IceKnight1093's blog

Invitation to CodeChef July Lunchtime (Rated for all) — 17th July 2022
By IceKnight1093, 2 years ago, In English

We invite you to participate in CodeChef’s July Lunchtime, this Sunday, 17th July, rated for all.

Time: 8:00 PM — 11:30 PM IST

Please note, the contest duration is changed to 3.5 Hours, i.e, from 8:00 PM — 11:30 PM

Joining me on the problem setting panel are:

The video editorials of the problems will be available on our YouTube channel as soon as the contest ends. Subscribe to get notifications about our new editorials.

Also, if you have some original and engaging problem ideas, and you’re interested in them being used in CodeChef's contests, you can share them here.

Since this contest contains problems from the Indian IOI Team Selection Tests, those students are requested to not participate.

Hope to see you participating. Good Luck!

  • Vote: I like it
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Comments Comments (24)
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2 years ago, # |
  Vote: I like it +8 Vote: I do not like it

3.5 hours for how many questions?

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    2 years ago, # ^ |
      Vote: I like it +34 Vote: I do not like it

    There are 6 in Div1, 7 in Div2 and Div3, and 8 in Div4.

    Many of the later problems have several subtasks, so you are encouraged to read every problem.

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

Ig its july lunchtime not june's lunchtime.

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

https://www.codechef.com/viewsolution/69250616 how is this solution wrong for 13 point Tree Retrieval

and https://www.codechef.com/viewsolution/69257276 this for 4 point Inversions Retrieval

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

    I think you forgot to take the input where the judge tells you whether your answer for that test is right or wrong .

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      2 years ago, # ^ |
        Vote: I like it +31 Vote: I do not like it

      i feel i wasted 3.5 hrs of my life torturing myself

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    2 years ago, # ^ |
    ← Rev. 3   Vote: I like it +13 Vote: I do not like it

    For 13-point Tree Retrieval, you should take input 1 or -1 after printing the edges. I had missed it too :XD
    And for 4-point Inversions Retrieval, you missed to print the number of operations you are doing in the starting.

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

      thanks, i think i need a break. But how did 4-point inversions retrieval pass 2 test

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

Great problems! Found Div 1 quite hard though, and with so many subtasks it felt almost like a long challenge xD

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2 years ago, # |
  Vote: I like it +18 Vote: I do not like it

How to judge INVRET? Randomizing scheme?

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

Brief Solution for INVRET:

Subtask 1
Subtask 2
Subtask 3
Subtask 4,5
Subtask 6,7,8
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    2 years ago, # ^ |
      Vote: I like it +16 Vote: I do not like it

    This was genuinely one of the best problems I have ever seen. orz work

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    2 years ago, # ^ |
    ← Rev. 2   Vote: I like it +49 Vote: I do not like it

    Congrats to kshitij_sodani who could solve it during the Indian IOI TST, and ritul_kr_singh who almost solved it too.

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

    I got $$$924099$$$ queries. You can see the code here. Also with $$$N=7500$$$, I only use $$$999597$$$ queries.

    In the solution, you have to calculate the number of inversions of a binary string. I believe the intended solution does this in $$$3n$$$ queries. However, I can do it in $$$2n + 8 \frac{n}{k}$$$ queries with additional $$$2 \cdot 2^k$$$ queries in the beginning. I used $$$k=12$$$ in the above solution. We split the binary string into chunks of $$$k$$$ bits. If we precomputed a lookup table for the number of inversions and their popcount, it is easy (albeit super tedious) to handle the contribution of appending a binary string of size $$$k$$$.

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

The problems seemed nice (even though I statpatted on subtasks)
Anyways, were all the problems used for IOI TST? And speaking of problems, can we find the previous years' problems anywhere?

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

Deleted

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

Yesterday during the contest, I submitted the solution for Tree Interval Queries (TREEQUER) which got partially accepted for 10 points. In the rank list under problem section points for that part has been given but it was not added to my total score and therefore my rank was also not updated. I don't know why it happened, can anyone clarify that? I would be thankful if something would be done to rectify that. Thanks in advance. Here's the link to My Solution

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

    Thanks for reporting. It should be fixed now.

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

      Thanks a lot for looking into this so quickly and rectifying it. Thanks a lot once again :)

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