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  • Rot13 for numbers.

    - by dreeves
    EDIT: Now a Major Motion Blog Post at http://messymatters.com/sealedbids The idea of rot13 is to obscure text, for example to prevent spoilers. It's not meant to be cryptographically secure but to simply make sure that only people who are sure they want to read it will read it. I'd like to do something similar for numbers, for an application involving sealed bids. Roughly I want to send someone my number and trust them to pick their own number, uninfluenced by mine, but then they should be able to reveal mine (purely client-side) when they're ready. They should not require further input from me or any third party. (Added: Note the assumption that the recipient is being trusted not to cheat.) It's not as simple as rot13 because certain numbers, like 1 and 2, will recur often enough that you might remember that, say, 34.2 is really 1. Here's what I'm looking for specifically: A function seal() that maps a real number to a real number (or a string). It should not be deterministic -- seal(7) should not map to the same thing every time. But the corresponding function unseal() should be deterministic -- unseal(seal(x)) should equal x for all x. I don't want seal or unseal to call any webservices or even get the system time (because I don't want to assume synchronized clocks). (Added: It's fine to assume that all bids will be less than some maximum, known to everyone, say a million.) Sanity check: > seal(7) 482.2382 # some random-seeming number or string. > seal(7) 71.9217 # a completely different random-seeming number or string. > unseal(seal(7)) 7 # we always recover the original number by unsealing.

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  • How is dynamic memory allocation handled when extreme reliability is required?

    - by sharptooth
    Looks like dynamic memory allocation without garbage collection is a way to disaster. Dangling pointers there, memory leaks here. Very easy to plant an error that is sometimes hard to find and that has severe consequences. How are these problems addressed when mission-critical programs are written? I mean if I write a program that controls a spaceship like Voyager 1 that has to run for years and leave a smallest leak that leak can accumulate and halt the program sooner or later and when that happens it translates into epic fail. How is dynamic memory allocation handled when a program needs to be extremely reliable?

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  • Is Polyglot programming important?

    - by Kb
    Trying to learn more about Polyglot programming. What is it exactly and is it important? Look like it is cross platform coding and interoperability across platforms... I found this article by Ted Neward (Thoughtworks) interesting.

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  • UK Postcode search

    - by Imran
    I want to build a website where you can search by entering the postcode (UK). I know that RoyalMail owns the Database to do this (it's only very expensive, $100K). What are my options?

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  • Is there an equivalent in Scala to Python's more general map function?

    - by wheaties
    I know that Scala's Lists have a map implementation with signature (f: (A) => B):List[B] and a foreach implementation with signature (f: (A) => Unit):Unit but I'm looking for something that accepts multiple iterables the same way that the Python map accepts multiple iterables. I'm looking for something with a signature of (f: (A,B) => C, Iterable[A], Iterable[B] ):Iterable[C] or equivalent. Is there a library where this exists or a comparable way of doing similar?

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  • Code Golf: Morse code

    - by LiraNuna
    The challenge The shortest code by character count, that will input a string using only alphabetical characters (upper and lower case), numbers, commas, periods and question mark, and returns a representation of the string in Morse code. The Morse code output should consist of a dash (-, ascii 0x2D) for a long beep (aka 'dah') and a dot (., ascii 0x2E) for short beep (aka 'dit'). Each letter should be separated by a space (' ', ascii 0x20), and each word should be separated by a forward slash (/, ascii 0x2F). Morse code table: Test cases: Input: Hello world Output: .... . .-.. .-.. --- / .-- --- .-. .-.. -.. Input: Hello, Stackoverflow. Output: .... . .-.. .-.. --- --..-- / ... - .- -.-. -.- --- ...- . .-. ..-. .-.. --- .-- .-.-.- Code count includes input/output (i.e full program).

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  • Word Jumble Algorithm

    - by MasterMax1313
    Given a word jumble (i.e. ofbaor), what would be an approach to unscramble the letters to create a real word (i.e. foobar)? I could see this having a couple of approaches, and I think I know how I'd do it in .NET, but I curious to see what some other solutions look like (always happy to see if my solution is optimal or not). This isn't homework or anything like that, I just saw a word jumble in the local comics section of the paper (yes, good ol' fashioned newsprint), and the engineer in me started thinking.

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  • Derivative of a Higher-Order Function

    - by Claudiu
    This is in the context of Automatic Differentiation - what would such a system do with a function like map, or filter - or even one of the SKI Combinators? Example: I have the following function: def func(x): return sum(map(lambda a: a**x, range(20))) What would its derivative be? What will an AD system yield as a result? (This function is well-defined on real-number inputs).

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  • data structure algorithms for database searching

    - by Ygam
    I was used to the traditional way of doing database searching with the following using wildcards for term searches using where clause for specific data like addresses and names but at other times, I found these common methods to produce code that is so bloated, especially when it comes to complex searches. Are there algorithms out there that you use for complex database searching? I tried to look for some but had a hard time doing so. I stumbled accross the binary search but I can't find a use for it :(

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  • Why scala not allowing '$' identifier in case statement?

    - by Alex R
    this works as expected scala 3 match { case x:Int = 2*x } res1: Int = 6 why does this fail? scala 3 match { case $x:Int = 2*$x } :1: error: '=' expected but ':' found. 3 match { case $x:Int = 2*$x } ^ scala 3 match { case `$x`:Int = 2*$x } :1: error: '=' expected but ':' found. 3 match { case `$x`:Int = 2*$x } ^ scala 3 match { case `$x` : Int = 2*$x } :1: error: '=' expected but ':' found. 3 match { case `$x` : Int = 2*$x } '$' is supposed to be a valid identifier character, as demonstrated here: scala var y = 1 y: Int = 1 scala var $y = 2 $y: Int = 2 Thanks

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  • Storing date and time as epoch vs native datetime format in the database

    - by zakovyrya
    For most of my tasks I find it much easier to work with date and time in the epoch format: it's trivial to calculate timespan or determine if some event happened before or after another, I don't have to deal with time-zone issues if the data comes from different geographical sources, in case of scripting languages what I usually get from database when I request a datetime-typed column is a string that I need to parse in order to work with it. This list can go on, but for me in order to keep my code portable that's enough to ditch database's native datetime format and store date and time as integer. What do you guys think?

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  • Am I immoral for using a variable name that differs from its type only by case?

    - by Jason Baker
    For instance, take this piece of code: var person = new Person(); or for you Pythonistas: person = Person() I'm told constantly how bad this is, but have yet to see an example of the immorality of these two lines of code. To me, person is a Person and trying to give it another name is a waste of time. I suppose in the days before syntax highlighting, this would have been a big deal. But these days, it's pretty easy to tell a type name apart from a variable name. Heck, it's even easy to see the difference here on SO. Or is there something I'm missing? If so, it would be helpful if you could provide an example of code that causes problems.

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  • Generate colors between red and green for a power meter?

    - by Simucal
    I'm writing a java game and I want to implement a power meter for how hard you are going to shoot something. I need to write a function that takes a int between 0 - 100, and based on how high that number is, it will return a color between Green (0 on the power scale) and Red (100 on the power scale). Similar to how volume controls work: What operation do I need to do on the Red, Green, and Blue components of a color to generate the colors between Green and Red? So, I could run say, getColor(80) and it will return an orangish color (its values in R, G, B) or getColor(10) which will return a more Green/Yellow rgb value. I know I need to increase components of the R, G, B values for a new color, but I don't know specifically what goes up or down as the colors shift from Green-Red. Progress: I ended up using HSV/HSB color space because I liked the gradiant better (no dark browns in the middle). The function I used was (in java): public Color getColor(double power) { double H = power * 0.4; // Hue (note 0.4 = Green, see huge chart below) double S = 0.9; // Saturation double B = 0.9; // Brightness return Color.getHSBColor((float)H, (float)S, (float)B); } Where "power" is a number between 0.0 and 1.0. 0.0 will return a bright red, 1.0 will return a bright green. Java Hue Chart: Thanks everyone for helping me with this!

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  • What should every developer know about databases?

    - by Aaronaught
    Whether we like it or not, many if not most of us developers either regularly work with databases or may have to work with one someday. And considering the amount of misuse and abuse in the wild, and the volume of database-related questions that come up every day, it's fair to say that there are certain concepts that developers should know - even if they don't design or work with databases today. So: What are the important concepts that developers and other software professionals ought to know about databases? Guidelines for Responses: Keep your list short. One concept per answer is best. Be specific. "Data modelling" may be an important skill, but what does that mean precisely? Explain your rationale. Why is your concept important? Don't just say "use indexes." Don't fall into "best practices." Convince your audience to go learn more. Upvote answers you agree with. Read other people's answers first. One high-ranked answer is a more effective statement than two low-ranked ones. If you have more to add, either add a comment or reference the original. Don't downvote something just because it doesn't apply to you personally. We all work in different domains. The objective here is to provide direction for database novices to gain a well-founded, well-rounded understanding of database design and database-driven development, not to compete for the title of most-important.

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  • Which languages support *recursive* function literals / anonymous functions?

    - by Hugh Allen
    It seems quite a few mainstream languages support function literals these days. They are also called anonymous functions, but I don't care if they have a name. The important thing is that a function literal is an expression which yields a function which hasn't already been defined elsewhere, so for example in C, &printf doesn't count. EDIT to add: if you have a genuine function literal expression <exp>, you should be able to pass it to a function f(<exp>) or immediately apply it to an argument, ie. <exp>(5). I'm curious which languages let you write function literals which are recursive. Wikipedia's "anonymous recursion" article doesn't give any programming examples. Let's use the recursive factorial function as the example. Here are the ones I know: JavaScript / ECMAScript can do it with callee: function(n){if (n<2) {return 1;} else {return n * arguments.callee(n-1);}} it's easy in languages with letrec, eg Haskell (which calls it let): let fac x = if x<2 then 1 else fac (x-1) * x in fac and there are equivalents in Lisp and Scheme. Note that the binding of fac is local to the expression, so the whole expression is in fact an anonymous function. Are there any others?

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