Codeforces celebrates 10 years! We are pleased to announce the crowdfunding-campaign. Congratulate us by the link https://codeforces.com/10years. ×

By arham_doshi, history, 3 days ago, In English,

hello i am arham doshi i want to take part in contest every day.but every day is not a contest day so i am thinking of take part in virtuals but if i can find a partner with whom i can take part in vc everyday and upsove next day it would be great for both of us.

so i am finding a friend preferably 1400 — 1700 . if you are interested plz comment .

ps: i want to take part i contest every day for 30 streak.it might help improve my rating and yours to.i have a blog about same and highly motivated about it. i am also looking for general friends :)

we are already 10 people so we cannot add more i you want i will keep posting link of vc that we give day 1 (26:feb) contest 841 day 2 (27:feb) https://www.codechef.com/UWCOI20 day 3 (28:feb) educational 1

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By 300iq, 41 hour(s) ago, In English,

Hello everyone, this winter at Petrozavodsk was my third (Petrozavodsk) contest, now it is loaded on the gym.

Contest link.

Virtual participation link.

Thanks to the testers MiFaFaOvO, ko_osaga, Radewoosh, ksun48, xiaowuc1, ainta, molamola., Endagorion, tEMMIE.w.

UPD: Editorial link

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Announcement of 300iq Contest 3
 
 
 
 
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By bigintegers, history, 17 hours ago, In English,

Recently, I learned about Tarjan and Kosaraju's algorithms to find articulation points.

However, I was wondering whether there are algorithms to find vertices whose removal disconnects the graph into three or more components (as opposed to two). I've searched online, and I cannot find anything (perhaps I'm using the wrong search terms?).

I have a guess, but I'm not sure if this is correct. I think that we can take the DFS tree, and conclude that a vertex satisfies my condition if one of the following is true:

1) It's the parent of the DFS tree with three or more children.

2) It's not the parent of the DFS tree with two children.

This seems too easy to me, so I'm pretty sure it's wrong.

Can someone please help me with this problem?

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By vovuh, history, 5 days ago, In English,

1311A - Add Odd or Subtract Even

Idea: vovuh

Tutorial
Solution

1311B - WeirdSort

Idea: MikeMirzayanov

Tutorial
Solution (n^2)
Solution (n log n)

1311C - Perform the Combo

Idea: vovuh

Tutorial
Solution

1311D - Three Integers

Idea: MikeMirzayanov

Tutorial
Solution

1311E - Construct the Binary Tree

Idea: MikeMirzayanov

Tutorial
Solution

1311F - Moving Points

Idea: vovuh

Tutorial
Solution (Fenwick tree)
Solution (pbds)

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By iyaad, 43 hours ago, In English,

-> Educational Codeforces Round 01 [ https://codeforces.com/contest/598 ]

-> Educational Codeforces Round 02 [ https://codeforces.com/contest/600 ]

-> Educational Codeforces Round 03 [ https://codeforces.com/contest/609 ]

-> Educational Codeforces Round 04 [ https://codeforces.com/contest/612 ]

-> Educational Codeforces Round 05 [ https://codeforces.com/contest/616 ]

-> Educational Codeforces Round 06 [ https://codeforces.com/contest/620 ]

-> Educational Codeforces Round 07 [ https://codeforces.com/contest/622 ]

-> Educational Codeforces Round 08 [ https://codeforces.com/contest/628 ]

-> Educational Codeforces Round 09 [ https://codeforces.com/contest/632 ]

-> Educational Codeforces Round 10 [ https://codeforces.com/contest/652 ]

-> Educational Codeforces Round 11 [ https://codeforces.com/contest/660 ]

-> Educational Codeforces Round 12 [ https://codeforces.com/contest/665 ]

-> Educational Codeforces Round 13 [ https://codeforces.com/contest/678 ]

-> Educational Codeforces Round 14 [ https://codeforces.com/contest/691 ]

-> Educational Codeforces Round 15 [ https://codeforces.com/contest/702 ]

-> Educational Codeforces Round 16 [ https://codeforces.com/contest/710 ]

-> Educational Codeforces Round 17 [ https://codeforces.com/contest/762 ]

-> Educational Codeforces Round 18 [ https://codeforces.com/contest/792 ]

-> Educational Codeforces Round 19 [ https://codeforces.com/contest/797 ]

-> Educational Codeforces Round 20 [ https://codeforces.com/contest/803 ]

-> Educational Codeforces Round 21 [ https://codeforces.com/contest/808 ]

-> Educational Codeforces Round 22 [ https://codeforces.com/contest/813 ]

-> Educational Codeforces Round 23 [ https://codeforces.com/contest/817 ]

-> Educational Codeforces Round 24 [ https://codeforces.com/contest/818 ]

-> Educational Codeforces Round 25 [ https://codeforces.com/contest/825 ]

-> Educational Codeforces Round 26 [ https://codeforces.com/contest/837 ]

-> Educational Codeforces Round 27 [ https://codeforces.com/contest/845 ]

-> Educational Codeforces Round 28 [ https://codeforces.com/contest/846 ]

-> Educational Codeforces Round 29 [ https://codeforces.com/contest/863 ]

-> Educational Codeforces Round 30 [ https://codeforces.com/contest/873 ]

-> Educational Codeforces Round 31 [ https://codeforces.com/contest/884 ]

-> Educational Codeforces Round 32 [ https://codeforces.com/contest/888 ]

-> Educational Codeforces Round 33 [ https://codeforces.com/contest/893 ]

-> Educational Codeforces Round 34 [ https://codeforces.com/contest/903 ]

-> Educational Codeforces Round 35 [ https://codeforces.com/contest/911 ]

-> Educational Codeforces Round 36 [ https://codeforces.com/contest/915 ]

-> Educational Codeforces Round 37 [ https://codeforces.com/contest/920 ]

-> Educational Codeforces Round 38 [ https://codeforces.com/contest/938 ]

-> Educational Codeforces Round 39 [ https://codeforces.com/contest/946 ]

-> Educational Codeforces Round 40 [ https://codeforces.com/contest/954 ]

-> Educational Codeforces Round 41 [ https://codeforces.com/contest/961 ]

-> Educational Codeforces Round 42 [ https://codeforces.com/contest/962 ]

-> Educational Codeforces Round 43 [ https://codeforces.com/contest/976 ]

-> Educational Codeforces Round 44 [ https://codeforces.com/contest/985 ]

-> Educational Codeforces Round 45 [ https://codeforces.com/contest/990 ]

-> Educational Codeforces Round 46 [ https://codeforces.com/contest/1000 ]

-> Educational Codeforces Round 47 [ https://codeforces.com/contest/1009 ]

-> Educational Codeforces Round 48 [ https://codeforces.com/contest/1016 ]

-> Educational Codeforces Round 49 [ https://codeforces.com/contest/1027 ]

-> Educational Codeforces Round 50 [ https://codeforces.com/contest/1036 ]

-> Educational Codeforces Round 51 [ https://codeforces.com/contest/1051 ]

-> Educational Codeforces Round 52 [ https://codeforces.com/contest/1065 ]

-> Educational Codeforces Round 53 [ https://codeforces.com/contest/1073 ]

-> Educational Codeforces Round 54 [ https://codeforces.com/contest/1076 ]

-> Educational Codeforces Round 55 [ https://codeforces.com/contest/1082 ]

-> Educational Codeforces Round 56 [ https://codeforces.com/contest/1093 ]

-> Educational Codeforces Round 57 [ https://codeforces.com/contest/1096 ]

-> Educational Codeforces Round 58 [ https://codeforces.com/contest/1101 ]

-> Educational Codeforces Round 59 [ https://codeforces.com/contest/1107 ]

-> Educational Codeforces Round 60 [ https://codeforces.com/contest/1117 ]

-> Educational Codeforces Round 61 [ https://codeforces.com/contest/1132 ]

-> Educational Codeforces Round 62 [ https://codeforces.com/contest/1140 ]

-> Educational Codeforces Round 63 [ https://codeforces.com/contest/1155 ]

-> Educational Codeforces Round 64 [ https://codeforces.com/contest/1156 ]

-> Educational Codeforces Round 65 [ https://codeforces.com/contest/1167 ]

-> Educational Codeforces Round 66 [ https://codeforces.com/contest/1175 ]

-> Educational Codeforces Round 67 [ https://codeforces.com/contest/1187 ]

-> Educational Codeforces Round 68 [ https://codeforces.com/contest/1194 ]

-> Educational Codeforces Round 69 [ https://codeforces.com/contest/1197 ]

-> Educational Codeforces Round 70 [ https://codeforces.com/contest/1202 ]

-> Educational Codeforces Round 71 [ https://codeforces.com/contest/1207 ]

-> Educational Codeforces Round 72 [ https://codeforces.com/contest/1217 ]

-> Educational Codeforces Round 73 [ https://codeforces.com/contest/1221 ]

-> Educational Codeforces Round 74 [ https://codeforces.com/contest/1238 ]

-> Educational Codeforces Round 75 [ https://codeforces.com/contest/1251 ]

-> Educational Codeforces Round 76 [ https://codeforces.com/contest/1257 ]

-> Educational Codeforces Round 77 [ https://codeforces.com/contest/1260 ]

-> Educational Codeforces Round 78 [ https://codeforces.com/contest/1278 ]

-> Educational Codeforces Round 79 [ https://codeforces.com/contest/1279 ]

-> Educational Codeforces Round 80 [ https://codeforces.com/contest/1288 ]

-> Educational Codeforces Round 81 [ https://codeforces.com/contest/1295 ]

-> Educational Codeforces Round 82 [ https://codeforces.com/contest/1303 ]

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By rng_58, history, 4 days ago, In English,

Unfortunately, due to the new Corona Virus problem, we decided to postpone WTF 2020. In Japan, various sport events were cancelled recently (for example football matches). We discussed internally, and concluded that WTF should be postponed too. We are very sorry for the late decision.

However, we hope to reschedule the event and hold WTF 2020 in the future. We will announce the schedule again when the situation gets better.

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By adedalic, history, 12 hours ago, In English,

1297A - Likes Display

Author: MikeMirzayanov

Editorial
Solution (elizarov)

1297B - Cartoons

Author: MikeMirzayanov

Editorial
Solution (elizarov)

1297C - Dream Team

Author: MikeMirzayanov

Editorial
Solution (elizarov)

1297D - Bonus Distribution

Author: MikeMirzayanov

Editorial
Solution (elizarov)

1297E - Modernization of Treeland

Author: MikeMirzayanov

Editorial
Solution (elizarov)

1297F - Movie Fan

Author: MikeMirzayanov

Editorial
Solution (elizarov)

1297G - M-numbers

Authors: MikeMirzayanov, Stepavly

Editorial
Solution (elizarov)

1297H - Paint the String

Authors: MikeMirzayanov, antontrygubO_o

Editorial
Solution (elizarov)

1297I - Falling Blocks

Authors: FieryPhoenix, dragonslayerintraining

Editorial
Solution (elizarov)

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By EmBeeZed, history, 45 hours ago, In English,

It turns out, that the final amortized time complexity is $$$O(α(n))$$$, where $$$α(n)$$$ is the inverse Ackermann function, which grows very slowly. In fact it grows so slowly, that it doesn't exceed $$$4$$$ for all reasonable $$$n$$$ (approximately $$$n<10^{600})$$$.

code

Question: Why this works in $$$O(α(n))$$$?

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By EmBeeZed, history, 16 hours ago, In English,

The inclusion-exclusion principle can be expressed as follows:

To compute the size of a union of multiple sets, it is necessary to sum the sizes of these sets separately, and then subtract the sizes of all pairwise intersections of the sets, then add back the size of the intersections of triples of the sets, subtract the size of quadruples of the sets, and so on, up to the intersection of all sets. The above definition can be expressed mathematically as follows:

It is intuitive for $$$n\leq 3$$$. But I have some problem with it. I cannot understand why it is like that?! (previously thanks!)

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By -is-this-fft-, history, 14 hours ago, In English,

Hi.

Sometimes I use Codeforces groups for private trainings. On occassion, this means importing (via Polygon) problems from some other contests (that have public test data and are free to be used like that).

But when importing test cases "from the files" or "from the archive", this happens a lot:
(By the way I have no idea why it happens so frequently. My best guess is sometimes that OI-style contests have to repeat test cases in different subtasks. But I have also seen this with ICPC-style.)

Anyway, my question is:

  • Why does Polygon even care if there are multiple equal tests? It doesn't seem to care if there are two equal tests from generators.
  • Why does it only show one error at a time, and a seemingly random pair at that (It doesn't seem like it is the "lexicographically smallest" pair)?
  • Can I somehow turn this validation off? There are some (probably more important) checks that you can turn off.

(I guess I should be smarter and write a local script to remove the duplicates).

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