By PikMike, history, 2 weeks ago, translation, In English,

Hello Codeforces!

On April 15, 17:35 MSK will be held Educational Codeforces Round 19.

This Educational Round is held as Harbour.Space university initiative. It's the second round supported by Harbour.Space. You can read the details about the cooperation between Harbour.Space and Codeforces in the blog post.

Some educational programs in Harbour.Space are interesting for most Codeforces users. One of them is Data Science Program. Here is few words from Sergey Nikolenko, Harbour.Space lecturer and Senior Researcher, Steklov Institute of Mathematics at St. Petersburg Russia.

The round will be unrated for all users and it will be held with extented ACM ICPC rules. After that you will have one day to hack any solution you want. You will have access to copy any solution and test it locally.

You will be given 6 problems and 2 hours to solve them. We tried to prepare such problems that both novices and experienced coders will find something interesting in this contest.

The round was prepared by Ivan BledDest Androsov, Mikhail MikeMirzayanov Mirzayanov and me.

Wish you enjoy the contest! Good luck!

UPD: Editorial

 
 
 
 
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13 days ago, # |
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It overlaps with GoogleCodeJam round 1A !

UPD: It doesn't overlap .. thanks for yinanzhu and KieranHorgan

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13 days ago, # |
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is it rated?

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13 days ago, # |
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Why not all the contests have clear problem statements like this one. Thank you for this interesting contest.

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13 days ago, # |
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How to solve F?

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    12 days ago, # ^ |
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    I don't know the time complex of the std. But the time limit makes me think that the std have the time complex of O(n2).

    My solution's time complex is , and it costs 858ms.

    First it's easy to come up with the DP of O(n3). Then let's look at the programme carefully, and we can find out that it's very similar to Knapsack problem. And this classic problem have a classic way(divide each original item into items) to optimize it to

    We can use the same way to opimize the original problem. Then we solve the origine problem in

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13 days ago, # |
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very interesting problem set. I hope to see more problem set like this! :D

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13 days ago, # |
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Can anyone tell me why im getting TLE on E. My idea is precompute for every k below 1000 in O(N) each and just simulate all k bigger than 1000 (worst case scenario is 100 operations if im correct) 26393091

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13 days ago, # |
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Did someone pass TL42 with mincost maxflow on F?

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12 days ago, # |
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Never thought I could make more points than some reds or oranges. Strange contest =)

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12 days ago, # |
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How to solve C ????

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    12 days ago, # ^ |
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    You can solve it greedily.

    for (char c = 'a'; c <= 'z'; c++)
    {
      // Try to place current character 'c' in the target string.
    }
    
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      12 days ago, # ^ |
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      I am so dumb :( ....I really do not know anything :(

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        12 days ago, # ^ |
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        How did you manage to solve A and B if you consider yourself as dumb? :)

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      9 days ago, # ^ |
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      What special about test case 17? could not pass case 17 after multiple tries. my solutions:- 26491308 , 26469800

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        9 days ago, # ^ |
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        got the case where it is failing input :- abcfefg output :- abceffg

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12 days ago, # |
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Can someone explain to me why in the second test for E the 8th number is 2?

10
3 5 4 3 7 10 6 7 2 3
10
4 5
2 10
4 6
9 9
9 2
5 1
6 4
1 1 <-
5 6
6 4

p = 1, a[1] = 3, k = 1, n = 10;
Initially p = 1. After first operation p = 1 + 3 + 1 = 5. After second operation p = 5 + 3 + 1 = 9 < 10. What am I missing?

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    12 days ago, # ^ |
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    In the first operation p = 1 p = p + a[p] + k p = 1 + 3 + 1 p = 5 In the second operation p = 5 p = 5 + 7 + 1 p = 13 p > 10

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      12 days ago, # ^ |
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      Ah, I see. Thanks! I completely missed the fact that when p changes the array element chages as well.

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12 days ago, # |
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Please discuss the approach for problem F.

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    12 days ago, # ^ |
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    You can solve it using dynamic programming. Let DP[j][i] denote the minimum cost to assign the first i mice to the first j holes. For each state, iterate over the leftmost mouse you will assign the jth hole to. This takes O(m*n*n) time.

    But notice that for a fixed j, the optimal left-point is non-decreasing for non-decreasing i, i.e. optima[j][i] <= optima[j][i+1]. So you can speed up the DP using divide-and-conquer optimisation.

    Code

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      10 days ago, # ^ |
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      How do you deal with hole capacities and the fact that contiguous mice are not necessary assigned to the same hole?

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        10 days ago, # ^ |
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        The group of mice assigned to some hole is always contiguous, i.e. there will never exist a situation that a,b,c are three consecutive mice (in increasing order of coordinate) but a and c are assigned to hole-1 but b is assigned to hole-2.
        And what do you mean by how I deal with hole capacities? If I have to assign some suffix of the first x mice to hole j, then I can assign atmost the last capacity[j] mice to hole j.

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          10 days ago, # ^ |
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          Just a moment after I posted, I realized sorting was enough to assign contiguous mice to a hole.

          As for the hole capacities, yep, I meant that (and I missed it's as simple as that!)

          Thank you :)

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    9 days ago, # ^ |
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    Please also discuss the approach for problem E.

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12 days ago, # |
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Can someone please help me in finding mistake in my Solution for problem C.

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    12 days ago, # ^ |
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    Your code fails for this testcase : abcbabbcc

    Your code outputs aabbccbcb whereas the correct answer is aabbbcbcc

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12 days ago, # |
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Can someone tell me where I am wrong in D?

I made a fucntion checkValid which takes node,l,r as arguments. And marks true if value[node] lies between l and r both inclusive. Then, I call checkValid with left[node], and with the intersection of (-inf,value[node]-1) and (l,r). The same process is repeated symmetrically for right node.

I am getting WA at Test Case 20. And my answer differs by 1 from expected answer.

Submission Link: 26396243

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    12 days ago, # ^ |
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    There were two mistakes.

    One was a syntax error at line 92. Second mistake was I was remembering the nodes which are visited instead of values.

    AC solution: 26398128

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12 days ago, # |
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No successful submissions on E in Python 2 or Python 3. I tried to rewrite one Java solution to Python, it TLE-ed on test 7. Isn't the time limit of problem E too tight for Python?

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12 days ago, # |
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It's my first time to try hacking here on CF. Not sure how it works. It seems to be just stuck loading forever. Is this supposed to happen?

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    12 days ago, # ^ |
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    Reload

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      12 days ago, # ^ |
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      I tried reloading many times, and also clearing my browser cache/cookies before trying again. This happens after I submit the input for hacking by the way.

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12 days ago, # |
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Can anybody tell why my code is failing in one of the tests ?? https://pastebin.com/GC45xUAa

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    12 days ago, # ^ |
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    26389948

    ^This implementation is similar to yours. You can refer to this one.

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      12 days ago, # ^ |
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      Its quite confusing . He has considered even more cases . Can you read my code once and tell me , which case I might be missing ??

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12 days ago, # |
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That's how you try to cheat even in an unrated round!!

ScreenShot

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12 days ago, # |
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I noticed that if I submit a solution after a previous solution got hacked, then my new solution runs only the original system tests, and not the hack(s) that caught my previous solution(s). That's too bad, because that way I can be "Accepted" again without fixing my problem (in fact, I have no idea whether I fixed my problem unless the hacker is kind enough to keep trying the hack on my new solution).

UPDATE: Appears to be fixed now.

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12 days ago, # |
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http://codeforces.com/contest/797/submission/26402069 why this submission always wrong at 25th test case???who can help me ??

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12 days ago, # |
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Nice contest and nice problems

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11 days ago, # |
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My java solutions with proper documentation

Hope it helps.

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11 days ago, # |
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nice warm up round man....

thanks for all these... i luv this website <3

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11 days ago, # |
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I'm unable to submit a solution for the contest. It shows that System Testing is going on, while it was over hours ago.

On clicking the submit button, it shows the message "Practice is allowed only for finished and unfrozen contests".

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11 days ago, # |
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Is it normal that problems B and C now have duplicate tests? For example, there is the test #48 "1 // 1" that repeats further as #50, 51, and 54. Problem C also has such tests, e. g. "a" by #40, 41, 42, 45, 47, and 51.

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10 days ago, # |
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What is the logic behind problem E?