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  • How to Check Authenticity of an AJAX Request

    - by Alex Reisner
    I am designing a web site in which users solve puzzles as quickly as they can. JavaScript is used to time each puzzle, and the number of milliseconds is sent to the server via AJAX when the puzzle is completed. How can I ensure that the time received by the server was not forged by the user? I don't think a session-based authenticity token (the kind used for forms in Rails) is sufficient because I need to authenticate the source of a value, not just the legitimacy of the request. Is there a way to cryptographically sign the request? I can't think of anything that couldn't be duplicated by a hacker. Is any JavaScript, by its exposed, client-side nature, subject to tampering? Am I going to have to use something that gets compiled, like Flash? (Yikes.) Or is there some way to hide a secret key? Or something else I haven't thought of? Update: To clarify, I don't want to penalize people with slow network connections (and network speed should be considered inconsistent), so the timing needs to be 100% client-side (the timer starts only when we know the user can see the puzzle). Also, there is money involved so no amount of "trusting the user" is acceptable.

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  • What is the cost of memory access?

    - by Jurily
    We like to think that a memory access is fast and constant, but on modern architectures/OSes, that's not necessarily true. Consider the following C code: int i = 34; int *p = &i; // do something that may or may not involve i and p {...} // 3 days later: *p = 643; What is the estimated cost of this last assignment in CPU instructions, if i is in L1 cache, i is in L2 cache, i is in L3 cache, i is in RAM proper, i is paged out to an SSD disk, i is paged out to a traditional disk? Where else can i be? Of course the numbers are not absolute, but I'm only interested in orders of magnitude. I tried searching the webs, but Google did not bless me this time.

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  • Solving problems with near infinite potential solutions

    - by Zonda333
    Today I read the following problem: Use the digits 2, 0, 1, 1 and the operations +, -, x, ÷, sqrt, ^ , !, (), combinations, and permutations to write equations for the counting numbers 1 through 100. All four digits must be used in each expression. Only the digits 2, 0, 1, 1 may be used, and each must be used exactly once. Decimals may be used, as in .1, .02, etc. Digits may be combined; numbers such as 20 or 101 may be used. Example: 60 = 10*(2+1)!, 54 = ¹¹C2 - 0! Though I was able to quickly find around 50 solutions quite easily in my head, I thought programming it would be a far superior solution. However, I then realized I had no clue how to go about solving a problem like this. I am not asking for complete code for me to copy and paste, but for ideas about how I would solve this problems, and others like it that have nearly infinite potential solutions. As I will be writing it in python, where I have the most experience, I would prefer if the answers were more python based, but general ideas are great too.

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  • Stop overlooking minor details

    - by Mark Lubin
    Compared to most people on this site I am admittedly a novice. I wanted to get some advice from the pros on how to avoid making stupid errors in your code. Is there anyone else who had the problem when they were first starting out of missing some detail that causes big problems? Are there any habits or behaviors that helped you over come this.

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  • Optimizing Code

    - by Claudiu
    You are given a heap of code in your favorite language which combines to form a rather complicated application. It runs rather slowly, and your boss has asked you to optimize it. What are the steps you follow to most efficiently optimize the code? What strategies have you found to be unsuccessful when optimizing code? Re-writes: At what point do you decide to stop optimizing and say "This is as fast as it'll get without a complete re-write." In what cases would you advocate a simple complete re-write anyway? How would you go about designing it?

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  • Graph search problem with route restrictions

    - by Darcara
    I want to calculate the most profitable route and I think this is a type of traveling salesman problem. I have a set of nodes that I can visit and a function to calculate cost for traveling between nodes and points for reaching the nodes. The goal is to reach a fixed known score while minimizing the cost. This cost and rewards are not fixed and depend on the nodes visited before. The starting node is fixed. There are some restrictions on how nodes can be visited. Some simplified examples include: Node B can only be visited after A After node C has been visited, D or E can be visited. Visiting at least one is required, visiting both is permissible. Z can only be visited after at least 5 other nodes have been visited Once 50 nodes have been visited, the nodes A-M will no longer reward points Certain nodes can (and probably must) be visited multiple times Currently I can think of only two ways to solve this: a) Genetic Algorithms, with the fitness function calculating the cost/benefit of the generated route b) Dijkstra search through the graph, since the starting node is fixed, although the large number of nodes will probably make that not feasible memory wise. Are there any other ways to determine the best route through the graph? It doesn't need to be perfect, an approximated path is perfectly fine, as long as it's error acceptable. Would TSP-solvers be an option here?

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  • Are There Any Other Web Programming Languages That Can Be Used Without A Framework Aside From PHP?

    - by Ygam
    Python needs a framework, so does Java (for the web). I don't know much about Ruby or Coldfusion. But is there another language out there for the web that can stand alone as it is without a need for a framework or without strict adherence to a design pattern (MVC and the likes) aside from PHP? BTW, the statement that Python and Java needs a framework to work with the web came purely from my readings on articles and books; I might be mistaken.

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  • Creating our own APIs

    - by Markii
    We need a bunch of APIs for our service and are looking at the job as being quite tedious for starting from scratch because we need strict user restrictions such as max queries and usage statistics. Are there any pre-made services or scripts for this already?

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  • Word filter that groups words?

    - by Legend
    Is there any library that achieves the following: Convert Microsoft Windows 98 Microsoft Windows XP Windows 7 Windows Ultimate Desktop Windows to Windows 4 The complicated part here is to recognize that "Desktop Windows" is an anomaly here and not count it. If nothing is added before the word "Windows", perhaps it can be counted but if there is something else and the suffix does not match any popular suffix, it can still be counted. Maybe I am a little vague here but perhaps someone could have an idea about what I am talking about here. Any suggestions?

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  • What is going to be "the next Hype" ? [closed]

    - by kabado
    I know it's a very vague question, but maybe the answers could act like a poll about what could possibly be the next big event in computer science. A new language ? A new technology ? A new architecture ? A new business model ? Please provide details, what is it and why do you think it's going to rule the world.

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  • When did you feel comfortable with programming?

    - by misterwebz
    I've been programming for about 6 months, but i still feel like i haven't learned anything. Or maybe i'm overwhelmed by the things i still don't know. Am i doing something wrong here or is this normal? I want to be able to work as a freelancer in a year or two, but i'm not sure if that goal is achievable. So when did you feel comfortable using your programming language of choice and how did you learn it?

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  • A StringToken Parser which gives Google Search style "Did you mean:" Suggestions

    - by _ande_turner_
    Seeking a method to: Take whitespace separated tokens in a String; return a suggested Word ie: Google Search can take "fonetic wrd nterpreterr", and atop of the result page it shows "Did you mean: phonetic word interpreter" A solution in any of the C* languages or Java would be preferred. Are there any existing Open Libraries which perform such functionality? Or is there a way to Utilise a Google API to request a suggested word?

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  • Arrange 0's & 1's in a array

    - by Ganesh M
    This is one of an interview question which I had recently. I would like to know others perception of approach for this problem. Question: You are given a structure which holds an employee details with two elements as int Deptartment and string Name. struct Employee { string Name; int Dept; } You are given details of N Employees among which there are N/2 employees Dept are 0's and N/2 employees dept are 1's arranged in some random order. You need to sort the employee details based on their Dept value and it should be stable i.e., the order of 1s and 0s in the original record should be maintained. For example, given the following sample data: Name Dept X1 0 X2 1 X3 0 X4 1 X5 0 after sorting the result should be: Name Dept X2 1 X4 1 X1 0 X3 0 X5 0 The algorithm should be stable and the complexity should be o(N), with constant space for additional variables (which means sorting should be done in-place).

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  • Creative Technical Interview Questions for Developers

    - by John Shedletsky
    I do a good number of in-person technical interviews for new developers. I like to ask technical questions where I ask people to either code something up or develop an algorithm to solve a task. I feel my current repertoire is uninspired. In my opinion, the ideal interview question has these qualities: Multiple solutions, where some are obviously better than others, and some that involve subtle trade-offs (discussing tradeoffs is a good way to gauge someone's experience, in my opinion). Novelty - asking the "insert this element into a linked list" question is only good for weeding out people who never did their homework. Elegant - I like questions where the core problem isn't hidden in a lot of details. Everyone should be able to understand the problem, even if everyone can't solve it on the whiteboard. Elegant questions are difficult without involving undue amounts of "domain knowledge" or getting too narrow. Have you been on either side of an interview where someone (maybe you!) asked a particularly good programming or algorithms question?

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  • Code Golf: Connecting the dots

    - by ChristopheD
    Description: The input are multiple lines (terminated by a newline) which describe a 'field'. There are 'numbers' scattered across this field: the numbers always start at 1 they follow the ordering of the natural numbers: every 'next number' is incremented with 1 every number is surrounded by (at least) one whitespace on it's left and right Task: Draw lines between these numbers in their natural order (1 -> 2 -> 3 -> ...N) with the following characteristics: replace a number with a '+' character for horizontal lines: use '-' for vertical lines: use '|' going left and down or right and up: / going left and up or right and down: \ Important note: When drawing lines of type 4 and 5 you can assume that : (given points to connect with coordinates x1, y1 and x2, y2) distance(x1,x2) == distance(y1,y2). Have a look at the examples to see where you should 'attach' the lines. It is important to follow the order in which the dots are connected (newer lines can be drawn over older lines). Sample input 1 9 10 8 7 6 5 11 13 12 3 4 14 15 16 1 2 Sample output 1 /+ / | / | +/ +--+ | +\ | \ | \+ /+ | / | /+-------------+/ +---+ / | +--+ | + | +--------------------------+ Sample input 2 4 2 3 5 6 1 8 7 Sample output 2 /+ / | / | / | /+------------------+/ +--------+\ / \ +/ +--------------------------------------+ Winner: shortest solution (by code count). Input can be read via command line.

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  • guarantee child records either in one table or another, but not both?

    - by user151841
    I have a table with two child tables. For each record in the parent table, I want one and only one record in one of the child tables -- not one in each, not none. How to I define that? Here's the backstory. Feel free to criticize this implementation, but please answer the question above, because this isn't the only time I've encountered it: I have a database that holds data pertaining to user surveys. It was originally designed with one authentication method for starting a survey. Since then, requirements have changed, and now there are two different ways someone could sign on to start a survey. Originally I captured the authentication token in a column in the survey table. Since requirements changed, there are three other bits of data that I want to capture in authentication. So for each record in the survey table, I'm either going to have one token, or a set of three. All four of these are of different types, so my thought was, instead of having four columns where either one is going to be null, or three are going to be null ( or even worse, a bad mashup of either of those scenarios ), I would have two child tables, one for holding the single authentication token, the other for holding the three. Problem is, I don't know offhand how to define that in DDL. I'm using MySQL, so maybe there's a feature that MySQL doesn't implement that lets me do this.

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  • Starting a personal reuasable code repository.

    - by Rob Stevenson-Leggett
    Hi, I've been meaning to start a library of reusable code snippets for a while and never seem to get round to it. At the moment I just tend to have some transient classes/files that I drag out of old projects. I think my main problems are: Where to start. What structure should my repository take? Should it be a compiled library (where appropriate) or just classes/files I can drop into any project? Or a library project that can be included? What are the licencing implications of that? In my experience, a built/minified library will quickly become out of date and the source will get lost. So I'm leaning towards source that I can export from SVN and include in any project. Intellectual property. I am employeed, so a lot of the code I write is not my IP. How can I ensure that I don't give my own IP away using it on projects in work and at home? I'm thinking the best way would be to licence my library with an open source licence and make sure I only add to it in my own time using my own equipment and therefore making sure that if I use it in a work project the same rules apply as if I was using a third party library. I write in many different languages and often would require two or more parts of this library. Should I look at implementing a few template projects and a core project for each of my chosen reusable components and languages? Has anyone else got this sort of library and how do you organise and update it?

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  • Is 1 for TRUE or FALSE ?

    - by CharlesChipy
    I always forget :S How do you remember which number stands for TRUE or FALSE? (when I started css the colors black and white always confused me. Is white #FFFFFF or #000000. A trick I came up with: black is 0,because z0rr0 is dressed in …)

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  • What is a Custom Class?

    - by John Saunders
    Many questions here on SO ask about custom classes. I, on the other hand, have no idea what they're talking about. "Custom class" seems to mean the same thing I mean when I say "class". What did I miss, back in the '80s, that keeps me from understanding? I know that it's possible to purchase a packaged system - for Accounting, ERP, or something like that. You can then customize it, or add "custom code" to make the package do things that are specific to your business. But that doesn't describe the process used in writing a .NET program. In this case, the entire purpose of the .NET Framework is to allow us to write our own code. There is nothing useful out of the box.

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  • Database Optimization techniques for amateurs.

    - by Zombies
    Can we get a list of basic optimization techniques going (anything from modeling to querying, creating indexes, views to query optimization). It would be nice to have a list of these, one technique per answer. As a hobbyist I would find this to be very useful, thanks. And for the sake of not being too vague, let's say we are using a maintstream DB such as MySQL or Oracle, and that the DB will contain 500,000-1m or so records across ~10 tables, some with foreign key contraints, all using the most typical storage engines (eg: InnoDB for MySQL). And of course, the basics such as PKs are defined as well as FK contraints.

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  • Shortest distance between points on a toroidally wrapped (x- and y- wrapping) map?

    - by mstksg
    I have a toroidal-ish Euclidean-ish map. That is the surface is a flat, Euclidean rectangle, but when a point moves to the right boundary, it will appear at the left boundary (at the same y value), given by x_new = x_old % width Basically, points are plotted based on: (x_new, y_new) = ( x_old % width, y_old % height) Think Pac Man -- walking off one edge of the screen will make you appear on the opposite edge. What's the best way to calculate the shortest distance between two points? The typical implementation suggests a large distance for points on opposite corners of the map, when in reality, the real wrapped distance is very close. The best way I can think of is calculating Classical Delta X and Wrapped Delta X, and Classical Delta Y and Wrapped Delta Y, and using the lower of each pair in the Sqrt(x^2+y^2) distance formula. But that would involve many checks, calculations, operations -- some that I feel might be unnecessary. Is there a better way?

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