Developers Club geek daily blog

International mathematical Olympic Games of school students 2015. May I? Would I like? Whether I will solve?

1 year, 11 months ago
I write article for that myself when was the school student.

On July 15 in Chiang-Ma'a (Thailand) the 56th International mathematical Olympic Games have come to the end. First place was won by the USA, the second? China, the third? South Korea, the fourth? North Korea, the fifth? Vietnam, the sixth? Australia, the seventh? Iran.

On the International mathematical Olympic Games each country is presented by no more than six school students. They have to solve six problems, for each of which it is possible to get at most seven points. Medals are received by about a half of participants, between them gold, silver and bronze awards are distributed in the ratio 1:2:3. The last time at these Olympic Games the Russian school students won first place in 2007.

There is opinion, what task 6? there was the most complex challenge for all history of the International mathematical Olympic Games which is held in 1959?.

Somebody will be able to solve though something?

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How to solve entrance examination in School of data analysis of Yandex

1 year, 11 months ago
Summer? time of entrance examinations. Right now selection in School of data analysis of Yandex comes to the end? there are interviews for those who has already passed examination. In ShAD teach machine learning, computer sight, the analysis of texts in natural language and other directions of modern Computer Science. Two years students study subjects which are not included usually into university programs though are in huge demand both in science, and in the industry. It is possible to study not only in Moscow? at School branches in Yekaterinburg, Minsk, Kiev, Novosibirsk, St. Petersburg are open. There is also correspondence department on which it is possible to be trained, watching video lectures and corresponding with teachers of the Moscow School by mail.

But to come to ShAD, it is necessary to pass three stages successfully? to fill in the questionnaire on the site, to pass entrance examination and to come to interview. Annually undergraduates, graduates and graduate students of MSU, MFTI, HSE, ITMO, St.Petersburg State University come to ShAD, URFA, NSU and not all of them cope with our tests. This year we have received questionnaires from 3500 people, 1000 from which has been allowed to examination, and only 350 have handed over it successfully.

For those who wants to try and understand, on what it is capable, we have prepared analysis of entrance examination of this year. With option which we have selected for you, 56% solving it have consulted. In this table you can see, how many people could solve each of tasks in it.
Task 1 2 3 4 5 6 7 8
Has solved 57% 68% 40% 35% 29% 12% 20% 6%

But for a start it would be desirable to explain that we check examination and as we approach its drawing up. In the very first years of existence of ShAD of written examination was not as requests was a little more, and with all who has passed online testing, it turned out to talk personally. But and interviews were more long; some graduates remember how talked to them till six hours, offering many complex challenges. Then arriving became more? and in 2012 there was written examination.

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2 Pi or not 2 Pi? here in what question

1 year, 11 months ago

Transfer of post of Giorgia Fortuna "2 Pi or Not 2 Pi?".
I express huge gratitude to Kirill Guzenko for the help in transfer.

Three months ago the world (or at least the world of geeks) celebrated day of Pi (03.14.15...). Today (6/28? On June 28, 2015) other mathematical day? day 2?, or put Tau (2? = 6.28319...).

Some say, what day to ta really is day for celebration, and what? (= 2?), but not?, has to be the most important constant. All has begun in 2001 with opening speech of the well-known essay of Bob Pale, the mathematician from university of Utah:

? I know, what some will consider it as blasphemy, but I consider, what?? it is error?.

It has caused in some circles celebration of day to ta? or, how many speak, the only day in which it is possible to eat two pi (horns) (2pies≈2?? word play in English language).

However whether truth what?? the constant is better? In the modern world it is quite simple to check it, and century day of number pi, very actively involved Wolfram Language). I have begun with consideration of 320000 pre-prints on to look, how many actually formulas contain 2? what contain simply? or? with other multiplicands.

Here the cloud from some formulas constructed by means of the WordCloud function, containing 2?:


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Algorithmic information theory and randomness of individual objects

1 year, 11 months ago
The concept of entropy in the middle of the XX century was entered by Claude Shannon. It can be described intuitively as "average number of bits of information in one value of random variable". But it cannot be applied to individual objects (we will tell, to the text of the novel or DNA) — where there is no ensemble of many homogeneous objects, there are no random variables also.

In the mid-sixties it became clear to different people (Kolmogorov, Solomonov, Levin, Cheytin) that it is possible to define amount of information (complexity) of individual object as the minimum length of the program which this object generates (at natural restrictions on programming language). There was algorithmic information theory which was connected with different areas: from philosophical questions of the bases of probability theory (when we reject statistical hypotheses?) to combination theory (the inequality connecting the sizes of sets and their projections) and computability theory.

Lecture which we have selected for you today, the famous mathematician Alexander Shen read at faculty of computer sciences of the Tower. Once he under the leadership of Vladimir Uspensky, the pupil Kolmogorov, has defended the dissertation "Algorithmic options of concept of entropy".

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Creation of effect of Droste in Wolfram Language (Mathematica)

1 year, 11 months ago

Transfer of a post of John Maklun of "Droste Effect with Mathematica". The code given in article can be downloaded at the end of a post.
I express huge gratitude to Kirill Guzenko for the help in transfer.

Droste's (wiki) effect represents recursive inclusion by the image most in itself. The name comes from the Droste cocoa powder which in 1904 was on sale in packaging on which the nurse who held a box on which there was a nurse, well and so on was represented. The simplest implementation — to scale and transform the image, and then to place it on the unmodified exact copy, then to start process over again. Look at demonstration in which it is used original illustrations of packaging Droste. However much more interesting results can be achieved if to use the function theory of complex variable (FTCV). Asher M. K. was the first who popularized idea of conformal mappings in relation to images, however by means of computers we can easily implement this idea in photos for obtaining something similar:

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Hardkorny oldskul: QEMU and reverse of image of floppik

1 year, 11 months ago

In anticipation of "confrontation" of NeoQUEST-2015 which will take place already tomorrow, on July 2 at 11:00, in St. Petersburg, we publish write-up of the last not sorted online-stage task!

We remind that input on action free, and we wait for all who is interested in information security! NeoQUEST — is chance to learn something new, to improve the "hacker" skills, to communicate to colleagues, to observe decisive competition of the best hackers, and simply perfectly to spend time!

In more detail about venue and subjects of reports of NeoQUEST-2015 it is possible to read here and there.

The online-stage task left "for dessert" was rather oldskulny: there is enough already of that was talked of dump all of the forgotten floppy disk long ago! How participants of quest had to tinker with reverse and with QEMU — under cat!

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Use of monads in With ++. Part 2: status monad

1 year, 12 months ago
Part 1
Part 2

What will you make if tomorrow win in lottery? Buy sports car, will give up work and will go to tour across the USA? And can be will become the founder of home company, will increase status and buy the personal airplane?

All of us like to do plans, and most often they lean on our financial status. Such plans can be described by function. For example, plan of purchase of a car it:

pair<Car, Cash> buyCar(Cash cashIn)

On input at us quantity of money (Cash), and on output the brand new machine (Car) and some quantity (not the fact that the positive!) the remained finance (Cash). Generally, the financial plan — is function which accepts money and returns result, plus the remained quantity of money. It can be described by template:

template<class A>
using Plan = function<pair<A, Cash>(Cash)>;

You can integrate small plans to receive the big. For example, you can start up the funds for the trip which have remained after purchase of a car or invest in business. If you have things already belonging to you, they can become part of your plans:

template<class A>
Plan<A> got_it(A a)
    return [a](Cash s) { return make_pair(a, s); };

What relation all these dreams have to solution of our puzzle? Earlier I said that we need to save somewhere status, and it is way as which programmers in functional languages work with status. Instead of explicit modifying of status they write code which generates the plan of action.

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Use of monads in With ++. Part 1: list monad

2 years ago
Part 1
Part 2

Sometimes programmers on With ++ ask to give example of task which cannot be solved without use of monads. Let's begin with that this question is incorrect in itself — it all the same what to ask, whether there is task which cannot be solved without cycles. It is obvious if in your language there is support of the operator goto, you can do without use of iteration statements. That monads (and cycles) can make for you, it to simplify your code and better to help to structure it. As use of cycles turns spaghetti code in normal, and use of monads can turn your code in imperative style into the declarative. This transformation can easier help to write, understand, support and expand your code.

Well and here to you problem which can get on interview. It is not absolutely trivial, some approaches to solution and the best of them are possible not at once are obvious — just over what it is worth thinking.
The following puzzle is offered to you:

  s e n d
+ m o r e
m o n e y

Each letter corresponds to digit from 0 to 9. It is necessary to write the program which will pick up such compliances that the written addition operation was correct. Before continuing reading article — think minute, as if you have solved this problem?

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Exclusively simple tasks of AppSec .NET

2 years ago
I suggest all to warm up brain after days off and to begin working week with simple, at first sight, problems on programming on C#. Perhaps these tasks will force you to look at code of the projects from the new party as all of them concern gloomy area – area of safety of applications, at Application Security. About AppSec and the .NET platform write not much, speak even less, some in general consider that use of any managed of language, does magic image application protected. I try to rectify this situation, telling at conferences about different aspects of safety of .NET of platform. So on this week, on Thursday, our community SPB .NET Community carries out mitap in St. Petersburg completely devoted to questions of development of the protected ASP .NET of applications. To whom details of this meeting who wants to learn more about community .NET of developers of St. Petersburg are interesting and to try the hand in solution of tasks of AppSec. NET, I invite under kat!

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Masons select the sun: cracking of the program for Sun Solaris &SPARC in the NeoQUEST-2015 task

2 years ago
Leaving from usual x86 of architecture — it is always interesting, and in the NeoQUEST-2015 "Masons Select the Sun" task it was offered to participants to crack the program which is developed and written for Sun Solaris 2.6 versions of the 1995th year moreover and for architecture of SPARC!

The task was difficult not only for passing — its preparation also took some time. Under a cat:
  • Councils for the Solaris installation: how to make it, having minimized labor costs?
  • Start of Solaris 2.6 under qemu for Windows 8.1
  • Detailed analysis of two methods of passing of a task

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