chokudai's blog

By chokudai, history, 2 months ago, In English

We will hold AtCoder Beginner Contest 212.

The point values will be 100-200-300-400-500-500-600-600.

We are looking forward to your participation!

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

Why downvote this blog? It will be a nice contest!

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    2 months ago, # ^ |
    Rev. 3   Vote: I like it +41 Vote: I do not like it

    I think the reason being is:

    5:30 — 7:10 PM IST: AtCoder Beginner Contest 212

    6:00 — 8:30 PM IST: ICPC Amritapuri 2020 Mock Round (For Indians)

    6:00 — 9:00 PM IST: July 2021 CodeChef Lunchtime (With Extra Prizes for Indians)

    Collision at the peak :)

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      2 months ago, # ^ |
        Vote: I like it +24 Vote: I do not like it

      Simple choice for me.Because I love AtCoder more than any problem solving website

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        2 months ago, # ^ |
          Vote: I like it -21 Vote: I do not like it

        For Indians, the simple choice would be ICPC mock since ICPC >>>> any problem solving website :)

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

New rule of ABC : 8 Tasks 100 minutes It will take speedsolving to another level

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2 months ago, # |
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Unusual score distribution

Spoiler

It must be a nice contest!

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2 months ago, # |
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Clash with CodeChef Lunchtime!

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2 months ago, # |
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8 problems, still burned all remaining time on O(n^gajillion) approach to E.

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

How to solve E?

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

    just do the following K times: suppose dp[i] is the number of paths that end at i, initially only dp[1] = 1.

    For every day, all vertices can go to i except those that are broken(and i, of course). So you can just do $$$nextdp[i] = \sum dp[i] - \sum _{j \in adj[i]} dp[j] - dp[i]$$$ , then just swap nextdp and dp.

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

      I thought it would be TLE . Is not TLE only because size of all adj[i] won't be 5000 ?

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

I used Fast Walsh for H. Is it needed?

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2 months ago, # |
  Vote: I like it +24 Vote: I do not like it

tourist is too fast.

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    2 months ago, # ^ |
      Vote: I like it +39 Vote: I do not like it

    Well this was the only choice he has! Since he has to top the Codechef Lunchtime also and He manage to get 2 min break in between.

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

D was nice, even though I couldn't pass all test cases

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

E was a great problem, thank you for teaching me dp on trees ( atleast a part of it ).

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

    Can anyone tell me the reason for downvote? Was it not "dp on trees" or is something else the reason for downvote?

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

      I doubt it has a flavor of "DP on tree," but still I don't see any reason on downvoting it... (Some of them may be downvoting you just because you're gray, which attitude I don't like)

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

        Yes I realised it later.....the graph might not even be a tree so dp on trees is wrong...thank you.

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2 months ago, # |
  Vote: I like it +24 Vote: I do not like it

I feel like implementing F was way harder than G.

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2 months ago, # |
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I am not able to understand the editorial of E. Can somebody explain it or refer to some other resource for it?

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2 months ago, # |
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Code

Can someone explain why my code got tle for E

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    2 months ago, # ^ |
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    The issue with your code is that in worst case, it runs in approximately $$$O(n^2k)$$$ because there could be maximum $$${n(n-1)/2} - m$$$ valid edges, so for each iteration of $$$i$$$, the inner loop runs in $$$O(n^2)$$$, hence the TLE.

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

    You should use adjacency list instead of adjacency matrix for checking the banned ways, improving from $$$n^2$$$ to $$$n + 2*m$$$ for the inner loop when reducing the banned ways

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2 months ago, # |
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Thank You for the wonderful problemset. The number of tasks was a little too much considering only 100 mins to solve them.

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2 months ago, # |
  Vote: I like it +20 Vote: I do not like it

As a writer of ABC(sadly this time I'm not), I'm curious about how do participants feel with the new format.

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    2 months ago, # ^ |
      Vote: I like it +25 Vote: I do not like it

    i wish there was infinity of such genuine,geniosity,pure beauty,attractive,elegant,gorgeous,inspiring,exciting... problems :) thank you .

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    2 months ago, # ^ |
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    So you are saying this was not a one time thing ?

    Anyways, if the 8 problem ABC is going to be adapted for further ABC too. I wish these 2 points to be implemented.

    1. Increase duration a bit (maybe like make it 2 hours ? )
    2. Make problem >= F, more in the reach of actual rated range participants. For me personally today, I was done till E in 25 mins and then I stared at screen for rest whole contest. But yes, I understand its my fault and F was actually not that out of reach, but still I think it was pretty hard. (That can be seen by yellow rating to F, G and orange rating to H at kenkoo)
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    2 months ago, # ^ |
      Vote: I like it +3 Vote: I do not like it

    Is this going to be the new standard format? If so, sounds fun!

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2 months ago, # |
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Hii, I tried to solve D via method 1, and then method 2, I failed to see why first one didn't work, could u help me out please.

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    2 months ago, # ^ |
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    Try the following trivial testcase with your incorrect code and you should easily see what's wrong with it, the correct output is 2 11:

    Testcase
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2 months ago, # |
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x^n≡y(mod P) ⇔r^an≡r^b(mod P) ⇔an≡b(mod P−1) How is the second step to the third step transformed? Who can explain? Thank you very much

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    2 months ago, # ^ |
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    this problem is G

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      2 months ago, # ^ |
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      Because for every i(1<=i<=P-1),r^i is distinct ,so we can know for every r^i there is exactly one such i.

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7 weeks ago, # |
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I think problem E could be solved by using kitamasa method. Anyone have AC code?