F is shit.

9 months ago, # ^ |

+65

when asking for downvotes and asking for upvotes are unsurprisingly in the same SCC

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bycicle

9 months ago, # ^ |

-48

As a participant, I will have participated.

Spoiler for upvotes:

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9 months ago, # ^ |

+12

you've reposted in the wrong connected component

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9 months ago, # ^ |

→ Reply

User_Carrot

9 months ago, # ^ |

For not wasting time, the secret in lots of spoiler is help_me_please. :D.

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Greedious

9 months ago, # ^ |

← Rev. 2 →

+60

posting mind blowing meme to get upvotes :

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shivansh1102

9 months ago, # |

+60

As the leamder

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absolute-mess

9 months ago, # ^ |

+45

Domne

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anubhavdhar

9 months ago, # |

+52

As an author

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Tom66

9 months ago, # |

+30

Div 1+2 and 8 problems! Looking forward to it.

When will scoring distribution come out?

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physics0523

9 months ago, # |

As a tester, I just hope everyone's super-super-supercalifragilisticexpialidocious performance on the contest.

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glebustim

9 months ago, # |

+30

As not a tester, I did not test this round.

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BARBARIANNNNN

9 months ago, # |

-10

I want contribution, I also want rating, I can't have both of them, So I choose rating instead of contribution.

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DitaMirika

9 months ago, # |

← Rev. 2 →

+15

As a participant,I'm hoping for a great round!

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9 months ago, # ^ |

+14

As an author, me too.

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DitaMirika

9 months ago, # ^ |

Looking forward to it :p

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Karerp

9 months ago, # |

-16

Spoiler

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spydermonk

9 months ago, # ^ |

-10

okay

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9 months ago, # |

-262

As an author

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9 months ago, # ^ |

-8

omg that thumbs up emoji looks fabulous

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9 months ago, # ^ |

-21

also YOU SHOULDNT BRAINSTORM THE SOLUTIONS WITH OTHERS DURING CONTEST ITS AGAINST THE RULES

(yes, I couldn't believe my eyes after reading that line)

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9 months ago, # ^ |

-22

what's wrong with all this downvote, I'm just stating the facts. are they all cheaters or what

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9 months ago, # ^ |

-251

Come on dude! Isn't it obvious that, by "you guys", I meant everyone, brainstorm the solutions "individually"

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9 months ago, # ^ |

+76

Well, yes, except for the fact that brainstorming, in common sense and as stated on this wikipedia page, is a "group creativity technique". Using a group creativity technique where there isn't a group would be a pain...

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flakes24

9 months ago, # ^ |

got downvoted for being right

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silence0

9 months ago, # ^ |

now this is a comeback

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9 months ago, # ^ |

help me, this comeback has reversed somehow

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9 months ago, # ^ |

after the contest, I realized.

You (plural) might have tried your best to make the problems as interesting as possible, but you (singular) didn't! Shame on you!

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PolarFlea

9 months ago, # ^ |

F*ck you problem stoler.

Let's downvote him to make his contribution lower than zxyoi cuz it's the second time such situation happens

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AntiXoR

9 months ago, # |

← Rev. 2 →

IIT KGP !orz

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cf-coder

9 months ago, # ^ |

What is IIT KGP?

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drakeramoray27

9 months ago, # ^ |

+10

Indian Institute of Technology, Kharagpur. It's India's one of the best engineering institute.

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catch_me__if_you_can

9 months ago, # ^ |

-16

students of India's one of the best engineering institute. steal problems from online judges. Shame !!!

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ZyadFva

9 months ago, # |

As a pupil contestant

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Hamroz_JONN

9 months ago, # ^ |

Lol bro, u r on the edge of pupil-newbie

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Echp0chmak

9 months ago, # ^ |

and what's so wrong with it?

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ZyadFva

9 months ago, # ^ |

-8

i lost 70 points this round. now it's unrated i got my points back (Thanks god)

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whynesspower

9 months ago, # ^ |

why is it unrated?

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ZyadFva

9 months ago, # ^ |

one of problems was copied from another judge.

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allal

9 months ago, # |

I hope I can do at least the first one

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9 months ago, # ^ |

I guess we didn't bro xD

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actual_truthseeker

9 months ago, # |

is this contest real? last one vanished from the website with no notice...

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Omar_Hafez

9 months ago, # |

+91

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9 months ago, # ^ |

+38

When the guy who steals your meme gets more upvotes than you.

Reference: https://codeforces.com/blog/entry/102996?#comment-914421

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9 months ago, # ^ |

first time ?

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tiasmondal

9 months ago, # |

+50

Really happy to see IIT KGP finally setting contests in Codeforces. Kudos to the entire team of problemsetters.

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SalmaHatem_

9 months ago, # |

← Rev. 2 →

+10

I love div.1 + div.2 contests
Good luck for everyone!!
Hoping for a nice problems❤️

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nowadays-

9 months ago, # ^ |

Good luck

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islam231

9 months ago, # |

← Rev. 2 →

Is it rated for DIV 2 ?

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9 months ago, # ^ |

+14

Yes, it is rated for all divisions.

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9 months ago, # ^ |

not any more xD

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Noobish_Monk

9 months ago, # |

Hoping to solve 4 problems, would be great

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9 months ago, # ^ |

-259

Wishing you luck, to solve even more

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nowadays-

9 months ago, # ^ |

Hope you can solve more problems too

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Miyano_Shiho

9 months ago, # ^ |

I hate you. I absolutely do.

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Retired_Snow

9 months ago, # |

Hope to become as soon as possible Candidate Master.

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9 months ago, # ^ |

-266

All the best

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Pakgamer2022

9 months ago, # |

Great Way To Rate Up

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DailyFact2

9 months ago, # |

-15

But how will this affect Lebron's legacy?

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cuzperf

9 months ago, # |

As a xxx

Here is: hided content

The above comment is edited as follows:

<div class="spoiler">
  <b class="spoiler-title">As a xxx</b>
  <div class="spoiler-content" style="display: none;">
    <p>Give me xxx</p>
  </div>
</div>

Here is: <span style="color: white;">hided content</span>

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chicken_soup_is_coming

9 months ago, # ^ |

+32

However, A new comment will be shown in blue background

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Raito_Yagami

9 months ago, # ^ |

hidden content*

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tumhari_mummy

9 months ago, # ^ |

You can also do stuff like this

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9 months ago, # |

good luck everyone and hope the problems this time is not mathforces qwq

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9 months ago, # ^ |

some moderate amount of math is fine, last time it was kinda excessive but the problems were very interesting

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9 months ago, # ^ |

Yeah i agree

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pigmike

9 months ago, # ^ |

+23

god, you're everywhere

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logician_3_7_9

9 months ago, # |

-12

Contest time collides with IND VS AFG cricket match. Very unfortunate.

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hackerbhaiya

9 months ago, # ^ |

+22

It's IND vs SL!

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mr-strange

9 months ago, # |

All the Best EveryOne!

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nowadays-

9 months ago, # |

Good luck to all

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Hello-Tourist

9 months ago, # |

HA HA HA ......

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Ankit.Chauhan

9 months ago, # |

I would like to thank the authors in advance for another grid problem.

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Ahmed_AboRadwan

9 months ago, # |

Sometimes you win, sometimes you learn

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Here_I_Go420

9 months ago, # |

Wishing everyone high rating!!!

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9 months ago, # |

We just got trolled

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9 months ago, # |

How to solve D?

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MainuCodingBadiPasandAe

9 months ago, # ^ |

← Rev. 2 →

Is it MST (here any spanning tree would do)? I was finding a set of edges for the MST and color them, and color the remaining edges with the other color. And maybe in case of cycles for the second coloring, we could swap some edges. But wasn't able to implement this (because the idea isn't clear to me either)

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dulatcodes

9 months ago, # ^ |

← Rev. 2 →

Color everything in blue. Now do a DFS from node 1. Since m is at most n+2, you will get at most 3 back edges. Store those back edges while traversing by dfs.

Now you have obtained some tree rooted in node 1, with some back edges. Now if you have less than 3 back edges, simply color those back edges as red.

If you have 3 back edges, and they form a triangle, in other words have form a-b, b-c, a-c, color a-b and b-c as red. Now look at a-c. Coloring this as red would be a waste, because a, b, c are already connected. So instead leave it as blue. Find out whether a or c has a greater depth in the DFS tree. Let’s say d = deepest(a, c). Color the edge d and parent[d] in red. This way we preserve the tree structure of the blue subgraph and decrement the number of connected components in the red subgraph.

If you have 3 back edges that do not form such a triangle/cycle. Just color them in red.

I highly suggest drawing a tree structure with back edges to understand it better.

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Saucemaster102

9 months ago, # |

+17

C was so good :D

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AlexMari

9 months ago, # |

Very goood problems A, B, C!

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Ayanokouji

9 months ago, # |

How to solve C? Any hints

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ELDRVD

9 months ago, # ^ |

Look at number of index i, such that s[i]='(' and s[i+1]!=')'

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9 months ago, # ^ |

or you can just count '))'s in $$$(s)$$$

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9 months ago, # ^ |

I just use DSU.

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9 months ago, # ^ |

← Rev. 2 →

How is its time complexity?

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9 months ago, # ^ |

I don't calculate but get only 31 ms.

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9 months ago, # ^ |

← Rev. 2 →

+22

oh. that's fast. maybe the time complexity is $$$O(\text{fastenough})$$$.

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Ayanokouji

9 months ago, # ^ |

← Rev. 3 →

DSU here how? If you could explain your thought process it would be helpful

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pribic

9 months ago, # ^ |

suppose you are at a closing bracket. Then it will have a matching opening bracket as well. Link those two indexes in dsu. Lets say matching opening bracket is at i. Then if i-1 position also contains closing bracket then merge i and i-1 as well in dsu.

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9 months ago, # ^ |

I use DSU and at the last step count the different number or parent.If make count+1 at '(' and count-1 at ')' you will see that all i for 1 to 2*n where count =1 or count=0 are conected. I use this obserbation to solve. Sorry for my poor English.

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robostac

9 months ago, # ^ |

Link every opening bracket to it's corresponding closing bracket. Whenever there is a ")(" in the string link those two brackets to handle the "()()" case where 1 needs to connect to 4.

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sjain8078

9 months ago, # ^ |

i also used the same approach but i was getting TLE, could you please share your approach/solution?

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doraty228

9 months ago, # ^ |

the number of positions such that s[i] = s[i+1] = ')'

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hzr

9 months ago, # |

+233

F is shit.

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Lightnessqwq

9 months ago, # ^ |

+73

Can't agree more.

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9 months ago, # |

Problem C was nice.

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9 months ago, # ^ |

Wut it's easier than A, I'm mad because of B not saying it's hard but I'm so stupid and slow

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9 months ago, # ^ |

me here, getting 150 on A :(((((((((((((((

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9 months ago, # ^ |

Good sir, can I know how you made that observation for C?
I have never been so mad at a problem T-T

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9 months ago, # ^ |

I noticed that () () () for example is all connected then I assumed that all of are disconnected and everytime i see () then this one is connected to another sequence

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9 months ago, # ^ |

"I assumed that all of" you mean 'other' instead of 'of', right?
Also, Thanks but I don't know why I couldn't think of this. Would it be lack of practice of 1400-1500 rated problems?

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9 months ago, # ^ |

It needs some luck i may haven't noticed it but if we are trained on graphs it won't be a problem

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9 months ago, # ^ |

I see, thanks once again :D

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9 months ago, # ^ |

I JUST use DSU and at the last step count the different number or parent.If make count+1 at '(' and count-1 at ')' you will see that all i for 1 to 2*n where count =1 or count=0 are conected. I use this obserbation to solve. Sorry for my poor English.

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9 months ago, # ^ |

Thank you! I guess having a bit more knowledge of dsu might have helped ;(

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9 months ago, # ^ |

It doesn't need any of that just a for loop would work

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9 months ago, # ^ |

Yea true, what I actually meant was, maybe knowing dsu well might have given me a different perspective because I couldn't make that observation.

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9 months ago, # ^ |

← Rev. 2 →

here's my crude drawing during contest for C, if it might help:

notice how the component count increases for every two decreasing (or increasing, as others pointed out) steps in a row.

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9 months ago, # ^ |

Ohh nice, I will try this idea after few days and see if I can get the approach. Honestly, what I did was to notice the how deep the opening bracket's are going and counted them.
For eg. ( ( ( ) ) ), depth was 2.

And for this ( ( ) ) ( ( ) ), the depth for both first and second balanced sequence is 1. So, it becomes 2 and added 1 for the remaining component. And, it even passed for all given TCs, which made me believe theres something wrong in the code and not in observation.

I get riddled in my own ideas ;-;

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strgglr

9 months ago, # ^ |

What i thought is when the string is ((())) complete then the answer is n but the time you take out a () outside, a component decreases. So calculate no of instant parenthesis. We already have 1 instant parenthesis in the starting case. So answer will be n-(instant-1).

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9 months ago, # ^ |

Ohh wow, this actually makes sense to me. Wish I would have thought a bit in this direction.
Alsoo, Congrats on specialist!!

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mukulrawat_03

9 months ago, # ^ |

i messed up preety badly at c

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9 months ago, # |

+40

Problem F is boring and hard to implement :(

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shauryasinha020

9 months ago, # ^ |

Any hints for D?

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9 months ago, # ^ |

The connected components are trees.

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drdilyor

9 months ago, # ^ |

← Rev. 2 →

Could you explain how to find spanning tree such that remaining 3 edges don't form a cycle( triangle )?

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9 months ago, # ^ |

+30

Random algorithm .

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nidaboge

9 months ago, # ^ |

How to solve d with random algorithm

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https://codeforces.com/blog/entry/106586?#comment-950389

9 months ago, # ^ |

→ Reply

ikaurov

9 months ago, # ^ |

+34

Determenistic solution: Do a DFS, for every vertex record parent and depth in DFS tree, find the 3 additional edges. If the edges do form a cycle, take any of the 3 edges (let's say (u-v), where depth[u] > depth[v]) and replace it with edge (u-parent[u]).

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thatsramen

9 months ago, # ^ |

+32

Find any tree, then, if the remaining edges form a cycle, build a new tree with one edge of this cycle in it. It will guarantee that the new tree is ok.

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ELDRVD

9 months ago, # ^ |

Nope, for an example, in test case 2, you have one connected component and it is cycle.

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9 months ago, # ^ |

I mean the connected components formed by same color.

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ELDRVD

9 months ago, # ^ |

← Rev. 2 →

Oh, okey when.

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9 months ago, # ^ |

By the way , The $$$O(n\times \sqrt{nlog_2n})$$$ solution may be easier to implement.

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9 months ago, # ^ |

FST now :(

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shauryasinha020

9 months ago, # |

hints for D?

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z1bbo

9 months ago, # ^ |

← Rev. 3 →

I also failed it, my approach was this:

use union find to color all red without loops
at the end at most 3 blue edges will be left over
if those three blue edges happen to form a loop, swap the last blue edge with one of the red edges -> there will be no blue loop any more
my problem was I didn't know how to select the correct red edge to swap with, since for some red edges you will create a red-cycle

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shadow9236

9 months ago, # ^ |

You have to check if the edge you are changing from blue -> red should not be between an ancestor and child in the red tree

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Wielomian

9 months ago, # ^ |

Hint 1

Hint 2

Hint 3

Solution

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9 months ago, # ^ |

How is this optimal?

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Wielomian

9 months ago, # ^ |

Each edge has to decrease number of either red components or blue components, and it can only decrese one of those by exactly 1. Thus, the optimal value is $$$2 * n - m$$$. In case of there not being a triangle we have exactly this value with the above method. In case of triangle also this value, but it's a little bit harder to see.

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gyh20

9 months ago, # |

← Rev. 2 →

+34

Defeated by the memory limit of problem F.

I wrote a segement tree without optimizing anything in the last minutes, using the memory of $$$O(n\log n)$$$. When I noticed the memory limits I didn't have time to make a change.

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dl720125

9 months ago, # ^ |

+10

Same here. 256MB is unnecessarily too tight! Lose the chance to gain rating.

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tzc_wk

9 months ago, # ^ |

+20

My ST table didn't get MLE.

However, I forgot to check whether there's a time which can reach n without passing any red lights and got WA on test 7. What a pity.

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Prakhar1998

9 months ago, # |

What is the expected time complexity for D?

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algoboi

9 months ago, # |

← Rev. 2 →

Can we solve D by randomizing? My idea is you only need to randomize m — n + 1 edges, and check if any of the two sets create a cycle. m-n+1 is at most 3 so it should be fast enough?

The proof of correctness is that, if the graph is a tree, obviously it makes no difference how the edges are allocated. If we have extra edges, then every edges will reduce the connected component by 1, so we make a tree for the blue, and the rest for red, as long as they are both trees.

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shadow9236

9 months ago, # ^ |

+12

Make MST. Pick the $$$m-(n-1)$$$ edges not in MST. Only when $$$m = n+2$$$ can these edges create a cycle. If they do, then take one edge and transfer it to other color and the edge to its parent to current color, provided that the swapped edge is not in its subtree.

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Odysseus96

9 months ago, # ^ |

← Rev. 2 →

I had the same idea but I don't know how to implement it.

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koqo

9 months ago, # |

What is a 'connected component' in Problem D? In the first example, it says blue edges form 2 components, but I only see 1.

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9 months ago, # ^ |

$$$1,2,3,5$$$ was one component, $$$4$$$ was the other

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koqo

9 months ago, # ^ |

← Rev. 2 →

Thanks, I understand the problem now, have to consider all the vertices and not just the ones connected by the specific colored edge.

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feecIe6418

9 months ago, # |

+41

F is so annoying to implement (256MB memory limit makes it even worse!). But D and E are interesting.

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9 months ago, # ^ |

← Rev. 2 →

How to solve E? I thought its about calculating sums of $$$\frac{P^n_{2k}}{2^k k!}$$$ or smth for $$$1\leq k \leq \lfloor \frac{n}{2} \rfloor$$$

(sorry about the big text, things were becoming unreadable)

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bajablast

9 months ago, # ^ |

Yeah, the way you do that subproblem is by thinking about it conceptually instead of combinatorially. You're trying to find the ways to pair some elements from n things. This can be written as a dp[n] = dp[n-1] + (n-1)*dp[n-2] (you either pair the first element with something, or u don't), which can be precomputed before you do the loop over number of 4-cycles.

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9 months ago, # ^ |

Instead of permutations I thought about the problem with cycles (by building the graph of the permutation). To be almost perfect, cycles either have length 1 (pointing to itself) or length 2 (pointing to each other) or length 4, see picture. Rest was combinatorics. I will link my solution after the grading finished (was 7 minutes too late sadly...). I iterated over the amount of length-4 cycles.

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9 months ago, # ^ |

← Rev. 2 →

OHHHHHHH. I was thinking about cycles too, in this process I came up with that formula. totally missed the length-4 cycles though. E was a good problem after all!

→ Reply

9 months ago, # ^ |

171160691.

First I calculated $$$P_i$$$ by this recursion: $$$P_0=1$$$, $$$P_1=1$$$, $$$P_i=P_{i-1}+(i-1)\cdot P_{i-2}$$$. This is the amount of partitions of $$$i$$$ elements into sets of size $$$1$$$ and $$$2$$$.

Then we calculate the following:

$$$\sum_{i=0}^{4i\le n} \binom{n-2i}{2i} (2i-1)!! \cdot 2^i P_{n-4i} $$$

The sum goes over the amount of length-$$$4$$$ cycles. The binomial calculates how many different distributions for $$$2i$$$ neighbouring 2-tile-pairs there are. The Double Factorial is the amount of combinations to form $$$4$$$-tile-cycles by choosing $$$2$$$ each from the previously distributed $$$2$$$-tile-pairs. Each $$$4$$$-tile cycle then can have 2 different orientations, so we need to multiply by $$$2^i$$$. Then $$$P_{n-4i}$$$ is the amount of combinations to form $$$1$$$ or $$$2$$$ tile pairs from the remaining nodes.

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9 months ago, # |

← Rev. 7 →

why getting TLE at problem B? someone help me

t = int(input())
while t>=1:
    n,m = map(int,input().split())
    if m<n:
        print("No")
 
    elif n%2 == 0 and m%2 !=0 :
        print("No")
 
    else:
        ans = []
        if n%2 !=0:
            ans = [1] * (n-1)
            a = m - (n-1)
            ans.append(a)
        else:
            ans = [1] * (n-2)
            a = (m - (n-2))//2
            ans.append(a)
            ans.append(a)
 
        print("Yes")
        for i in range(len(ans)):
            if i == len(ans)-1:
                print(ans[i])
            else: print(ans[i],end= " ")
    t-=1

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Nikhil19259

9 months ago, # ^ |

@u1602016 You are not decrementing variable t, so it continues to loop forever :)

→ Reply

9 months ago, # ^ |

oops sorry,last line just got canceled while copy pasting the code.still getting TLE

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Nikhil19259

9 months ago, # ^ |

Can you share the your original submission link?

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9 months ago, # ^ |

Yeah sure https://codeforces.com/contest/1726/submission/171148335

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Varad

9 months ago, # ^ |

use sys module for input, here's my solution- https://codeforces.com/submissions/Varad2002

→ Reply

9 months ago, # ^ |

thanks a lot @varad2002

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Varad

9 months ago, # ^ |

You’re welcome :)

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savsmail

9 months ago, # ^ |

Same problem. TLE with Python/PyPy3 (pretest 4), OK with C++ (system testing). Slow input/output in Python, maybe.

Is it possible to get pretest 4 for experiments?

Submission https://codeforces.com/contest/1726/submission/171110352 Room (with the other submissions with slightly smodified input/output) https://codeforces.com/contest/1726/room/464

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pajenegod

9 months ago, # ^ |

The way it works is that the input function in Python calls sys.stdout.flush. So everytime you call input you flush stdout, which can be really slow. The way to get around this is to use sys.stdin.readline instead of input. Worth noting is that input internally calls sys.stdin.readline.

If you take a look at C++ submissions will probably see cin.tie(0), which is how you turn off this very same feature in C++.

Knowing how to avoid flushing can be very useful in general. For example your (savsmail) C++ submission speeds up by a factor of 16 by avoiding to flush 171253842 .

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savsmail

9 months ago, # ^ |

Wow, that explains a lot. Thank you!

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Nikhil19259

9 months ago, # ^ |

@u1602016 yes, the problem is with the slow I/O in python as it takes 5-10 times more to run compare to c/c++.

For the cross-check part I have also converted your solution in c++, and tried to submit, and it works perfectly fine within time(561ms, note: your solution is correct) here

Solution??? you could either use the fast I/O for python while doing CP (as @Varad2002 mentioned) or you could use c++ for CP (I would personally recommend this, as I have experienced the situation where my JAVA code throws TLE (even after using fast I/O) whereas same algorithm works within time limit in C++)

→ Reply

9 months ago, # ^ |

thanks a lot for your [email protected]

→ Reply

d_sqaure

9 months ago, # |

I couldn't enjoy this contest :(, might be very clever problems.

→ Reply

Rikitexh

9 months ago, # |

hint for c?

→ Reply

NO__OB

9 months ago, # ^ |

)(

→ Reply

Rikitexh

9 months ago, # ^ |

← Rev. 5 →

Spoiler

→ Reply

9 months ago, # ^ |

+12

Spoiler 1

Spoiler 2

Solution

→ Reply

faizanhussain2310

9 months ago, # ^ |

Was this easy to catch this observation as i tried to solve trivally by making DSU but not able to do it

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9 months ago, # ^ |

← Rev. 2 →

Phew, well, depends on your understanding of easy. As I was solving the problem, the Spoilers/Solution which I posted reconstruct my thought process. And I'd say I have noticed them pretty quickly. I didn't even consider building the graph explicitly (and using DSU or similar) yet.

I guess the first thing you want to do is find observations about the structure of the problem. Only if you can't find any structure, you take out the harder techniques. And then try to find structure on the harder techniques. And always user pen and paper!

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Theo830

9 months ago, # |

Any hints for E?

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bajablast

9 months ago, # ^ |

Look at cycle decomposition of $$$p$$$.

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TanSinTheta

9 months ago, # |

Really nice problems ! Keep it up authors ^_^

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rgnerdplayer

9 months ago, # |

+16

D: randomly color all edges. Break if both colors do not form cycles.

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9 months ago, # ^ |

+20

We tried our best to break such solutions, but it seems it was not enough :(

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rgnerdplayer

9 months ago, # ^ |

+13

I would like to know how to break (or attempt to) these kind of solutions.

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9 months ago, # ^ |

My attempts were primarily focused on maximising the number of tests, with $$$n+2$$$ edges in every case, with graphs of ~1e3 (I think?) size. So mostly randomisation. I didn't have much hope of blocking everything because of the small number of extra edges compared to the number of possible spanning trees. If anyone has better ideas, I would be very interested to know...

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Radewoosh

9 months ago, # ^ |

+21

Break? Isn't that correct?

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9 months ago, # ^ |

Some of our testers' solutions using the same idea didn't pass, so I assumed it is incorrect.

Of course, if the number of iterations are sufficient it should pass with high probability. Admittedly, I did not do a thorough analysis of a randomised solution because the model solution does not use randomisation.

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Radewoosh

9 months ago, # ^ |

+17

Well, this one looks way simpler than anything with some logic inside. I'm talking about the version with a guess that we can achieve maximum possible score ($$$2n - m$$$) and we repeat until we succeed.

The intuition for me was that if it's anyhow hard/not straightforward to color the edges so that there are no cycles, these additional edges (yes, it's relative which ones are additional, but I'm talking about kind of a part of the graph in which something interesting happens) have to be close to each other, so the "hard" part of the graph is small, so there are not so many possibilities and we will find good one quickly.

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9 months ago, # ^ |

← Rev. 2 →

I did this: Colored red if nodes are in different disjoint sets, blue otherwise. However, for m=n+2, there is a possibility of a cycle of 3 formed.

In that case, I made this observation: Suppose the 3-cycle is ABC then there is a node in A,B,C say A, such that AB and AC are connected using red. Then just take the last edge in the AB red path and make it blue, and make AB(blue) as red. It can be seen that this removes cycles in both red and blue.

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9 months ago, # ^ |

Why the downvotes?

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sontosh37271

9 months ago, # |

← Rev. 2 →

-38

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9 months ago, # |

Really enjoyed the contest, especially because all the questions were not only mathematics based. Also, waiting to submit D, solved just after the time ended. Same thing happening for the second time :')

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9 months ago, # ^ |

+16

D accepted in 1 go after the contest :')

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9 months ago, # |

+16

Code of Problem C <<< Solving Problem C

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9 months ago, # |

-13

wait what the heck

Spoiler

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M_bolshakov

9 months ago, # |

-14

I had to gain only 2 points to reach CM, and solved D on paper, started coding it more than 1 hr before the end, but in the end got TL 9 because i use maps which work slow. But my idea was fully correct. Now end up losing 7 points, and only 9 will be left before CM. this is fucking disqusting, it will be already 5th time when i have <10 points bafore CM!

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palindroam

9 months ago, # ^ |

Oh :/

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ALILILILILI-KHAN

9 months ago, # |

Isn't $$$1.205710448301$$$ the answer for the first sample in H? I've checked that in geogebra and it seems to be so.

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9 months ago, # ^ |

← Rev. 2 →

Are you sure it's the first sample? I mean to say, you don't mean the second sample by any chance, right?

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ALILILILILI-KHAN

9 months ago, # ^ |

← Rev. 2 →

I think so, here's the geogebra link: we are looking for the area bounded by $$$AB$$$, $$$AC$$$, and the circle passing through H and center O.

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Artyom123

9 months ago, # ^ |

+26

The area is bounded by a curve, but not an arc

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9 months ago, # ^ |

If you are using a circle as an envelope for the red part, that's incorrect. The curve is not a circle.

Check this: Click here

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ALILILILILI-KHAN

9 months ago, # ^ |

Oh I see, thanks

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Yahia_Emara

9 months ago, # |

← Rev. 2 →

My solution to problem C passsed system tests, Even though I am pretty sure its so different from the intended solution

I solved with a sparse table and DSU, I am interested to know if the solution is correct and actually fast enough (I am 99% sure its fast enough but I don't know about its validity)

Can Someone Verify?
Submission : https://codeforces.com/contest/1726/submission/171128759

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9 months ago, # ^ |

-8

do note that a lot of the faster ones (usually in Div1) solved it with DSU

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dream7

9 months ago, # ^ |

I too solved it using seg tree and DSU.

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Cooper1214

9 months ago, # |

Back to back bad performance from me, hope I can bounce back soon. People who are in a phase like me, "This shall pass too" :)

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9 months ago, # ^ |

thanks bro, you are my ray of hope (:

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9 months ago, # |

← Rev. 2 →

Check out this ridiculously easy solution for C: 171112911 (don't pay attention to that bin_power_of_two function — I forgot to delete it)

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9 months ago, # ^ |

The interesting thing is that I haven't found any of the red guys yet who would have approached the problem the same way.

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9 months ago, # ^ |

yes, because for them, the simpler (in the sense of observation) DSU implementation came first in mind.

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9 months ago, # ^ |

Could you explain the DSU solution?

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9 months ago, # ^ |

they just constructed the DSU like how they would do a normal graph and counted the components like how they would do a normal graph. only tricky part is what to merge and that's it

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rgnerdplayer

9 months ago, # ^ |

-8

171072071

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9 months ago, # ^ |

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9 months ago, # ^ |

literally ('('+input()+')').count('))') in python.

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9 months ago, # ^ |

Absolutely

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9 months ago, # ^ |

Even this works

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9 months ago, # ^ |

    ll ans=1;
    forsn(i,1,2*n){
        if(s[i]=='(' && s[i-1]=='(') ans++;
    }

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7_7

9 months ago, # |

-10

These unfamiliar names kinda throw me off the track. Wish we could use simpler names

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9 months ago, # |

If the current problem C(bracket sequence) were problem A, would it have been as difficult as it is now?

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bot747

9 months ago, # |

what a contest wasnt able to solve a single problem

aah my life is a lie

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9 months ago, # ^ |

same here xD

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9 months ago, # |

My exactly same code got ac after system test

AC code : https://codeforces.com/contest/1726/submission/171155848 TLE code : https://codeforces.com/contest/1726/submission/171146706

code was same compiler was same.... Just for system test load my code got tle...Please @authors do something about this...MikeMirzayanov please do something

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9 months ago, # ^ |

-10

code was same, compiler was same, the difference is the seed

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9 months ago, # ^ |

what is seed?

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9 months ago, # ^ |

← Rev. 2 →

-10

the seed is the value an RNG uses to start with. in your code this is chrono::steady_clock::now().time_since_epoch().count(), which varies by when the submission is run.

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9 months ago, # ^ |

I haven't used rng anywhere in my code...so it was not my fault at all.

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9 months ago, # ^ |

-10

oh, didn't notice it. turns out that your code barely just fit into the TL. I think you would've gotten hacked if this happened during competition, though.

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9 months ago, # ^ |

can you do something ? Newtech66

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MrOtter

9 months ago, # ^ |

+15

Do you really think 1996ms solution for 2s problem is correct?

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9 months ago, # ^ |

-7

How should I calculate this in contest time? Pretests got passed and even system tests too. But the judge load caused me TLE. Whats my fault here?

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dorijanlendvaj

9 months ago, # |

← Rev. 2 →

+116

On A, I saw a solution which initializes the answer with $$$|a_n-a_1|$$$ and, while I could've simply made a test case which breaks that solution very obviously, I instead decided to make fun of the pretests by hacking it with a test case of 50 tests with $$$n$$$ being a random number between $$$1$$$ and $$$6$$$ and $$$a_i$$$ being random numbers between $$$1$$$ and $$$10$$$. While most obviously wrong solutions like the one I hacked FSTd due to hacks specifically made against such solutions, this test case of 50 random tests also unintentionally caused FST of almost 100 solutions that don't work if a test with $$$n=1$$$ has a test right before it such that $$$a_2$$$ of the test right before the test with $$$n=1$$$ is greater than $$$a_1$$$ of the $$$n=1$$$ test.

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9 months ago, # ^ |

-13

LOL that is awesome. this is a legend, as you are too

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Khedr

9 months ago, # |

← Rev. 2 →

what is the approach in D and why DSU?

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toam

9 months ago, # |

+23

Why is the D's constraints so big? I can't understand why sum of N is 1e6. It is hard for python... (I passed pretest but got TLE on system test)

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9 months ago, # ^ |

It was because we were attempting to block randomised solutions. I'm sorry about the situation with Python being too slow >_<

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FynjyBath

9 months ago, # ^ |

← Rev. 2 →

I caught TL52 on the task D (https://codeforces.com/contest/1726/submission/171125630). After contest I sent the same solution again and it got Accepted (https://codeforces.com/contest/1726/submission/171157258). How did it happen? (>2 seconds vs 1.7 seconds)

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Kyou_mo_kawaii

9 months ago, # ^ |

I didn't know randomized wasn't intended. Is this hackable? https://codeforces.com/contest/1726/submission/171121286

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shivam_360

9 months ago, # |

Done C with DSU... how u guys come up with so easy solution...

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9 months ago, # ^ |

-13

observation, but observation isn't all so easy. observation comes along with experience as well

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faizanhussain2310

9 months ago, # ^ |

I am not very comfortable with these graph problem as you can see from my rating that i havent encountered many graph problems till now . Do these graph problem usually have these kind observation asking wrt C

And please guide my what i should do to reach specialist as while practicing i am comfortable upto *1500 problems but during contest i keep on getting stucked on problem C which are usually in the range of *1400 to *1600

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https://codeforces.com/contest/1726/submission/171146699
https://codeforces.com/contest/1726/submission/171158814

9 months ago, # ^ |

I am not very comfortable with these graph problem

So am I! This was a different case though. I just drew some parentheses strings with pen and paper, like '(' = rising slope, ')' = falling slope. Then I connected what I needed to connect based on the statements. After that, it was a long phase of thinking, thinking hard. Usually time for thinking > time for coding, this is very normal. Accepting this is one crucial step to Specialist, imho.

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geranazavr555

9 months ago, # |

+10

Ratings updated preliminarily. We will remove cheaters and update the ratings again soon!

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Pirated_Codes

9 months ago, # ^ |

thanks thanks thanks so much.

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ppps

9 months ago, # |

← Rev. 2 →

Got Accept with FST code for D.
Why is this so slow? It's just O(NlogN) and N <= 1e6
Can someone explain?

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9 months ago, # ^ |

Same happened to me and costed me losing CM. @admins should look at this.

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omeganot

9 months ago, # ^ |

maybe try having a function fix(pair p) that returns a sorted pair(smaller element before larger element). idk if it fixes your solution but it did work for my friend

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pooty

9 months ago, # |

+18

Btw, I FST for D, but when I try to resubmit the exact same code, it passes (barely). Is it possible to reverse the FST?

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earl_of_byteland

9 months ago, # ^ |

Faced the same issue. Not sure if they will take it into consideration, but I hope they do.

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dr.bae

9 months ago, # |

← Rev. 2 →

Hello everyone, I'm a newbie participant. On problem A, although it runs perfectly on my computer, I got runtime error. How Can I fix this problem? I copy my code below. Thank you. (I use Microsoft Visual Studio BTW)

#include <iostream>

using namespace std;

int main() {

	int t;
	int n[1000];
	int s;
	int qr;
	int zr;
	int result;

	cin >> t;

	while (t--) {
		
		cin >> s;

		for (int i = 0; i < s; i++) {

			cin >> n[i];
		}

		for (int z = 0; z < s; z++) {
			
			for (int q = z; q < s; q++) {

				if (n[z] > n[q]) {

					zr = n[z];
					qr = n[q];
					n[z] = qr;
					n[q] = zr;

				}
				else {
					continue;
				}
			}
		}
		if (s == 1) {
			result = 0;
		}
		else {
			result = n[s - 1] - n[0];
		}

		cout << result << endl;
	}

	return 0;
}

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lazy_loop

9 months ago, # ^ |

you need to increase the size of array. notice n<=2000 but you have declared an array of size 1000 only

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Rely_on_Allah

9 months ago, # |

After decades of the contest, Benq is on the top! Happy to see this (❁´◡`❁)

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javad_asadi

9 months ago, # ^ |

He didn't get the rating, though.

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mohaisber52

9 months ago, # |

Just a shit

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9 months ago, # |

Before I sleep,I saw my name turn green..What F???

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9 months ago, # ^ |

Unrated competition is not as good as virtual participation(hh)

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Swadia

9 months ago, # ^ |

Because F!!!

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9 months ago, # ^ |

You know that a person with blue even purple name are not able to solve this problem

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kanaluvu

9 months ago, # |

lol everyone is downvoting this post and the editorial.

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beethoven97

9 months ago, # ^ |

And even the comments, XD.

Spoiler

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miacul_cheater_buster

9 months ago, # |

-15

The coding club of IIT KGP is gonna face a lot of disrepute now becoz of you guys

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d_sqaure

9 months ago, # ^ |

Exactly , they may set 7 problems instead of 8 and time for 2 Hours would be better.

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shivansh1102

9 months ago, # |

← Rev. 2 →

+58

A sincere request to everyone!

Newtech66 and anubhavdhar have worked really hard for this round and they weren't aware of what happened in problem F. If you don't like the problems(except F), feel free to downvote the blog, but please refrain from doing so if this is the only reason! It would be very unfair and unjustice with them :(

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pigmike

9 months ago, # ^ |

-38

This is bullshit. I support downvoting the blog post because of F, it's high time all the authors start asking their co-authors how they developed the problems, so situations like this don't repeat. Every author of the round should be held equally accountable for each problem, and the round in general.

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https://codeforces.com/blog/entry/106700

9 months ago, # |

← Rev. 2 →

-6

oh after a night(in China), so many people downvoted the post

lol

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TrupalPatel

9 months ago, # |

-8

where is my ratings for this contest.

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CrackLewis

9 months ago, # ^ |

unrated because of a problem dupe

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CrackLewis

9 months ago, # ^ |

ppl downvotes for literally no reason lol

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huyulong

9 months ago, # |

Why this contest is Unrated?

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arash.

9 months ago, # ^ |

Problem F was a stolen problem.

The discovery

The announcement

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huyulong

9 months ago, # ^ |

Thanks!

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MostafaM.Galal

9 months ago, # |

my rating where is gone?!! i just reached pupil pls any information?

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Esomer

9 months ago, # ^ |

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MostafaM.Galal

9 months ago, # ^ |

-6

this is unfair who are they truly punishing if the author is cheater and has no morals why would he care if the round is rated or not he is just punishing the participants in fact there is a part of the problem on those who host contests the must make sure that the problem set is unique

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