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  • codingBat last2 using regex

    - by polygenelubricants
    Okay guys, this is similar to my repeatEnd and wordEnds efforts; I want to solve this codingBat Warmup-2 question using only regex-based techniques as a "brain gymnastics" exercise. This solution works for codingBat tests: public int last2(String str) { return str.isEmpty() ? 0 : str.split( str.replaceAll( ".*(.)(.)", "$1(?=$2)" //.replaceAll("(\\$.)", "\\\\\\\\Q$1\\\\\\\\E") ), -1 ).length - 1 - 1; } The monstrous octo-slashes aren't needed to pass codingBat, but is needed for a proper regex-based solution. That is, if I want this (and I do!): assert last2("..+++...++") == 2; I'd have to uncomment the second .replaceAll. I'm just wondering if others can come up with a simpler, more elegant regex solution for this problem. Preferably one that doesn't contain octo-slashes.

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  • Tail-recursive pow() algorithm with memoization?

    - by Dan
    I'm looking for an algorithm to compute pow() that's tail-recursive and uses memoization to speed up repeated calculations. Performance isn't an issue; this is mostly an intellectual exercise - I spent a train ride coming up with all the different pow() implementations I could, but was unable to come up with one that I was happy with that had these two properties. My best shot was the following: def calc_tailrec_mem(base, exp, cache_line={}, acc=1, ctr=0): if exp == 0: return 1 elif exp == 1: return acc * base elif exp in cache_line: val = acc * cache_line[exp] cache_line[exp + ctr] = val return val else: cache_line[ctr] = acc return calc_tailrec_mem(base, exp-1, cache_line, acc * base, ctr + 1) It works, but it doesn't memorize the results of all calculations - only those with exponents 1..exp/2 and exp.

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  • A way to measure performance

    - by Andrei Ciobanu
    Given Exercise 14 from 99 Haskell Problems: (*) Duplicate the elements of a list. Eg.: *Main> dupli''' [1..10] [1,1,2,2,3,3,4,4,5,5,6,6,7,7,8,8,9,9,10,10] I've implemented 4 solutions: {-- my first attempt --} dupli :: [a] -> [a] dupli [] = [] dupli (x:xs) = replicate 2 x ++ dupli xs {-- using concatMap and replicate --} dupli' :: [a] -> [a] dupli' xs = concatMap (replicate 2) xs {-- usign foldl --} dupli'' :: [a] -> [a] dupli'' xs = foldl (\acc x -> acc ++ [x,x]) [] xs {-- using foldl 2 --} dupli''' :: [a] -> [a] dupli''' xs = reverse $ foldl (\acc x -> x:x:acc) [] xs Still, I don't know how to really measure performance . So what's the recommended function (from the above list) in terms of performance . Any suggestions ?

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  • Differentiating Between UITouch Objects On The iPhone

    - by Jasarien
    Hey guys, I'm trying to differentiate between two (or more) UITouch objects on the iPhone. Specifically, I'd like to know the order in which the touches occurred. For instance, in my -touchesBegan:withEvent: method I get an NSSet of UITouch objects. Now I can find out how many touches there are, but, which object represents which finger? I notice the timestamp property on UITouch - is this what I'm looking for? I see how that would be useful to obtaining the last or first touch - providing the touches don't mutate... Therein lies my problem. I can use the timestamp to single out the latest touch, but then the touch that occurred first moves, and IT becomes the latest touch... At the end of this exercise, I'd like to be able to implement the "pinch" gesture to zoom in or out, etc. Any help would be greatly appreciated, thanks.

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  • Changing POST data used by Apache Bench per iteration

    - by Alabaster Codify
    I'm using ab to do some load testing, and it's important that the supplied querystring (or POST) parameters change between requests. I.e. I need to make requests to URLs like: http://127.0.0.1:9080/meth?param=0 http://127.0.0.1:9080/meth?param=1 http://127.0.0.1:9080/meth?param=2 ... to properly exercise the application. ab seems to only read the supplied POST data file once, at startup, so changing its content during the test run is not an option. Any suggestions?

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  • Proving that a function f(n) belongs to a Big-Theta(g(n))

    - by PLS
    Its a exercise that ask to indicate the class Big-Theta(g(n)) the functions belongs to and to prove the assertion. In this case f(n) = (n^2+1)^10 By definition f(n) E Big-Theta(g(n)) <= c1*g(n) < f(n) < c2*g(n), where c1 and c2 are two constants. I know that for this specific f(n) the Big-Theta is g(n^20) but I don't know who to prove it properly. I guess I need to manipulate this inequality but I don't know how

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  • How to create Shared VB Array Initialisors for NerdDinner

    - by David A Gibson
    Hello, I am trying to work my way through the NerdDinner tutorial - and as an exercise I'm converting it to VB as I go. I'm not very far in and after having gotten past the C# Yield statement I'm stuck on Shared VB Array Initialisors. static IDictionary<string, Regex> countryRegex = new Dictionary<string, Regex>() { { "USA", new Regex("^[2-9]\\d{2}-\\d{3}-\\d{4}$")}, { "UK", new Regex("(^1300\\d{6}$)|(^1800|1900|1902\\d{6}$)|(^0[2|3|7|8]{1}[0- 9]{8}$)|(^13\\d{4}$)|(^04\\d{2,3}\\d{6}$)")}, { "Netherlands", new Regex("(^\\+[0-9]{2}|^\\+[0- 9]{2}\\(0\\)|^\\(\\+[0-9]{2}\\)\\(0\\)|^00[0-9]{2}|^0)([0-9]{9}$|[0-9\\- \\s]{10}$)")}, Can anyone please help me write this in VB? Public Shared countryRegex As IDictionary(Of String, Regex) = New Dictionary(Of String, Regex)() {("USA", New Regex("^[2-9]\\d{2}-\\d{3}-\\d{4}$"))} This code has an error as it does not accept the String and the Regex as an item for the array. Thanks

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  • Database Instance

    - by Sam
    I read a statement from an exercise: construct a database instance which conforms to diagram 1 but not to diagram 2. The diagrams are different n-ary relationships that have different relationships. Diagram 1 has a many to one to many to one relationship. Diagram 2 has many to many to many to one relationship. So, to really understand this problem, what does a database instance mean? Is it to make an example or abstract entities like a1, a2, or a3. Thanks for your time.

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  • Dice face value recognition

    - by Jakob Gade
    I’m trying to build a simple application that will recognize the values of two 6-sided dice. I’m looking for some general pointers, or maybe even an open source project. The two dice will be black and white, with white and black pips respectively. Their distance to the camera will always be the same, but their position on the playing surface will be random. (not the best example, the surface will be a different color and the shadows will be gone) I have no prior experience with developing this kind of recognition software, but I would assume the trick is to first isolate the faces by searching for the square profile with a dominating white or black color (the rest of the image, i.e. the table/playing surface, will in distinctly different colors), and then isolate the pips for the count. Shadows will be eliminated by top down lighting. I’m hoping the described scenario is so simple (read: common) it may even be used as an “introductory exercise” for developers working on OCR technologies or similar computer vision challenges.

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  • Microsoft BizTalk Server vNext (after 2009 R2) - Feature Request

    - by Saravana Kumar
    All, This post is not a question; it’s more of asking for feed back and future request. The product team is always looking for feed back to facilitate the future direction of the product. Some of us as BizTalk Server MVP’s/partners get that privilege to work with the product team closely to give our feedback regularly based on our real world experience. But I believe there is a much wider BizTalk community out there working on closed door project that tests the strength of the product to extreme levels. I would like those passionate people to come forward and put their feature request. Let’s use the power of StackOverflow to help us here. We can vote up and down on each feature request, and see what's going to top the chart. I hope this will be a useful exercise. Updated 24th Feb: If you got more than one request, please post it as separate answers. So, its easy to vote against them.

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  • database design question

    - by Leonardo
    Hi all, I am building a database as a simple exercise, it could be hosted on any database server, so I am trying to keep things as much standard as possible. Basically what I would like to do is a 'code' table that get referenced by other entities. I explain: xcode id code r role p property code r admin r staff p title .... then I would like to have some view like: role (select * from code where xcode='r') r admin r staff property (select * from code where xcode='p') p title then, suppose we have an entity myentity id - 1 role - admin (foreign key to role) title - title (foreign key to property) Obviously I cannot create foreign key to a view, but this is to tell the idea I have in mind. How can I reflect such behaviour using whenever possible, standard sql syntax, then as a second option, database additional features like trigger ecc... ? Because if I tell that role and title in myentity are foreign key to 'code', instead of the views, nothing would stop me to insert a role in title field. thanks Leonardo

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  • Running tasks in the background with lower CPU priority

    - by Brendon Muir
    I have a feature in my CMS that allows a user to upload a zip file full of images and the server will extract them and insert each one into an image gallery. I've noticed that this grinds up the CPU quite severely and causes other requests to slow down. I'm thinking of using the delayed_job plugin to delegate each image addition into the background, but I also want to give that process a lower CPU priority so that it doesn't bog down the server. I'm pretty confident in the delaying part of the exercise, but the throttling part is where I'm stuck. Is there a ruby way of lowering the priority of a method call? It's the image resizing that causes the CPU chew. Any ideas welcome :)

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  • Code Golf: Banknote calculator

    - by paxdiablo
    This question was posted by a C beginner and it was an exercise to calculate, given a dollar value input by the user, the minimum number of bills (or banknotes, depending on your locale) needed to reach that dollar value. So, if the user entered 93, the output would be: $20 bills = 4 $10 bills = 1 $5 bills = 0 $1 bills = 3 Finally succumbing to the phenomenon (it's a slow day here), I thought this would be ripe for a game of Code Golf. For fairness, the input prompt needs to be (note the "_" at the end is a space): Enter a dollar amount:_ I think I've covered all the bases: no identical question, community wiki. I won't be offended if it gets shut down though - of course, I'll never be able to complain about these types of questions again, for fear of being labelled a hypocrite :-) Okay, let's see what you can come up with. Here's a sample run: Enter a dollar amount: 127 $20 bills = 6 $10 bills = 0 $5 bills = 1 $1 bills = 2

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  • Firefox add-on tab-specific buttons and scripts, similar to Page Actions in Google Chrome

    - by Chetan
    I want to write a Firefox extension that acts exactly like the built-in RSS feed scanner (as an exercise). It should do the following: On each new page / tab load, it should scan the content of the page for RSS feeds If there are RSS feeds in the page, it should put a button in the location bar that the user can click On clicking the button, a speech bubble should appear under the button (the way a speech bubble appears under the bookmarks star when you click on it), with information on the feeds and buttons to subscribe to them So my main questions are: What is the process to run specific content scripts for specific pages? What is the process to use the results of those scripts to update the speech bubble for each location bar button for each tab? Basically, I'm trying to figure out how to do in Firefox what Page Actions are in Google Chrome. Please help! :)

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  • Pythonic way of adding "ly" to end of string if it ends in "ing"?

    - by Sergio Tapia
    This is my first effort on solving the exercise. I gotta say, I'm kind of liking Python. :D # D. verbing # Given a string, if its length is at least 3, # add 'ing' to its end. # Unless it already ends in 'ing', in which case # add 'ly' instead. # If the string length is less than 3, leave it unchanged. # Return the resulting string. def verbing(s): if len(s) >= 3: if s[-3:] == "ing": s += "ly" else: s += "ing" return s else: return s # +++your code here+++ return What do you think I could improve on here?

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  • Is this the 'Pythonic' way of doing things?

    - by Sergio Tapia
    This is my first effort on solving the exercise. I gotta say, I'm kind of liking Python. :D # D. verbing # Given a string, if its length is at least 3, # add 'ing' to its end. # Unless it already ends in 'ing', in which case # add 'ly' instead. # If the string length is less than 3, leave it unchanged. # Return the resulting string. def verbing(s): if len(s) >= 3: if s[-3:] == "ing": s += "ly" else: s += "ing" return s else: return s # +++your code here+++ return What do you think I could improve on here?

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  • Python Bitstream implementations

    - by Danielb
    I am writing a huffman implementation in Python as a learning exercise. I have got to the point of writing out my variable length huffman codes to a buffer (or file). Only to find there does not seem to be a bitstream class implemented by Python! I have had a look at the array and struct modules but they do not seem to do what I need without extra work. A bit of goggling turned up this bitstream implementation, which is more like what I am wanting. Is there really no comparable bitstream class in the Python standard library?

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  • Restaurant review site in SharePoint

    - by Sisiutl
    I'm totally new to SharePoint but my company has adopted it for internal use. As a learning exercise I thought it would be fun to create a local restaurant review site. Can anyone point me to an example or tutorial to get me started? What I have in mind is a simple site where users can enter the restaurant name, cuisine style, address, a simple 5 point rating and price scale, and a short review. Other users could search for restaurants by cuisine and add their own reviews. We have SharePoint 2007 and MOSS. Thanks

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  • Explaining persistent data structures in simple terms

    - by Jason Baker
    I'm working on a library for Python that implements some persistent data structures (mainly as a learning exercise). However, I'm beginning to learn that explaining persistent data structures to people unfamiliar with them can be difficult. Can someone help me think of an easy (or at least the least complicated) way to describe persistent data structures to them? I've had a couple of people tell me that the documentation that I have is somewhat confusing. (And before anyone asks, no I don't mean persistent data structures as in persisted to the file system. Google persistent data structures if you're unclear on this.)

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  • Efficient heaps in purely functional languages

    - by Kim
    As an exercise in Haskell, I'm trying to implement heapsort. The heap is usually implemented as an array in imperative languages, but this would be hugely inefficient in purely functional languages. So I've looked at binary heaps, but everything I found so far describes them from an imperative viewpoint and the algorithms presented are hard to translate to a functional setting. How to efficiently implement a heap in a purely functional language such as Haskell? Edit: By efficient I mean it should still be in O(n*log n), but it doesn't have to beat a C program. Also, I'd like to use purely functional programming. What else would be the point of doing it in Haskell?

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  • Branchless memory manager?

    - by Richard Fabian
    Anyone thought about how to write a memory manager (in C++) that is completely branch free? I've written a pool, a stack, a queue, and a linked list (allocating from the pool), but I am wondering how plausible it is to write a branch free general memory manager. This is all to help make a really reusable framework for doing solid concurrent, in-order CPU, and cache friendly development. Edit: by branchless I mean without doing direct or indirect function calls, and without using ifs. I've been thinking that I can probably implement something that first changes the requested size to zero for false calls, but haven't really got much more than that. I feel that it's not impossible, but the other aspect of this exercise is then profiling it on said "unfriendly" processors to see if it's worth trying as hard as this to avoid branching.

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  • Idiomatic usage of filter, map, build-list and local functions in Racket/Scheme?

    - by Greenhorn
    I'm working through Exercise 21.2.3 of HtDP on my own and was wondering if this is idiomatic usage of the various functions. This is what I have so far: (define-struct ir (name price)) (define list-of-toys (list (make-ir 'doll 10) (make-ir 'robot 15) (make-ir 'ty 21) (make-ir 'cube 9))) ;; helper function (define (price< p toy) (cond [(< (ir-price toy) p) toy] [else empty])) (define (eliminate-exp ua lot) (cond [(empty? lot) empty] [else (filter ir? (map price< (build-list (length lot) (local ((define (f x) ua)) f)) lot))])) To my novice eyes, that seems pretty ugly because I have to define a local function to get build-list to work, since map requires two lists of equal length. Can this be improved for readability? Thank you.

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  • Parallelism in Python

    - by fmark
    What are the options for achieving parallelism in Python? I want to perform a bunch of CPU bound calculations over some very large rasters, and would like to parallelise them. Coming from a C background, I am familiar with three approaches to parallelism: Message passing processes, possibly distributed across a cluster, e.g. MPI. Explicit shared memory parallelism, either using pthreads or fork(), pipe(), et. al Implicit shared memory parallelism, using OpenMP. Deciding on an approach to use is an exercise in trade-offs. In Python, what approaches are available and what are their characteristics? Is there a clusterable MPI clone? What are the preferred ways of achieving shared memory parallelism? I have heard reference to problems with the GIL, as well as references to tasklets. In short, what do I need to know about the different parallelization strategies in Python before choosing between them?

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  • Why do I not get the correct answer for Euler 56 in J?

    - by Gregory Higley
    I've solved 84 of the Project Euler problems, mostly in Haskell. I am now going back and trying to solve in J some of those I already solved in Haskell, as an exercise in learning J. Currently, I am trying to solve Problem 56. Let me stress that I already know what the right answer is, since I've already solved it in Haskell. It's a very easy, trivial problem. I will not give the answer here. Here is my solution in J: digits =: ("."0)":"0 eachDigit =: adverb : 'u@:digits"0' NB. I use this so often I made it an adverb. cartesian =: adverb : '((#~ #) u ($~ ([:*~#)))' >./ +/ eachDigit x: ^ cartesian : i. 99 This produces a number less than the desired result. In other words, it's wrong somehow. Any J-ers out there know why? I'm baffled, since it's pretty straightforward and totally brute force.

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  • Implement a vpn

    - by jackson
    I want to build an application client(client.exe) - server to do the following: when the clients run it they are thrown in a VPN and they can communicate each other within 1 applicataion. For example : clients run client.exe and they can see each other in LAN ONLY in Starcraft. From what i have read the right type of vpn for this situation is Secured Socket Tunneling Protocol: "Secure socket tunneling protocol, also referred to as SSTP, is by definition an application-layer protocol. It is designed to employ a synchronous communication in a back and forth motion between two programs. It allows many application endpoints over one network connection, between peer nodes, thereby enabling efficient usage of the communication resources that are available to that network. " Question: I don't have experience with networking programming so my question for the ones who have, is this the right approach? PS1: i don't want something done like OpenVpn, i do this as learning exercise. PS2: the application is targeting Windows and i plan to use .NET Thanks for reading the whole story, i am waiting for your replies.

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