k790alex's blog

By k790alex, history, 17 months ago, In English

Hi,

The 2019 ICPC Mexico Finals starts in 30 minutes.

Let's discuss the problems after the contest.

There are some mirror contests starting 1h after the real one:

This facebook page is posting updates frequently: https://www.facebook.com/acmitesochapter

Streaming:

Good luck to all the teams.

UPDATE The contest has started.

UPDATE Live scoreboard: https://global.naquadah.com.br/boca/score/index.php (use this if the previous one doesn't work https://global.naquadah.com.br/boca/scoreglobal.php?h=AT2oE0HBeAg8eox30q5wZOdk8SY_bIZ-hGKuX9OTrY661HqiWgHRra4KBYyrxV6IDqZeTVr7yJ6EpBVje50BxzQBkGZoTKMNPwb3UZpD_G79M9PmveqUhUUrtO04BJUpMwqPvrz_7o-QWTc)

UPDATE Problems available:

UPDATE Official results are ready: http://scorelatam.naquadah.com.br/

Congrats to the winners!!!

Ranking

UPDATE These are the teams going to the world finals, there were 4 extra spots:

- UH++,CUBA - Limitless, CUBA (new) - Norman is Hunting, MEXICO - E3, MEXICO - #define TriLCI(404.0) :v, MEXICO - pu+os, MEXICO (new) - Guerreros de RodriGOD, COSTA RICA - InChaVoLa, ARGENTINA - GG Dem, ARGENTINA - #NuevaConstitución UChile1, CHILE - Rating MiSeRable, PERU (new) - descomUNAL, COLOMBIA - La bomba de tenedores, VENEZUELA - Time com T, BRASIL - Campinas Grande, BRASIL - Amigos do Beto, BRASIL - Rock Lee do Pagode Namora D+, BRASIL - Rábalabaxúrias, BRASIL - Triple G, BRASIL (New)

UPDATE MarcosK uploaded the contest and the official standings to the gym: 2019-2020 ACM-ICPC Latin American Regional Programming Contest

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By k790alex, history, 2 years ago, In English

Hi,

I want to share the Java library that I used for programming contests, hopefully it is useful for someone: https://github.com/AlexITC/programming-contests-library

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By k790alex, 3 years ago, In English

Hi,

Tomorrow is going to be held The 2017 ACM-ICPC Mexico and Central America Finals (https://icpc.baylor.edu/regionals/finder/mexico-central-america-2017).

Let's discuss the problems after the contest.

Good luck to all the teams.

Update: Statements (thanks aajjbb).

Update 2: Live Ranking.

Update 3: The contest ended some hours ago, still no final ranking, if anyone gets it, share it please.

Update 4: Final Ranking, congratulations to the winners!!

Update 5: Solutions in Spanish

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By k790alex, history, 4 years ago, In English
 
 
 
 
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By k790alex, 5 years ago, In English

Hi,

As most users know, upsolving is very important to improve in programming contests, sometimes you tried to solve a problem without luck, while seeing the same problem after some time (days / months / years?) you may be able to solve it, this means you improved the required skills to succeed this problem.

I tried to find all my unsolved problems from Codeforces without luck, in PROBLEMSET there is a frame (Last unsolved) with the list of the last 15 problems tried but that's not enough.

I checked the Codeforces API to find a way to check all my unsolved problems without luck, so I wrote a crawler to find them all, the project is on github: https://github.com/AlexITC/upsolving/

This tool uses your login details and extract the unsolved problems from Codeforces Rounds and from the Gym.

I hope this can be helpful.

P.S: If someone knows how to retrieve this information using Codeforces API, let me know please.

P.S.2: There is an unknown reason why all tried problems from gym are not retrieved, I may fix it when I have the time.

UPDATE

My friend thnkndblv made a great tool similar to this one and you only need to type your handle, here is the app: http://codeforced.github.io/handle/

UPDATE 2

I finally retrieved the tool for TJU (after 7 months), you can find it here: https://github.com/AlexITC/upsolving/tree/master/tju

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By k790alex, history, 5 years ago, In English

Hi,

Since sometime ago while I read things about competitive programming I was storing the links to useful material (the one I think is good explained or hard to find), I'm collecting all the links and storing them in my blog, this may be useful for people trying to learn common (or not so common) things useful for programming contests.

The list is not in the best order, I may improve it some day, the list is being updated when I found an interesting post.

You can share links here and I may post it in the list.

http://halexv.blogspot.mx/2015/10/competitive-programming-resources.html

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By k790alex, 5 years ago, In English
 
 
 
 
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By k790alex, history, 6 years ago, In English
 
 
 
 
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By k790alex, history, 6 years ago, In English

Hi,

acm.tju.edu.cn has been down for more than a week, this is the longer time I had experienced with this, does someone knows if this is going to live again?

Thanks.

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Tags tju
 
 
 
 
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By k790alex, history, 6 years ago, In English

Hello,

I'm trying to improve my English (talking / listening), I would like to talk with native speakers.

We can talk about whatever you like, I will be online in skype most of the day in weekends and may a little time other days, add me to skype (k790alex) or send me a message if you like to help me, I would be glad if I can help you in something like Software Development, Computer Science or Algorithms and Data Structures (Why not?), anyone is welcome.

P.S: I tried online sites for this purpose but it was hard to get a talk with a person (at least in free versions).

P.S.2: Yes, I know Data Structures (Segment Tree, BIT, BST, etc).

Thanks.

UPDATE: Too many up votes but I only have one user to talk in weekends

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By k790alex, 6 years ago, In English

Hello, I'm trying to solve this problem (link).

A brief description:

Given two strings (s, t) and Q queries, each query contains an integer K, you should count how many substrings of s can be equal to t with changing exactly K characters of s.

constrains: |s| <= 10^6 |s| > |t| Q <= 10^5 characters can be 'x' or 'y' only

I got a solution using suffix tree which runs in linear time but my problem is that it uses too much memory.

I tried to reduce it to suffix array but I couldn't.

As the constrains are high I guess I need a linear time solution, can you see how to do it using less memory?

Thanks.

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By k790alex, 7 years ago, In English

Given an array where each element represents a stick length, how many triangles can be formed choosing 3 different elements?

I know O(N^2) solution, is there a faster solution for this problem?

Thanks.

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By k790alex, 7 years ago, In English

In my job, we launch a challenge for testing a security system we designed.

I know this is not a cryptography forum but here should be some cryptography fans (like me).

The statement is here: http://sac.mx/challenge.html

There are up to 200 dollars in prizes.

Thanks for reading.

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By k790alex, 7 years ago, In English

Hi, since sometime ago, I was trying to solve this problem.

I tried using brute force, suffix array and suffix tree, and I got TLE.

My approach is this:

  • Create a suffix tree for the text O(M)

  • Count how many times appear each pattern in the text O(N*S)

  • Find the answer O(N)

where:

M = text length

N = number of patterns

S = pattern length

Can some give me any hints?

Thanks.

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By k790alex, 7 years ago, In English

Problem:

Given a string S find the longest repeated substring non overlaps.

1 <= |S| <= 50,000

Input: ABBBB

output: BB

I'm trying to solve a problem like this, after thinking some time I came up with this solution using suffix array:

pos[i] -> sorted suffix array lcp[i] -> longest common prefix between i-th suffix and (i-1)-th suffix lcp2[i] -> like lcp but without overlaps -> lcp[i] = min(l p[i], abs( pos[i] — pos[i — 1] ) )

ans = max( lcp2[i] ) for 1 <= i < |S|

my approach was working for some cases but it fails for the test I wrote before.

I could think in a brute force solution which I think its some obvious:

For all repeated substring SUB, try all substring of SUB and test if have overlaps. 

Do you have a better way?

Thanks.

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By k790alex, 7 years ago, In English

I participated in this contest but I could'n be able to solve this task: 394B — Very Beautiful Number

I really want to know a method for solving it but like this contest was held in a black day (a day without data recovered) for codeforces, I couldn't find editorial.

I saw some accepted solutions but I would like to see a explication with more details.

I only could think in a solution using divisivility rules for 1 to 9 but I couldn't complete at all.

I think my idea have to many work for a div2 problem B, then if someone could explain me an easy solution, i would be grateful.

Thanks.

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By k790alex, 7 years ago, In English

Hi, I read this Topic and I was thinking about its applications in contest but I couldn't get any.

I only know that this algorithm is useful for cryptography but I worder how it could be used in contests.

If you could provide me an example I would be grateful and a problem would be useful too.

Thanks in advance.

UPDATE: thanks to all, i continue reading and I found this link, it is another application.

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By k790alex, 7 years ago, In English

This is the last contest before ICPC México and Latin America, 5 hours contest, dont forget to check the time.

http://coj.uci.cu/contest/contestview.xhtml?cid=1319

http://www.timeanddate.com/worldclock/fixedtime.html?day=5&month=11&year=2013&hour=12&min=30&sec=0&p1=99

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By k790alex, 7 years ago, In English

For those who are practicing for ICPC contest, I use to practice in COJ and it have real contest many times and fortunately many are public, this online judge is host of many latin contest (Cuba, México, Argentina, etc) and we could enter to practice, many of this contests are for preparing for ICPC contest, you are welcome to participate if you want, the problems are from latin problem setters. It would be good if we discuss the problems here affter contest.

P.S: This is a five hours contest with normal ICPC rules.

http://coj.uci.cu/contest/contestview.xhtml?cid=1318

It starts in 10 hours: http://www.timeanddate.com/worldclock/fixedtime.html?day=29&month=10&year=2013&hour=11&min=30&sec=0&p1=99

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By k790alex, 7 years ago, In English

For those who are practicing for ICPC contest, I use to practice in COJ and it have real contest many times and fortunately many are public, this online judge is host of many latin contest (Cuba, México, Argentina, etc) and we could enter to practice, many of this contests are for preparing for ICPC contest, you are welcome to participate if you want, the problems are from latin problem setters. It would be good if we discuss the problems here affter contest.

P.S: This is a five hours contest with normal ICPC rules.

http://coj.uci.cu/contest/contestview.xhtml?cid=1317

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By k790alex, 7 years ago, In English

Today i was in CF Round 207 when I receive a message from a user sending me the code used to solve a problem (I sent getting WA) and requesting me the solution for another problem.

I don't know how could be people trying to cheat in a contest when a it is for testing yoursefl about how good/bad are you.

My suggestion is to disable the talk system while a contest is running because with this experience I could realize that here we have users who only want to get a good ranking cheating and that's awful for me.

With talk system up you could only find users who solve a problem and request for an explication or worse, for a code.

Obviously I didn't sent any code but I don't know if another user would send it if someone request.

That's my opinion.

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By k790alex, 8 years ago, In English
 
 
 
 
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