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  • Is a red-black tree my ideal data structure?

    - by Hugo van der Sanden
    I have a collection of items (big rationals) that I'll be processing. In each case, processing will consist of removing the smallest item in the collection, doing some work, and then adding 0-2 new items (which will always be larger than the removed item). The collection will be initialised with one item, and work will continue until it is empty. I'm not sure what size the collection is likely to reach, but I'd expect in the range 1M-100M items. I will not need to locate any item other than the smallest. I'm currently planning to use a red-black tree, possibly tweaked to keep a pointer to the smallest item. However I've never used one before, and I'm unsure whether my pattern of use fits its characteristics well. 1) Is there a danger the pattern of deletion from the left + random insertion will affect performance, eg by requiring a significantly higher number of rotations than random deletion would? Or will delete and insert operations still be O(log n) with this pattern of use? 2) Would some other data structure give me better performance, either because of the deletion pattern or taking advantage of the fact I only ever need to find the smallest item? Update: glad I asked, the binary heap is clearly a better solution for this case, and as promised turned out to be very easy to implement. Hugo

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  • When is performance gain significant enough to implement that optimization?

    - by Zwei steinen
    Hi, following the text book, I do measure performance whenever I try optimizing my code. Sometimes, however, the performance gain is rather small and I can't decisively decide whether I should implement that optimization. For example, when a fix shortens an average response time of 100ms to 90ms under some conditions, should I implement that fix? What if it shortens 200ms to 190ms? How many condition should I try before I can conclude that it will be beneficial overall? I guess it's not possible to give a straight forward answer to this, as it depends on too many things, but is there a good rule of thumb that I should follow? Are there any guideline/best-practices?

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  • Theory of formal languages - Automaton

    - by dader51
    Hi everybody ! I'm wondering about formal languages. I have a kind of parser : It reads à xml-like serialized tree structure and turn it into a multidimmensionnal array. I figured out that i need at least three variables to achieve the job : $tree = array(); // a new array $pTree = array(&$tree); // a new array which the first element points to $tree; $deep = 0; plus the one containing the sentence splitted into words. My point is on the similarities between the algorithm deing used and the differents kinds of automatons ( state machines turing machines stack ... ). The $words variable is the "tape" of the automaton, the test/conditions of the algorithm are transitions, $deep is the state and $tree is the output. I cannont figure what is $pTree. So the question is : which is the automaton I implictly use here, and to which formal languages family does it fit ? And what's about recursion ?

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  • Is OO design's strength in semantics or encapsulation?

    - by Phil H
    Object-oriented design (OOD) combines data and its methods. This, as far as I can see, achieves two great things: it provides encapsulation (so I don't care what data there is, only how I get values I want) and semantics (it relates the data together with names, and its methods consistently use the data as originally intended). So where does OOD's strength lie? In constrast, functional programming attributes the richness to the verbs rather than the nouns, and so both encapsulation and semantics are provided by the methods rather than the data structures. I work with a system that is on the functional end of the spectrum, and continually long for the semantics and encapsulation of OO. But I can see that OO's encapsulation can be a barrier to flexible extension of an object. So at the moment, I can see the semantics as a greater strength. Or is encapsulation the key to all worthwhile code?

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  • Where does "foo" come from in coding examples? [closed]

    - by ThePower
    Possible Duplicates: Using “Foo” and “Bar” in examples To foo bar, or not to foo bar: that is the question. Possible Duplicates: Using "Foo" and "Bar" in examples To foo bar, or not to foo bar: that is the question. Bit of a general question here, but it's something I would like to know! Whenever I am looking for resolutions to my C# problems online, I always come across "foo" being used as an example. Does this represent anything or is it just one of those unexplained catchy object names, used by many people in examples?

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  • Find location using only distance and range?

    - by pinnacler
    Triangulation works by checking your angle to three KNOWN targets. "I know the that's the Lighthouse of Alexandria, it's located here (X,Y) on a map, and it's to my right at 90 degrees." Repeat 2 more times for different targets and angles. Trilateration works by checking your distance from three KNOWN targets. "I know the that's the Lighthouse of Alexandria, it's located here (X,Y) on a map, and I'm 100 meters away from that." Repeat 2 more times for different targets and ranges. But both of those methods rely on knowing WHAT you're looking at. Say you're in a forest and you can't differentiate between trees, but you know where key trees are. These trees have been hand picked as "landmarks." You have a robot moving through that forest slowly. Do you know of any ways to determine location based solely off of angle and range, exploiting geometry between landmarks? Note, you will see other trees as well, so you won't know which trees are key trees. Ignore the fact that a target may be occluded. Our pre-algorithm takes care of that. 1) If this exists, what's it called? I can't find anything. 2) What do you think the odds are of having two identical location 'hits?' I imagine it's fairly rare. 3) If there are two identical location 'hits,' how can I determine my exact location after I move the robot next. (I assume the chances of having 2 occurrences of EXACT angles in a row, after I reposition the robot, would be statistically impossible, barring a forest growing in rows like corn). Would I just calculate the position again and hope for the best? Or would I somehow incorporate my previous position estimate into my next guess? If this exists, I'd like to read about it, and if not, develop it as a side project. I just don't have time to reinvent the wheel right now, nor have the time to implement this from scratch. So if it doesn't exist, I'll have to figure out another way to localize the robot since that's not the aim of this research, if it does, lets hope it's semi-easy.

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  • As our favorite imperative languages gain functional constructs, should loops be considered a code s

    - by Michael Buen
    In allusion to Dare Obasanjo's impressions on Map, Reduce, Filter (Functional Programming in C# 3.0: How Map/Reduce/Filter can Rock your World) "With these three building blocks, you could replace the majority of the procedural for loops in your application with a single line of code. C# 3.0 doesn't just stop there." Should we increasingly use them instead of loops? And should be having loops(instead of those three building blocks of data manipulation) be one of the metrics for coding horrors on code reviews? And why? [NOTE] I'm not advocating fully functional programming on those codes that could be simply translated to loops(e.g. tail recursions) Asking for politer term. Considering that the phrase "code smell" is not so diplomatic, I posted another question http://stackoverflow.com/questions/432492/whats-the-politer-word-for-code-smell about the right word for "code smell", er.. utterly bad code. Should that phrase have a place in our programming parlance?

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  • Are there any well known algorithms to detect the presence of names?

    - by Rhubarb
    For example, given a string: "Bob went fishing with his friend Jim Smith." Bob and Jim Smith are both names, but bob and smith are both words. Weren't for them being uppercase, there would be less indication of this outside of our knowledge of the sentence. Without doing grammar analysis, are there any well known algorithms for detecting the presence of names, at least Western names?

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  • Find all complete sub-graphs within a graph

    - by mvid
    Is there a known algorithm or method to find all complete sub-graphs within a graph? I have an undirected, unweighted graph and I need to find all subgraphs within it where each node in the subgraph is connected to each other node in the subgraph. Is there an existing algorithm for this?

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  • Function overloading by return type?

    - by dsimcha
    Why don't more mainstream statically typed languages support function/method overloading by return type? I can't think of any that do. It seems no less useful or reasonable than supporting overload by parameter type. How come it's so much less popular?

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  • Encode complex number as RGB pixel and back

    - by Vi
    How is it better to encode a complex number into RGB pixel and vice versa? Probably (logarithm of) an absolute value goes to brightness and an argument goes to hue. Desaturated pixes should receive randomized argument in reverse transformation. Something like: 0 - (0,0,0) 1 - (255,0,0) -1 - (0,255,255) 0.5 - (128,0,0) i - (255,255,0) -i - (255,0,255) (0,0,0) - 0 (255,255,255) - e^(i * random) (128,128,128) - 0.5 * e^(i *random) (0,128,128) - -0.5 Are there ready-made formulas for that? Edit: Looks like I just need to convert RGB to HSB and back. Edit 2: Existing RGB - HSV converter fragment: if (hsv.sat == 0) { hsv.hue = 0; // ! return hsv; } I don't want 0. I want random. And not just if hsv.sat==0, but if it is lower that it should be ("should be" means maximum saturation, saturation that is after transformation from complex number).

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  • Autotesting a network interface

    - by Machado
    Hi All, I'm developing a software component responsible for testing if a network interface has conectivity with the internet. Think of it as the same test the XBOX360 does to inform the user if it's connected with the Live network (just as an example). So far I figured the autotest would run as this: 1) Test the physical network interface (if the cable is conected, has up/downlink, etc...) 2) Test the logical network (has IP address, has DNS, etc...) 3) Connects to the internet (can access google, for example) 4) ??? 5) Profit! (just kidding...) My question relates to step 3: How can I detect, correctly, if my software has connection with the internet ? Is there any fixed IP address to ping ? The problem is that I don't want to rely solely on google.com (or any other well-known address), as those can change in time, and my component will be embbeded on a mobile device, not easy to update. Any suggestions ?

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  • Are licenses relevant for small code snippets?

    - by Martin
    When I'm about to write a short algorithm, I first check in the base class library I'm using whether the algorithm is implemented in it. If not, I often do a quick google search to see if someone has done it before (which is the case, 19 times out of 20). Most of the time, I find the exact code I need. Sometimes it's clear what license applies to the source code, sometimes not. It may be GPL, LGPL, BSD or whatever. Sometimes people have posted a code snippet on some random forum which solves my problem. It's clear to me that I can't reuse the code (copy/paste it into my code) without caring about the license if the code is in some way substantial. What is not clear to me is whether I can copy a code snippet containing 5 lines or so without doing a license violation. Can I copy/paste a 5-line code snippet without caring about the license? What about one-liner? What about 10 lines? Where do I draw the line (no pun intended)? My second problem is that if I have found a 10-line code snippet which does exactly what I need, but feel that I cannot copy it because it's GPL-licensed and my software isn't, I have already memorized how to implement it so when I go around implementing the same functionality, my code is almost identical to the GPL licensed code I saw a few minutes ago. (In other words, the code was copied to my brain and my brain after that copied it into my source code).

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  • Examples of monoids/semigroups in programming

    - by jkff
    It is well-known that monoids are stunningly ubiquitous in programing. They are so ubiquitous and so useful that I, as a 'hobby project', am working on a system that is completely based on their properties (distributed data aggregation). To make the system useful I need useful monoids :) I already know of these: Numeric or matrix sum Numeric or matrix product Minimum or maximum under a total order with a top or bottom element (more generally, join or meet in a bounded lattice, or even more generally, product or coproduct in a category) Set union Map union where conflicting values are joined using a monoid Intersection of subsets of a finite set (or just set intersection if we speak about semigroups) Intersection of maps with a bounded key domain (same here) Merge of sorted sequences, perhaps with joining key-equal values in a different monoid/semigroup Bounded merge of sorted lists (same as above, but we take the top N of the result) Cartesian product of two monoids or semigroups List concatenation Endomorphism composition. Now, let us define a quasi-property of an operation as a property that holds up to an equivalence relation. For example, list concatenation is quasi-commutative if we consider lists of equal length or with identical contents up to permutation to be equivalent. Here are some quasi-monoids and quasi-commutative monoids and semigroups: Any (a+b = a or b, if we consider all elements of the carrier set to be equivalent) Any satisfying predicate (a+b = the one of a and b that is non-null and satisfies some predicate P, if none does then null; if we consider all elements satisfying P equivalent) Bounded mixture of random samples (xs+ys = a random sample of size N from the concatenation of xs and ys; if we consider any two samples with the same distribution as the whole dataset to be equivalent) Bounded mixture of weighted random samples Which others do exist?

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  • Finding what makes strings unique in a list, can you improve on brute force?

    - by Ed Guiness
    Suppose I have a list of strings where each string is exactly 4 characters long and unique within the list. For each of these strings I want to identify the position of the characters within the string that make the string unique. So for a list of three strings abcd abcc bbcb For the first string I want to identify the character in 4th position d since d does not appear in the 4th position in any other string. For the second string I want to identify the character in 4th position c. For the third string it I want to identify the character in 1st position b AND the character in 4th position, also b. This could be concisely represented as abcd -> ...d abcc -> ...c bbcb -> b..b If you consider the same problem but with a list of binary numbers 0101 0011 1111 Then the result I want would be 0101 -> ..0. 0011 -> .0.. 1111 -> 1... Staying with the binary theme I can use XOR to identify which bits are unique within two binary numbers since 0101 ^ 0011 = 0110 which I can interpret as meaning that in this case the 2nd and 3rd bits (reading left to right) are unique between these two binary numbers. This technique might be a red herring unless somehow it can be extended to the larger list. A brute-force approach would be to look at each string in turn, and for each string to iterate through vertical slices of the remainder of the strings in the list. So for the list abcd abcc bbcb I would start with abcd and iterate through vertical slices of abcc bbcb where these vertical slices would be a | b | c | c b | b | c | b or in list form, "ab", "bb", "cc", "cb". This would result in four comparisons a : ab -> . (a is not unique) b : bb -> . (b is not unique) c : cc -> . (c is not unique) d : cb -> d (d is unique) or concisely abcd -> ...d Maybe it's wishful thinking, but I have a feeling that there should be an elegant and general solution that would apply to an arbitrarily large list of strings (or binary numbers). But if there is I haven't yet been able to see it. I hope to use this algorithm to to derive minimal signatures from a collection of unique images (bitmaps) in order to efficiently identify those images at a future time. If future efficiency wasn't a concern I would use a simple hash of each image. Can you improve on brute force?

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  • Interface for classes that have nothing in common

    - by Tomek Tarczynski
    Lets say I want to make few classes to determine behaviour of agents. The good practice would be to make some common interface for them, such interface (simplified) could look like this: interface IModel { void UpdateBehaviour(); } All , or at least most, of such model would have some parameters, but parameters from one model might have nothing in common with parameters of other model. I would like to have some common way of loading parameters. Question What is the best way to do that? Is it maybe just adding method void LoadParameters(object parameters) to the IModel? Or creating empty interface IParameters and add method void LoadParameters(IParameters parameters)? That are two ideas I came up with, but I don't like either of them.

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  • Using different languages in one project

    - by Tarbal
    I recently heard about the use of several different languages in a (big) project, I also read about famous services such as Twitter using Rails as frontend, mixed with some other languages, and Scala I think it was as backend. Is this common practice? Who does that? I'm sure there are disadvantages to this. I think that you will have problems with the different interpreters/compilers and seamlessly connecting the different languages. Is this true? Why is this actually done? For performance?

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  • Is there any way to set or code breakpoints conditionally?

    - by froadie
    I've been wondering this for a while - is there a way to code/program breakpoints...? Conditionally? For example, can I specify something like - "when this variable becomes this value, break and open the debugger"? (Would be quite useful, especially in long loops when you want to debug loop execution of a late loop value.) I suppose this may be IDE-specific since debugging is implemented differently in different IDEs... I'd be interested to know how to do this in any IDE, but specifically in Eclipse and Visual Studio.

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