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antontrygubO_o's blog

Invitation to CodeChef September Lunchtime (Rated for all) (Based on EJOI) — 23rd Sept
By antontrygubO_o, 2 years ago, In English

We invite you to participate in CodeChef’s September Lunchtime, this Friday , 23rd September, rated for all. It is based on EJOI 2022, the second day of which takes place earlier on the same day. All EJOI participants were asked to not discuss the problems before the end of this contest, and to not participate in this contest. If you somehow got to know some of the problems, please, don't participate.

Time: 8:00 PM — 11:30 PM IST

Please note that the contest duration is unusual — 3.5 Hours.

Joining me on the problem setting panel are:

The video editorials of the problems will be available for all users for 1 day as soon as the contest ends, after which they will be available only to Pro users.

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.

Hope to see you participating. Good Luck!

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Comments Comments (20)
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2 years ago, # |
  Vote: I like it -11 Vote: I do not like it

Can U Just Postpone the Contest to Day After Tomorrow or to Sunday .So me and every other person can join the LunchTime Contest After So Many Days .Since CodeForces Div 2 822 is Clashing with it

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

    Codeforces contest has been rescheduled. Check announcement!

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

Reminder: Contest starts in ~30 minutes.

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

How to solve RMVNUMBERS?

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

    If m >= 40 answer is 0. Otherwise you can calculate for each number in A, what mask of operations would leave it untouched. You can do dp on trie on those masks to calculate answer.

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

    If $$$M > 30$$$ the answer is $$$0$$$, otherwise we can brute-force on the game tree. See the code.

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

Got my best rank (34) in div2. feeling much better after rating loss in CF.. thanks for the contest :)

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2 years ago, # |
  Vote: I like it +36 Vote: I do not like it

RMVNUMBERS is a mastapiece!

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

how to solve Increasing Addition?

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

    Consider what the operation does to the difference array.

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

      max adjecent diff when a[i]>a[i+1]

      becouse in one operation 1,2,3.... add in every l to r element

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

        we want min(A[i]-A[i-1]) >= 0. So ans is -min(A[i]-A[i-1]) if min(A[i]-A[i-1]) < 0 otherwise its 0. We can use a multiset or map to store sorted adjacent difference.

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

      Lets say the Increasing Addition question was phrased as this: find Max ceil((a[i]-a[j])/(j-i))) among all pairs (i,j) where j>i.And there are q queries where you modify one element in each query.

      How would you approach this question?

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

Free 17pts was here(PERMSLCS Subtask3): ARC091-E

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

How to optimize LCAINTERACT from 66 points (k=10) to 100 points (k=9)?

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

How to solve UNFRIENDLY for the entire 100 points ? I could come up with only a dp solution for 23 points :( .

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

    Collapse substrings like "aaaaaaaa" into just "a" as you can't pick more than 1 from these anyway. Collapse substrings like "abababababababa" into just "aba", this won't affect the answer for a similar reason.

    Now you can show that it is never optimal to leave gaps longer than 2 in the subsequence. Now you can solve with a $$$O(n)$$$ DP.

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

I'm really impressed by the quality of codechef problems! I enjoyed Div 1 problems so much (even more than a typical Codeforces round!) Keep it up!

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