem like a good idea to set the qualification round for weekday.

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5 weeks ago, # |
  Vote: I like it 0 Vote: I do not like it

/jqdai

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5 weeks ago, # |
  Vote: I like it +4 Vote: I do not like it

The round for jiangly to reach tourist!

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5 weeks ago, # |
  Vote: I like it 0 Vote: I do not like it

The round where jiangly becomes tourist?

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5 weeks ago, # |
  Vote: I like it +27 Vote: I do not like it

Congratulations for putting a Div. 1 + Div. 2 round on monday

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5 weeks ago, # |
  Vote: I like it +1 Vote: I do not like it

jiangly might hit tourist

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5 weeks ago, # |
  Vote: I like it -20 Vote: I do not like it

Really Curious about it !!

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

jiangly will be jiangly

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5 weeks ago, # |
  Vote: I like it 0 Vote: I do not like it

The prizes are not worth it

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5 weeks ago, # |
  Vote: I like it 0 Vote: I do not like it

will jiangly hit 4000??!

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5 weeks ago, # |
  Vote: I like it +113 Vote: I do not like it

If you want to host somehow important round, like a qualifying contest for something, isn’t it generally better to host it during a weekend?

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5 weeks ago, # |
  Vote: I like it 0 Vote: I do not like it

Contest 999! Penultimate contest to 1000!

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

For casual users just participating will this be a rated contest?

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    5 weeks ago, # ^ |
      Vote: I like it +1 Vote: I do not like it

    Yes, you will be rated. Div1+2 will be rated for everyone. (unless unrated participation is applicable)

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5 weeks ago, # |
  Vote: I like it +2 Vote: I do not like it

As a first-time tester, I tasted this round

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5 weeks ago, # |
  Vote: I like it 0 Vote: I do not like it

cool zak round!

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5 weeks ago, # |
  Vote: I like it +1 Vote: I do not like it

If I would be system admin, I would swap round #999 with round #1000.

I would make round #1000 a grand round ( Div 1 + 2 ). because its a big milestone.

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5 weeks ago, # |
  Vote: I like it +1 Vote: I do not like it

Rooting for jiangly :)

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5 weeks ago, # |
← Rev. 2   Vote: I like it -71 Vote: I do not like it

I made a mistake.

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5 weeks ago, # |
  Vote: I like it 0 Vote: I do not like it

This contest will rated or not ?

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5 weeks ago, # |
  Vote: I like it +11 Vote: I do not like it

Score Distribution ??

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5 weeks ago, # |
  Vote: I like it 0 Vote: I do not like it

Score distribution?

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5 weeks ago, # |
  Vote: I like it 0 Vote: I do not like it

jiangly will be the new title for 4000

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5 weeks ago, # |
  Vote: I like it 0 Vote: I do not like it

where is the score distribution ? and New rank jiangly will be adedd ?

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5 weeks ago, # |
  Vote: I like it 0 Vote: I do not like it

Auto comment: topic has been updated by jqdai0815 (previous revision, new revision, compare).

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5 weeks ago, # |
  Vote: I like it -8 Vote: I do not like it

I think, there must be problems on probability since it will be an AI based round!

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5 weeks ago, # |
  Vote: I like it +25 Vote: I do not like it

So who is Jiangqi Dai, jqdai0815, djq_cpp or djq_fpc?

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5 weeks ago, # |
  Vote: I like it +14 Vote: I do not like it

score distribution ?

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5 weeks ago, # |
  Vote: I like it 0 Vote: I do not like it

All eyes on jiangly!

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5 weeks ago, # |
  Vote: I like it +10 Vote: I do not like it

The score distribution will be announced soon. When is 'soon'?

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5 weeks ago, # |
  Vote: I like it +6 Vote: I do not like it

What about Score Distribution?

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5 weeks ago, # |
  Vote: I like it -6 Vote: I do not like it

Auto comment: topic has been updated by jqdai0815 (previous revision, new revision, compare).

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5 weeks ago, # |
  Vote: I like it +48 Vote: I do not like it

9 problems, 2 subtasks with one task having a score of 8000, SCARY !!

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5 weeks ago, # |
  Vote: I like it 0 Vote: I do not like it

Codeforces Round (999) just proved that the scoring system can make or break a contest. What a round!

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5 weeks ago, # |
  Vote: I like it 0 Vote: I do not like it

The first rated contest has this number of problem ever.

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5 weeks ago, # |
  Vote: I like it 0 Vote: I do not like it

The testing of the previous round is not complete yet (and not even close). Is it going to affect this round?

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5 weeks ago, # |
  Vote: I like it -36 Vote: I do not like it

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5 weeks ago, # |
  Vote: I like it +13 Vote: I do not like it

Perhaps more than half of the top 50 participants will be unber 18 :(

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5 weeks ago, # |
  Vote: I like it 0 Vote: I do not like it

Why can only people over 18 go to the final?

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5 weeks ago, # |
  Vote: I like it 0 Vote: I do not like it

Good luck all :D

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5 weeks ago, # |
  Vote: I like it -18 Vote: I do not like it

Is this the first 11-problem CodeForces round in history?

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5 weeks ago, # |
  Vote: I like it 0 Vote: I do not like it

I was waiting for score distribution. Finally.

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5 weeks ago, # |
  Vote: I like it 0 Vote: I do not like it

jiangly 4000+?

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5 weeks ago, # |
  Vote: I like it 0 Vote: I do not like it

Hi, in the contest I submitted problem D and passed pretest but I wasn't really sure if my submission will pass sys test, and I change map to gp_hash_table and resubmited 2 times. To my suprise I got -100 points. Can anyone tell me why did I get -100 points and if my first submission get accepted will I get my 100 points back?

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    5 weeks ago, # ^ |
      Vote: I like it 0 Vote: I do not like it

    it was written above "Submit" button

    "Be careful: there is 50 points penalty for submission which fails the pretests or resubmission"

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      5 weeks ago, # ^ |
        Vote: I like it 0 Vote: I do not like it

      Damn i didn't see that, I used to resubmit in div 3 and thought div 2 was the same, thanks for the clarification.

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5 weeks ago, # |
← Rev. 2   Vote: I like it +5 Vote: I do not like it

Jiangly becomes a Tourist in the last minute!

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5 weeks ago, # |
  Vote: I like it 0 Vote: I do not like it

jiangly Is now Jiangly....

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5 weeks ago, # |
  Vote: I like it 0 Vote: I do not like it

jiangly 4000+ WOW

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5 weeks ago, # |
  Vote: I like it +11 Vote: I do not like it

Seems like jiangly 4K

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5 weeks ago, # |
  Vote: I like it -8 Vote: I do not like it

Jiangly clutch >>

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5 weeks ago, # |
← Rev. 3   Vote: I like it 0 Vote: I do not like it

Orzz!!!! jiangly is Goated... Highest ever codeforces rating incoming..

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

jiangly did it !!!!!

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5 weeks ago, # |
  Vote: I like it +19 Vote: I do not like it

Problem D: 1654C - Alice and the Cake

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

jiangly orzzz

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5 weeks ago, # |
  Vote: I like it +36 Vote: I do not like it

Thank you for the contest! The problems were really interesting. Best Codeforces round in a while.

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5 weeks ago, # |
  Vote: I like it +6 Vote: I do not like it

orz!!!! jiangly

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5 weeks ago, # |
  Vote: I like it +1 Vote: I do not like it

in the end battle was really between jiangly and tourist

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5 weeks ago, # |
  Vote: I like it 0 Vote: I do not like it

Incredible round. Can't wait to upsolve

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5 weeks ago, # |
  Vote: I like it +1 Vote: I do not like it

Jiangly's comeback is insane! Congratz

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5 weeks ago, # |
  Vote: I like it 0 Vote: I do not like it

How were we supposed to solve C.

i thought about it as dp previous and current of size n*2. previous[i][0] tells the number of ways when i number of liars and the current guy speaks truth. vice versa

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    5 weeks ago, # ^ |
      Vote: I like it 0 Vote: I do not like it

    First iterate over whole array and see that whenever arr[i] > i the person is telling lie. Because there are no enough people on his left side. Then apply dp.

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    5 weeks ago, # ^ |
      Vote: I like it 0 Vote: I do not like it

    3d DP. dp[currentIndex][prevNumberOfLiars][isPrevIdxHonest]

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    5 weeks ago, # ^ |
      Vote: I like it 0 Vote: I do not like it

    This might be the most cursed optimization I did for any dp problem.

    I found the dp to be this:

    Spoiler

    And then some steps later:

    Спойлер
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    5 weeks ago, # ^ |
      Vote: I like it +1 Vote: I do not like it

    2*n dp. If ith person is liar, then definitely i -1th person is honest. If ith person is honest, then two cases: i-1th person is liar (then i-2th person must be honest, and this also means that a[i] == a[i – 2] + 1 must be true), or i-1th person is honest (then a[i] == a[I – 1] must be true). Now make transitions accordingly. https://codeforces.net/contest/2061/submission/302092916

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5 weeks ago, # |
  Vote: I like it +3 Vote: I do not like it

best contst in recent times, felt very very good after competing

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5 weeks ago, # |
  Vote: I like it +19 Vote: I do not like it

speedforces

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

Could someone share some ideas for problem G? I think this problem is quite interesting, even though I couldn't figure out the solution during the contest.

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5 weeks ago, # |
  Vote: I like it +21 Vote: I do not like it

Problem C is cool

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5 weeks ago, # |
  Vote: I like it 0 Vote: I do not like it

Can anyone help me why I got WA. THanks so much in advance https://codeforces.net/contest/2061/submission/302128283

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5 weeks ago, # |
  Vote: I like it 0 Vote: I do not like it

why my brutefroces soultion doesen't work on E :(

302125235

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5 weeks ago, # |
  Vote: I like it +11 Vote: I do not like it

So many solutions got FST on B :/

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    5 weeks ago, # ^ |
      Vote: I like it +14 Vote: I do not like it

    I failed in a = {1,5,5,6}

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    5 weeks ago, # ^ |
      Vote: I like it 0 Vote: I do not like it

    I think I'm going back to newbie bc of this lol. I solved A after B, making this fatal.

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    5 weeks ago, # ^ |
      Vote: I like it +1 Vote: I do not like it

    For some reason, there was no pretest in case the bases of the hypotenuse lie on opposite sides of its equal edges (for example, the 11th system test 1 2 2 4).

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5 weeks ago, # |
  Vote: I like it +2 Vote: I do not like it

One of the best contests recently, I liked problem C but I think it's harder than D and F1 (I assume, still waiting for the system testing torture to be over to confirm whether my solution is correct or not)

But didn't like B much, had to search the entire internet to know what lengths can make an isosceles trapezoid...

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5 weeks ago, # |
  Vote: I like it +10 Vote: I do not like it

I swear I might just be getting dumber as more contests come and go...

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5 weeks ago, # |
  Vote: I like it +39 Vote: I do not like it

Any chance finals can be rescheduled to avoid conflict with both European and Asia Pacific ICPC Finals?

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5 weeks ago, # |
  Vote: I like it +30 Vote: I do not like it

B >>>>>>>>>>>>> F1

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5 weeks ago, # |
  Vote: I like it 0 Vote: I do not like it

In Problem B, my solution is O(nlogn), but it still gave TLE on system testing: Please help : https://codeforces.net/contest/2061/submission/302060527

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    5 weeks ago, # ^ |
      Vote: I like it +5 Vote: I do not like it

    I think multiset.count is not O(logN) but O(# elements to be counted)

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5 weeks ago, # |
  Vote: I like it -53 Vote: I do not like it

lesson learned:Never attend chinese round

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5 weeks ago, # |
  Vote: I like it 0 Vote: I do not like it

Congrats jiangly on becoming jiangly :)

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    5 weeks ago, # ^ |
      Vote: I like it 0 Vote: I do not like it

    But max is still showing tourist. May be they will fix it later.

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5 weeks ago, # |
  Vote: I like it +10 Vote: I do not like it

Interesting round!

Question about onsite: Is it right that it is okay to just participate in this round and then wait? I couldn't find any registration on the IAEPC website.

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5 weeks ago, # |
  Vote: I like it 0 Vote: I do not like it

Any idea why this code for B failed? I looked for everything but couldn't find the issue. Am i missing something? https://codeforces.net/contest/2061/submission/302078148

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    5 weeks ago, # ^ |
      Vote: I like it 0 Vote: I do not like it

    1 5 8 10 10 12 100

    look at this testcase

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    5 weeks ago, # ^ |
      Vote: I like it 0 Vote: I do not like it

    if(i-2>=0 && prefix[i-2]!=-1) should be replaced with if(i-2>=0 && prefix[i-2]!=-1 && arr[prefix[i-2]+1] - arr[prefix[i-2]] < 2*arr[i]), and else if(i+1<n && suffix[i+1]!=-1) with else if(i+1<n && suffix[i+1]!=-1 && arr[suffix[i+1]+1] - arr[suffix[i+1]] < 2*arr[i]). This way, even if the minimum differenve pair is not valid, you will still check the other options.

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      5 weeks ago, # ^ |
        Vote: I like it 0 Vote: I do not like it

      I just clocked it. Thanks a lot. gotta stop making such mistakes :(

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        5 weeks ago, # ^ |
          Vote: I like it 0 Vote: I do not like it

        Everyone makes such mistakes all the time. Don't worry, with practice you'll make them less often and get much better at spotting them.

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5 weeks ago, # |
  Vote: I like it +9 Vote: I do not like it

Thank you for the round! And could you please clarify what is included under 'travel expenses'? Does it cover round-trip flights, accommodation, meals, and other related costs?

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5 weeks ago, # |
  Vote: I like it 0 Vote: I do not like it

Congratulations!! jiangly, All eyes on jiangly ❤️

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5 weeks ago, # |
  Vote: I like it -38 Vote: I do not like it

why rating is not changing?

i have submitted A and accepted also

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5 weeks ago, # |
  Vote: I like it 0 Vote: I do not like it

what are sort?

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5 weeks ago, # |
  Vote: I like it 0 Vote: I do not like it

can anyone tell where this failed Problem -B? https://codeforces.net/contest/2061/submission/302086865

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5 weeks ago, # |
← Rev. 2   Vote: I like it +5 Vote: I do not like it

Just a quick information:

System testing for Codeforces Round 998 (Div. 3) is still running, so we need to wait for a little more before we can get rating update one by one.

Edit: lol, I guess we'll get a rollback to apply it later.

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5 weeks ago, # |
  Vote: I like it +21 Vote: I do not like it

Screencast of me solving this contest in Rust. No camera as it was blocked by some app

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5 weeks ago, # |
  Vote: I like it 0 Vote: I do not like it

My solution shows pretest passed after the system testing has ended. It neither shows wrong answer nor accepted. Why is this issue happening?

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

Finally jiangly has surpassed tourist. Congrats

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5 weeks ago, # |
  Vote: I like it 0 Vote: I do not like it

Auto comment: topic has been updated by jqdai0815 (previous revision, new revision, compare).

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5 weeks ago, # |
  Vote: I like it 0 Vote: I do not like it

Auto comment: topic has been updated by jqdai0815 (previous revision, new revision, compare).

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5 weeks ago, # |
  Vote: I like it 0 Vote: I do not like it

If v[0] = 0 isn’t it obvious that he is telling truth as nobody on the left?

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    5 weeks ago, # ^ |
      Vote: I like it 0 Vote: I do not like it

    You have to count number of ways, so You can also assume that he is telling lie

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5 weeks ago, # |
← Rev. 2   Vote: I like it +20 Vote: I do not like it

Thanks for the very nice round!

When trying to solve H2, I realized that my solution for H1 fails on this testcase:

1
4 2
1001
1010
1 2
3 4

Essentially, I was processing the connected components completely independently.

I was not sure if I should resubmit, as we often have pretests equal to systests these days. However, I convinced myself that there should definitely be a case in systests that verifies something that every reference solution needs to have an if for, and resubmitted. It turns out pretests were equal to systests in this problem as well :)

(It seems that all solutions of the top participants on the scoreboard handle this correctly, only 1 out of 12 accepted submissions fails this case)

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5 weeks ago, # |
  Vote: I like it 0 Vote: I do not like it

Auto comment: topic has been updated by jqdai0815 (previous revision, new revision, compare).

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

Untitled-Export-V4

Tourist -> <-

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5 weeks ago, # |
  Vote: I like it +3 Vote: I do not like it

How did this round's rating come before the previous round? Won't it require recalculation once the last round is done?

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5 weeks ago, # |
  Vote: I like it +15 Vote: I do not like it

Congratulations jiangly for crossing 4000 rating.

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5 weeks ago, # |
  Vote: I like it +3 Vote: I do not like it

wtf jiangly became Tourist ?

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5 weeks ago, # |
  Vote: I like it 0 Vote: I do not like it

"In C, I saw a recursive DP solution where cnt (the number of liars up to i) was passed as an argument. However, cnt was not used as a state in the DP table. Why is this? There can be multiple possibilities for a particular dp[i][prev]. Could someone explain?"

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ int dp[200001][2]; int n; vectorv; int ok(int i , int prev , int cnt){ if(i == n){ return 1; } int ans = 0; if(dp[i][prev] != -1 ){ return dp[i][prev]; } if(v[i] == cnt){
ans = (ans+ok(i+1,0,cnt))%MOD; } if(prev == 0){ ans = (ans + ok(i+1,1,cnt+1))%MOD ; } dp[i][prev] = ans; return ans;

} void solve(){ cin >> n; v.resize(n); loop(i,n,1){ cin >> v[i]; }
memset(dp,-1,sizeof(dp));
int ans = ok(0,0,0); cout << ans << "\n";

} ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

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5 weeks ago, # |
  Vote: I like it -16 Vote: I do not like it

Thanks for the round. It had some nice problems, especially D and G (and to some extent F1) among the ones i solved anyways.

On the other hand, BC werent that great (but thankfully didnt ruin my experience). I think easy problems like D with a simple observation are preferable to yet another "code a casework dp"

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

nvm

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5 weeks ago, # |
  Vote: I like it 0 Vote: I do not like it

can someone plz help in finding the counter test case of my submission for Problem B

It fails on test file 18, test case 149.

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5 weeks ago, # |
  Vote: I like it +1 Vote: I do not like it

Congratulations to jiangly for achieving the highest-ever rating on Codeforces!

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5 weeks ago, # |
  Vote: I like it +68 Vote: I do not like it

Another fun experience in this contest was that when I looked at problem H2, it had this notification at the top: "The problem statement has recently been changed. View the changes."

And when I clicked on "View the changes", it showed me that the sample output has changed, even with a nice diff:

Since there was no announcement, my theory is that this was an accidental leak of the reference solution output. What the reference solution seems to do is to just keep moving there and back in the beginning and at the end (probably using the matchings we find in H1), and then each token at some point just moves without stopping from the starting to the ending location. Still not sure how to complete this to a working solution, though :)

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    3 weeks ago, # ^ |
      Vote: I like it -10 Vote: I do not like it

    Hmm, I think this is not the leak of MCS output. The authors intentionally changed the output at the last minute before the contest.

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5 weeks ago, # |
  Vote: I like it +23 Vote: I do not like it

I loved problem D!

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5 weeks ago, # |
  Vote: I like it +4 Vote: I do not like it

Why the Hell is Jiangly given the rank of "Tourist"? It should be that, anyone who crosses 4000 must have the rank same as their handle. Also, heartiest Congrats to Jiangly for making it.

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5 weeks ago, # |
  Vote: I like it +20 Vote: I do not like it

Problem G, I — amazing! Other problems were great too, I liked everything except A. Thanks for an awesome round!

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5 weeks ago, # |
← Rev. 2   Vote: I like it +3 Vote: I do not like it

All the div1+2 giving me negative deltas... But I feel this contest was really good, actually worth it anyway. Upsolved both C and D.

Thanks for the great contest.

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5 weeks ago, # |
← Rev. 6   Vote: I like it 0 Vote: I do not like it

Can someone please help me finding what is wrong with my submission 302299299 in problem E div2. I tried for hours to catch the problem, but I could not, then I read the tutorial and recognized that my solution is similar (maybe I am wrong in this). Is the code wrong or the idea is wrong?

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4 weeks ago, # |
  Vote: I like it 0 Vote: I do not like it

If everyone who scores over 4000 can get their username as a level name, it would be cool

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4 weeks ago, # |
  Vote: I like it 0 Vote: I do not like it

hii Codeforces, please check them out Lakshya29J for problem D of this round, his solution matches from one of the solution posted in the a video in youtube.

also checkout Aryan_0718 for both problem C and Problem D, these solutions exactly matches the one made public on Youtube and these solutions also matches.

I found many users submitting the exact same solutions and then saw the exact same solutions on Youtube.

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4 weeks ago, # |
  Vote: I like it 0 Vote: I do not like it

what are the game?

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11 days ago, # |
  Vote: I like it +1 Vote: I do not like it

I have question ,why my rating was reset

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