18o3's blog

By 18o3, history, 12 months 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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12 months ago, # |
  Vote: I like it +17 Vote: I do not like it

Best of Luck everyone!

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12 months 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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12 months 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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    12 months ago, # ^ |
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    No, leetcode contests are harder.

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    12 months ago, # ^ |
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    Enough with the direspect bro, this can’t be accepted,

    leetcode contests are much better than this

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12 months ago, # |
  Vote: I like it +33 Vote: I do not like it

speedforces

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12 months ago, # |
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Can anybody tell why this got TLE?

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12 months 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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12 months ago, # |
  Vote: I like it +93 Vote: I do not like it

Refund.

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12 months 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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    12 months 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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      12 months ago, # ^ |
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      Thanks a lot!

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      12 months ago, # ^ |
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      I'm about to cry

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        12 months ago, # ^ |
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        Already did :) Four TLE's because of this lol.

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        12 months ago, # ^ |
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        idk why, my solution got accepted , i have used 2-D vectors too.

        Any idea how many slots are there in kanpur-mathura? I hope there should be 120 seats :/

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          12 months ago, # ^ |
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          Lucky you :')

          As always, no official info. from them. But if we see last year, Kanpur had 70 seats, so Kanpur + Mathura should be around 120 to 140. Just a guess though.

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12 months 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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    12 months ago, # ^ |
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    More like 1200 into 1400 but yeah, that was so annoying (:

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12 months ago, # |
  Vote: I like it +14 Vote: I do not like it

Speedforces af.

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12 months ago, # |
  Vote: I like it +8 Vote: I do not like it

worst contest I have seen

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12 months ago, # |
Rev. 2   Vote: I like it +23 Vote: I do not like it

Preparing for ICPC prelims:

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12 months 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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    12 months ago, # ^ |
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    What when s[i] is equal to value at both pointers!

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    12 months 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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12 months ago, # |
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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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12 months ago, # |
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12 months ago, # |
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How many teams will be selected from each institute ?

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12 months ago, # |
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Kanpur regionals qualification rules have been updated here

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    12 months ago, # ^ |
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    do you have the same for Amritapuri regionals?

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

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12 months ago, # |
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Why is nlogn solution giving TLE for XOR sort?

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    12 months ago, # ^ |
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    For me it didn't

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      12 months ago, # ^ |
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      This gave TLE

      Spoiler
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        12 months ago, # ^ |
          Vote: I like it +28 Vote: I do not like it

        #define endl "\n"
        195 ms

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          12 months ago, # ^ |
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          I’m jumping off the terrace

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            12 months ago, # ^ |
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            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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12 months ago, # |
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How to solve central subset?

link

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    12 months ago, # ^ |
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    Centroid decomposition ig

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    12 months 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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    12 months 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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12 months ago, # |
Rev. 2   Vote: I like it +43 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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    12 months 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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12 months ago, # |
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What are the qualification rules for amritapuri?

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

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12 months 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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12 months ago, # |
Rev. 4   Vote: I like it +8 Vote: I do not like it

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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12 months ago, # |
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    12 months 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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      12 months ago, # ^ |
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      Could you please elaborate your checker function of binary search

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        12 months 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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12 months 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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    12 months ago, # ^ |
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    What are the numbers next to the college name? The number of teams qualifying?

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      12 months 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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    12 months 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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      12 months ago, # ^ |
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      Yes, ofc!

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

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          12 months ago, # ^ |
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          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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12 months ago, # |
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Are qualification rules for Amritapuri same as last year? Can more than 3 teams qualify from an institute?

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

gwalior pune region info anyone

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12 months ago, # |
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When will mathura region results gonna be declare?

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    12 months ago, # ^ |
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    today or tomorrow, there are 150 seats

    Source — codedrills telegram channel

    (someone claimed to got reply from icpc mathura-kanpur via email )

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      12 months ago, # ^ |
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      The guy who said on telegram : "Source: Trust me bro"

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      12 months ago, # ^ |
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      150 seats, r u serious?? Haha, According to Kanpur max to max 70-80 seats.

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        12 months ago, # ^ |
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        Yeah the seats in kanpur will be 70-80 but the combined seats of kanpur mathura should be atleast 130

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          12 months ago, # ^ |
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          It's not a combined regional site. It's only Mathura where the regionals are going to be held as per my knowledge.

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            12 months ago, # ^ |
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            Actually it's clearly mentioned on the icpc kanpur-mathura page that the contest is jointly hosted by GLA University,Mathura and CSJM University,Kanpur.

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              12 months ago, # ^ |
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              Ohh! Thank you for the info.

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12 months ago, # |
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12 months ago, # |
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can someone share official telegram link for mathura regionals?