18o3's blog

Indian ICPC 2022-23 Regionals — Qualifier Rounds
By 18o3, history, 3 days ago, In English

This year there will be two separate online qualifier rounds for the two regionals.

The contest for Mathura is from 2pm to 4pm IST on 18th March 2023. Link
The contest for Amritapuri site is from 8pm to 10pm IST on 18th March 2023. Link

Let's use this blog to discuss the rounds after they end.

Hope to see you all on the leaderboard.

 
 
 
 
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3 days ago, # |
  Vote: I like it +17 Vote: I do not like it

Best of Luck everyone!

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3 days ago, # |
  Vote: I like it +141 Vote: I do not like it

Kanpur Mathura prelims has to be the worst ICPC contest, probably ever. Imagine setting 4 problems for a team of 3, and so easy that all of them could easily be solved in $$$\lt$$$ 20 minutes total. And then to add icing on the cake the penalty for a single wrong submission is 20 minutes as well

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3 days ago, # |
  Vote: I like it +42 Vote: I do not like it

This is just sad. Wait, no, not just sad. Sad and enraging. Great job!

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3 days ago, # |
  Vote: I like it +53 Vote: I do not like it

Was this ICPC qualifier or leetcode contest? 0_0

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    3 days ago, # ^ |
      Vote: I like it +73 Vote: I do not like it

    No, leetcode contests are harder.

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    3 days ago, # ^ |
      Vote: I like it +54 Vote: I do not like it

    Enough with the direspect bro, this can’t be accepted,

    leetcode contests are much better than this

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3 days ago, # |
  Vote: I like it +33 Vote: I do not like it

speedforces

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3 days ago, # |
  Vote: I like it 0 Vote: I do not like it

Can anybody tell why this got TLE?

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3 days ago, # |
  Vote: I like it +111 Vote: I do not like it

If you take 10 lakh rupees as cumulative fees for just the prelims, it is just downright shameful coming up with such a problemset. Probably should reassess whether your priority is advancement of CP or just a pitiful money grab

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3 days ago, # |
  Vote: I like it +93 Vote: I do not like it

Refund.

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

Can someone please tell me why this got TLE ?

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    3 days ago, # ^ |
      Vote: I like it +6 Vote: I do not like it

    You can't rely on 2d-vectors where your complexity is $$$\mathcal{O}(N^2 \cdot T)$$$ which is probably $$$8 \cdot 10^8$$$ iterations, with time limit of 3s.

    Use 2d-arrays instead.

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3 days ago, # |
  Vote: I like it +58 Vote: I do not like it

How to make a 1600 rated problem 1800.

Give input in floating points.

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    3 days ago, # ^ |
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    More like 1200 into 1400 but yeah, that was so annoying (:

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3 days ago, # |
  Vote: I like it +14 Vote: I do not like it

Speedforces af.

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3 days ago, # |
  Vote: I like it +8 Vote: I do not like it

worst contest I have seen

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3 days ago, # |
← Rev. 2   Vote: I like it +23 Vote: I do not like it

Preparing for ICPC prelims:

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3 days ago, # |
  Vote: I like it -11 Vote: I do not like it

Can anyone give a testcase that fails this code for B? Cannot understand what is wrong with this approach.

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    3 days ago, # ^ |
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    What when s[i] is equal to value at both pointers!

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    3 days ago, # ^ |
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    I used the same approch but sill not able to understand why equal value would effect

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

What happened to that tradition of ICPC where one problem is solved by all teams and one problem is not solved by any team Why having prelims as div 69420 contest

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3 days ago, # |
  Vote: I like it +14 Vote: I do not like it

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

How many teams will be selected from each institute ?

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

Kanpur regionals qualification rules have been updated here

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    3 days ago, # ^ |
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    do you have the same for Amritapuri regionals?

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3 days ago, # |
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Does anyone know how many slots are there for Mathura Regionals?

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3 days ago, # |
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The quantity of questions was less. More sort of data structure problems.

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3 days ago, # |
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Friendly remainder: s=s+b not equal to s+=b

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3 days ago, # |
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Why is nlogn solution giving TLE for XOR sort?

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    3 days ago, # ^ |
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    For me it didn't

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      3 days ago, # ^ |
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      This gave TLE

      Spoiler
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        3 days ago, # ^ |
          Vote: I like it +28 Vote: I do not like it

        #define endl "\n"
        195 ms

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          3 days ago, # ^ |
            Vote: I like it +53 Vote: I do not like it

          I’m jumping off the terrace

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

            after 1st tle even optimized it to o(n), still didn't make it. Our team is jumping off too.

            code
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3 days ago, # |
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How to solve central subset?

link

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    3 days ago, # ^ |
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    Centroid decomposition ig

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    3 days ago, # ^ |
    ← Rev. 2   Vote: I like it +23 Vote: I do not like it

    Let sz(x) mean the size of the subtree rooted at x. Formally $$$sz(x) = 1 + \sum sz(v)$$$ for all children $$$v$$$ of $$$x$$$.

    Choose an arbitrary root and walk through the tree normally with a dfs calculating values of $$$sz$$$. For any node where $$$sz(x) \geq \sqrt{n}$$$, add $$$x$$$ to the subset and consider $$$sz(x) = 0$$$ for further calculations.

    Why does this work?

    • For any child $$$v$$$ of $$$x$$$, $$$sz(v) \lt \sqrt{n}$$$, so the distance between any node in this subtree from $$$v$$$ must also be $$$\lt \sqrt{n}$$$. Since $$$v$$$ is a child of $$$x$$$, the distance of any node in the subtree from $$$x$$$ is $$$\lt \sqrt{n} + 1$$$ or in other words $$$\leq \sqrt{n}$$$.

    • Since $$$sz(x) \geq \sqrt{n}$$$ whenever we perform this, we add at most $$$\frac{n}{\sqrt{n}} = \sqrt{n}$$$ nodes to the subset.

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

    1) Pick any spanning tree and root at node $$$1$$$.

    2) Pick the node having the max depth, go up $$$\sqrt{n}$$$ for that node following parents, push this one in the answer, and remove that subtree.

    3) Do step 2 until the tree is not empty.

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3 days ago, # |
← Rev. 2   Vote: I like it +42 Vote: I do not like it

Kudos to Amritapuri online round setters, it felt like a fairly nice and balanced round (except for maybe a bit of an aggressive difficulty jump after the first problem). I really liked how cute the solution to problem A is.

Not at all biased by rank 11 in Amritapuri qualifier vs rank 227 in Mathura qualifier :P

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    3 days ago, # ^ |
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    Yeah Amritapuri was relatively better, getting a lower rank didn't hurt in Amritapuri but it did in Mathura ;(

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

What are the qualification rules for amritapuri?

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3 days ago, # |
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Did anyone manage to get non-TLE with $$$n \sqrt{n}$$$ on A?

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    3 days ago, # ^ |
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    Ya I guess my worst case would be n^(3/2), you can refer here

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3 days ago, # |
  Vote: I like it +4 Vote: I do not like it

Will there be additional system testing on the Amritapuri prelims?

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3 days ago, # |
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How many seats are there for kanpur-mathura regionals?

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3 days ago, # |
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For the mathematicians and physicists problem of amritapuri region we did dp ( very similar to this problem), but got mle even after replacing 2 d input array by a map of pairs.Any suggestions?

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3 days ago, # |
← Rev. 3   Vote: I like it -28 Vote: I do not like it

Thank you.

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3 days ago, # |
  Vote: I like it +13 Vote: I do not like it

How to solve The number of good subarrays

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    3 days ago, # ^ |
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    For each L you can find the smallest R by binary search and if L,R is good then L,(R+1) is also good.

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      3 days ago, # ^ |
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      Could you please elaborate your checker function of binary search

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        3 days ago, # ^ |
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        So for checking if a subarray is good after removing [l,r] you need to count the f(rem) array, for that you can take the contribution of each bit for example if ith bit is set in k subarrays then the contribution will be 2^i*k for finding the number of subarray that has ith bit set you can do is total_subarray-number_of_subarrays_where_ith_bit_is_off. For achieving this you can keep some prefix suffix arrays.

        Refer this code for solution: here

        PS: Sorry for my alien language :(

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

Kanpur-Mathura Online Qualifier Round unofficial list here. (made by me :))

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    2 days ago, # ^ |
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    What are the numbers next to the college name? The number of teams qualifying?

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      2 days ago, # ^ |
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      Nope, they're just the count, stating the no of times that college is present in under 100.

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    46 hours ago, # ^ |
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    is the selection criteria for kanpur-mathura regionals same as amritapuri regionals? Like do they too 1st select the top team from every other colleges?

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    18 hours ago, # ^ |
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    Our team has rank 45 from Kanpur-Mathura and we are the 2nd team from our college and the 1st team has rank 10 so do we stand a chance for regionals

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      18 hours ago, # ^ |
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      Yes, ofc!

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        13 hours ago, # ^ |
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        If one team is selected from a college, 2nd team wouldn't be allowed, right ?

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          13 hours ago, # ^ |
            Vote: I like it +4 Vote: I do not like it

          That is the rule for Amritapuri regionals, not Mathura regionals. You can check last year's criteria here.

          I can't believe that such a great singer is on Codeforces. I am your big fan.

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2 days ago, # |
  Vote: I like it +15 Vote: I do not like it

Are qualification rules for Amritapuri same as last year? Can more than 3 teams qualify from an institute?

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18 hours ago, # |
  Vote: I like it +27 Vote: I do not like it

Any ideas as to when the results would be announced? As the regional dates are close approaching, and most of us would need to book flights to get to Bangalore/Amritapuri.

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