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  • Code golf: combining multiple sorted lists into a single sorted list

    - by Alabaster Codify
    Implement an algorithm to merge an arbitrary number of sorted lists into one sorted list. The aim is to create the smallest working programme, in whatever language you like. For example: input: ((1, 4, 7), (2, 5, 8), (3, 6, 9)) output: (1, 2, 3, 4, 5, 6, 7, 8, 9) input: ((1, 10), (), (2, 5, 6, 7)) output: (1, 2, 5, 6, 7, 10) Note: solutions which concatenate the input lists then use a language-provided sort function are not in-keeping with the spirit of golf, and will not be accepted: sorted(sum(lists,[])) # cheating: out of bounds! Apart from anything else, your algorithm should be (but doesn't have to be) a lot faster! Clearly state the language, any foibles and the character count. Only include meaningful characters in the count, but feel free to add whitespace to the code for artistic / readability purposes. To keep things tidy, suggest improvement in comments or by editing answers where appropriate, rather than creating a new answer for each "revision". EDIT: if I was submitting this question again, I would expand on the "no language provided sort" rule to be "don't concatenate all the lists then sort the result". Existing entries which do concatenate-then-sort are actually very interesting and compact, so I won't retro-actively introduce a rule they break, but feel free to work to the more restrictive spec in new submissions. Inspired by http://stackoverflow.com/questions/464342/combining-two-sorted-lists-in-python

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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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  • 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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  • Continue Considered Harmful?

    - by brian
    Should developers avoid using continue in C# or its equivalent in other languages to force the next iteration of a loop? Would arguments for or against overlap with arguments about Goto?

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  • Why is it useful to count the number of bits?

    - by Scorchin
    I've seen the numerous questions about counting the number of set bits in a insert type of input, but why is it useful? For those looking for algorithms about bit counting, look here: http://stackoverflow.com/questions/1517848/counting-common-bits-in-a-sequence-of-unsigned-longs http://stackoverflow.com/questions/472325/fastest-way-to-count-number-of-bit-transitions-in-an-unsigned-int http://stackoverflow.com/questions/109023/best-algorithm-to-count-the-number-of-set-bits-in-a-32-bit-integer

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  • Have you ever crashed the compiler?

    - by Motti
    Everyone (at least everyone who uses a compiled language) has faced compilation errors but how many times do you get to actually crash the compiler? I've had my fair share of "internal compiler errors" but most went away just by re-compiling. Do you have a (minimal) piece of code that crashes the compiler?

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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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  • Linear feedback shift register?

    - by Mattia Gobbi
    Lately I bumped repeatedly into the concept of LFSR, that I find quite interesting because of its links with different fields and also fascinating in itself. It took me some effort to understand, the final help was this really good page, much better than the (at first) cryptic wikipedia entry. So I wanted to write some small code for a program that worked like a LFSR. To be more precise, that somehow showed how a LFSR works. Here's the cleanest thing I could come up with after some lenghtier attempts (Python): def lfsr(seed, taps): sr, xor = seed, 0 while 1: for t in taps: xor += int(sr[t-1]) if xor%2 == 0.0: xor = 0 else: xor = 1 print xor sr, xor = str(xor) + sr[:-1], 0 print sr if sr == seed: break lfsr('11001001', (8,7,6,1)) #example I named "xor" the output of the XOR function, not very correct. However, this is just meant to show how it circles through its possible states, in fact you noticed the register is represented by a string. Not much logical coherence. This can be easily turned into a nice toy you can watch for hours (at least I could :-) def lfsr(seed, taps): import time sr, xor = seed, 0 while 1: for t in taps: xor += int(sr[t-1]) if xor%2 == 0.0: xor = 0 else: xor = 1 print xor print time.sleep(0.75) sr, xor = str(xor) + sr[:-1], 0 print sr print time.sleep(0.75) Then it struck me, what use is this in writing software? I heard it can generate random numbers; is it true? how? So, it would be nice if someone could: explain how to use such a device in software development come up with some code, to support the point above or just like mine to show different ways to do it, in any language Also, as theres not much didactic stuff around about this piece of logic and digital circuitry, it would be nice if this could be a place for noobies (like me) to get a better understanding of this thing, or better, to understand what it is and how it can be useful when writing software. Should have made it a community wiki? That said, if someone feels like golfing... you're welcome.

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  • Segmenting a double array of labels

    - by Ami
    The Problem: I have a large double array populated with various labels. Each element (cell) in the double array contains a set of labels and some elements in the double array may be empty. I need an algorithm to cluster elements in the double array into discrete segments. A segment is defined as a set of pixels that are adjacent within the double array and one label that all those pixels in the segment have in common. (Diagonal adjacency doesn't count and I'm not clustering empty cells). |-------|-------|------| | Jane | Joe | | | Jack | Jane | | |-------|-------|------| | Jane | Jane | | | | Joe | | |-------|-------|------| | | Jack | Jane | | | Joe | | |-------|-------|------| In the above arrangement of labels distributed over nine elements, the largest cluster is the “Jane” cluster occupying the four upper left cells. What I've Considered: I've considered iterating through every label of every cell in the double array and testing to see if the cell-label combination under inspection can be associated with a preexisting segment. If the element under inspection cannot be associated with a preexisting segment it becomes the first member of a new segment. If the label/cell combination can be associated with a preexisting segment it associates. Of course, to make this method reasonable I'd have to implement an elaborate hashing system. I'd have to keep track of all the cell-label combinations that stand adjacent to preexisting segments and are in the path of the incrementing indices that are iterating through the double array. This hash method would avoid having to iterate through every pixel in every preexisting segment to find an adjacency. Why I Don't Like it: As is, the above algorithm doesn't take into consideration the case where an element in the double array can be associated with two unique segments, one in the horizontal direction and one in the vertical direction. To handle these cases properly, I would need to implement a test for this specific case and then implement a method that will both associate the element under inspection with a segment and then concatenate the two adjacent identical segments. On the whole, this method and the intricate hashing system that it would require feels very inelegant. Additionally, I really only care about finding the large segments in the double array and I'm much more concerned with the speed of this algorithm than with the accuracy of the segmentation, so I'm looking for a better way. I assume there is some stochastic method for doing this that I haven't thought of. Any suggestions?

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  • How to use a DHT for a social trading environment

    - by Lirik
    I'm trying to understand if a DHT can be used to solve a problem I'm working on: I have a trading environment where professional option traders can get an increase in their risk limit by requesting that fellow traders lend them some of their risk limit. The lending trader will can either search for traders with certain risk parameters which are part of every trader's profile, i.e. Greeks, or the lending trader can subscribe to requests from certain traders. I want this environment to be scalable and decentralized, but I don't know how traders can search for specific profile parameters when the data is contained in a DHT. Could anybody explain how this can be done?

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  • Based on your development stack, which is easier for you and why? Debugging or logging?

    - by leeand00
    Please state if you are developing on the front end, back end, or if you are developing a mobile/desktop application. List your development stack Language, IDE, etc.. Unit Testing or no Unit Testing Be sure to include any AOP frameworks if used. Tell me if it is easier for you to use debugging or to using logging during development, and why you feel it is easier. I'm just trying to get a feel for why people choose debugging or logging based on their development stack.

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  • Why do static Create methods exist?

    - by GeReV
    I was wondering, why do static Create methods exist? For instance, why use this code: System.Xml.XmlReader reader = System.Xml.XmlReader.Create(inputUri); over this code: System.Xml.XmlReader reader = new System.Xml.XmlReader(inputUri); I cannot find the rationale for using one over the other, and can't find any relation between classes who use this construct over the other. Can anyone shed some light on this?

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  • How do you get your self focused with so many distractions around? (which you can't or don't want to

    - by Teja Kantamneni
    This question is definitely for a programmer and is centric towards a programmer. But if somebody feels it should not belong here I would not mind deleting it. I don't think this need to go as a WIKI, but if feel like it is a WIKI, I can do that too. The Question is: As a programmer you have to keep yourself up to date with the latest technologies and for that every programmer will generally follow some technology blogs and some social networking sites like (twitter, FB, SO, DZONE etc), how to keep your self focused on the things and still want to follow the technology trends? No Subjective or argumentative answers, Just want to know what practices other fellow programmers do for this...

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  • What's your most controversial programming opinion?

    - by Jon Skeet
    This is definitely subjective, but I'd like to try to avoid it becoming argumentative. I think it could be an interesting question if people treat it appropriately. The idea for this question came from the comment thread from my answer to the "What are five things you hate about your favorite language?" question. I contended that classes in C# should be sealed by default - I won't put my reasoning in the question, but I might write a fuller explanation as an answer to this question. I was surprised at the heat of the discussion in the comments (25 comments currently). So, what contentious opinions do you hold? I'd rather avoid the kind of thing which ends up being pretty religious with relatively little basis (e.g. brace placing) but examples might include things like "unit testing isn't actually terribly helpful" or "public fields are okay really". The important thing (to me, anyway) is that you've got reasons behind your opinions. Please present your opinion and reasoning - I would encourage people to vote for opinions which are well-argued and interesting, whether or not you happen to agree with them.

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  • Code golf: Word frequency chart

    - by ChristopheD
    The challenge: Build an ASCII chart of the most commonly used words in a given text. The rules: Only accept a-z and A-Z (alphabetic characters) as part of a word. Ignore casing (She == she for our purpose). Ignore the following words (quite arbitary, I know): the, and, of, to, a, i, it, in, or, is Clarification: considering don't: this would be taken as 2 different 'words' in the ranges a-z and A-Z: (don and t). Optionally (it's too late to be formally changing the specifications now) you may choose to drop all single-letter 'words' (this could potentially make for a shortening of the ignore list too). Parse a given text (read a file specified via command line arguments or piped in; presume us-ascii) and build us a word frequency chart with the following characteristics: Display the chart (also see the example below) for the 22 most common words (ordered by descending frequency). The bar width represents the number of occurences (frequency) of the word (proportionally). Append one space and print the word. Make sure these bars (plus space-word-space) always fit: bar + [space] + word + [space] should be always <= 80 characters (make sure you account for possible differing bar and word lenghts: e.g.: the second most common word could be a lot longer then the first while not differing so much in frequency). Maximize bar width within these constraints and scale the bars appropriately (according to the frequencies they represent). An example: The text for the example can be found here (Alice's Adventures in Wonderland, by Lewis Carroll). This specific text would yield the following chart: _________________________________________________________________________ |_________________________________________________________________________| she |_______________________________________________________________| you |____________________________________________________________| said |____________________________________________________| alice |______________________________________________| was |__________________________________________| that |___________________________________| as |_______________________________| her |____________________________| with |____________________________| at |___________________________| s |___________________________| t |_________________________| on |_________________________| all |______________________| this |______________________| for |______________________| had |_____________________| but |____________________| be |____________________| not |___________________| they |__________________| so For your information: these are the frequencies the above chart is built upon: [('she', 553), ('you', 481), ('said', 462), ('alice', 403), ('was', 358), ('that ', 330), ('as', 274), ('her', 248), ('with', 227), ('at', 227), ('s', 219), ('t' , 218), ('on', 204), ('all', 200), ('this', 181), ('for', 179), ('had', 178), (' but', 175), ('be', 167), ('not', 166), ('they', 155), ('so', 152)] A second example (to check if you implemented the complete spec): Replace every occurence of you in the linked Alice in Wonderland file with superlongstringstring: ________________________________________________________________ |________________________________________________________________| she |_______________________________________________________| superlongstringstring |_____________________________________________________| said |______________________________________________| alice |________________________________________| was |_____________________________________| that |______________________________| as |___________________________| her |_________________________| with |_________________________| at |________________________| s |________________________| t |______________________| on |_____________________| all |___________________| this |___________________| for |___________________| had |__________________| but |_________________| be |_________________| not |________________| they |________________| so The winner: Shortest solution (by character count, per language). Have fun! Edit: Table summarizing the results so far (2012-02-15) (originally added by user Nas Banov): Language Relaxed Strict ========= ======= ====== GolfScript 130 143 Perl 185 Windows PowerShell 148 199 Mathematica 199 Ruby 185 205 Unix Toolchain 194 228 Python 183 243 Clojure 282 Scala 311 Haskell 333 Awk 336 R 298 Javascript 304 354 Groovy 321 Matlab 404 C# 422 Smalltalk 386 PHP 450 F# 452 TSQL 483 507 The numbers represent the length of the shortest solution in a specific language. "Strict" refers to a solution that implements the spec completely (draws |____| bars, closes the first bar on top with a ____ line, accounts for the possibility of long words with high frequency etc). "Relaxed" means some liberties were taken to shorten to solution. Only solutions shorter then 500 characters are included. The list of languages is sorted by the length of the 'strict' solution. 'Unix Toolchain' is used to signify various solutions that use traditional *nix shell plus a mix of tools (like grep, tr, sort, uniq, head, perl, awk).

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  • What should every programmer know?

    - by Matt Lacey
    Regardless of programming language(s) or operating system(s) used or the environment they develop for, what should every programmer know? Some background: I'm interested in becoming the best programmer I can. As part of this process I'm trying to understand what I don't know and would benefit me a lot if I did. While there are loads of lists around along the lines of "n things every [insert programming language] developer should know", I have yet to find anything similar which isn't limited to a specific language. I also expect this information to be of interest and benefit to others.

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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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  • 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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  • Have you been in cases where TDD increased development time?

    - by BillyONeal
    Hello everyone :) I was reading http://stackoverflow.com/questions/2512504/tdd-how-to-start-really-thinking-tdd and I noticed many of the answers indicate that tests + application should take less time than just writing the application. In my experience, this is not true. My problem though is that some 90% of the code I write has a TON of operating system calls. The time spent to actually mock these up takes much longer than just writing the code in the first place. Sometimes 4 or 5 times as long to write the test as to write the actual code. I'm curious if there are other developers in this kind of a scenario.

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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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  • What is a Windows scripting language that: does not rely on .NET and offers the most OOP support and

    - by jJack
    What is a Windows scripting language that: does not rely on .NET and offers the most OOP support and has simplest deployment? It doesn't necessarily need to be a scripting language; It can be in the form of a compiled executable, however it needs to be self contained--only ONE file, no DLL's and it cannot be declared to "include" other files. I cannot rely on the user having any .NET installed and it needs to be able to run on Windows 7 64 bit. By "most OOP support", I basically mean anything that has better OOP support than VBScript. A little context: Everything I have done thus far is in VBScript and writes a bunch of data into an .html file, which in the end is to be viewed by Internet Explorer. It also zips up a bunch of directories and files. It heavily relies on accessing the registry, file-system, and WMI (I can probably do without accessing WMI though, as long as I have good registry access). I can bring myself to code in any language so long as it meets me ridonkulous requirements stated above. I look forward to some good answers from those more experienced than I.

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