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• Travelling Salesman Problem Constraint Representation

  - by alex25

  Hey! I read a couple of articles and sample code about how to solve TSP with Genetic Algorithms and Ant Colony Optimization etc. But everything I found didn't include time (window) constraints, eg. "I have to be at customer x before 12am)" and assumed symmetry. Can somebody point me into the direction of some sample code or articles that explain how I can add constraints to TSP and how I can represent those in code. Thanks!

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• What is it about Fibonacci numbers?

  - by Ian Bishop

  Fibonacci numbers have become a popular introduction to recursion for Computer Science students and there's a strong argument that they persist within nature. For these reasons, many of us are familiar with them. They also exist within Computer Science elsewhere too; in surprisingly efficient data structures and algorithms based upon the sequence. There are two main examples that come to mind: Fibonacci heaps which have better amortized running time than binomial heaps. Fibonacci search which shares O(log N) running time with binary search on an ordered array. Is there some special property of these numbers that gives them an advantage over other numerical sequences? Is it a density quality? What other possible applications could they have? It seems strange to me as there are many natural number sequences that occur in other recursive problems, but I've never seen a Catalan heap.

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• How to generate a number in arbitrary range using random()={0..1} preserving uniformness and density?

  - by psihodelia

  Generate a random number in range [x..y] where x and y are any arbitrary floating point numbers. Use function random(), which returns a random floating point number in range [0..1] from P uniformly distributed numbers (call it "density"). Uniform distribution must be preserved and P must be scaled as well. I think, there is no easy solution for such problem. To simplify it a bit, I ask you how to generate a number in interval [-0.5 .. 0.5], then in [0 .. 2], then in [-2 .. 0], preserving uniformness and density? Thus, for [0 .. 2] it must generate a random number from P*2 uniformly distributed numbers. The obvious simple solution random() * (x - y) + y will generate not all possible numbers because of the lower density for all abs(x-y)>1.0 cases. Many possible values will be missed. Remember, that random() returns only a number from P possible numbers. Then, if you multiply such number by Q, it will give you only one of P possible values, scaled by Q, but you have to scale density P by Q as well.

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• Is there a name for the technique of using base-2 numbers to encode a list of unique options?

  - by Lunatik

  Apologies for the rather vague nature of this question, I've never been taught programming and Google is rather useless to a self-help guy like me in this case as the key words are pretty ambiguous. I am writing a couple of functions that encode and decode a list of options into a Long so they can easily be passed around the application, you know this kind of thing: 1 - Apple 2 - Orange 4 - Banana 8 - Plum etc. In this case the number 11 would represent Apple, Orange & Plum. I've got it working but I see this used all the time so assume there is a common name for the technique, and no doubt all sorts of best practice and clever algorithms that are at the moment just out of my reach.

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• Compact data structure for storing a large set of integral values

  - by Odrade

  I'm working on an application that needs to pass around large sets of Int32 values. The sets are expected to contain ~1,000,000-50,000,000 items, where each item is a database key in the range 0-50,000,000. I expect distribution of ids in any given set to be effectively random over this range. The operations I need on the set are dirt simple: Add a new value Iterate over all of the values. There is a serious concern about the memory usage of these sets, so I'm looking for a data structure that can store the ids more efficiently than a simple List<int>or HashSet<int>. I've looked at BitArray, but that can be wasteful depending on how sparse the ids are. I've also considered a bitwise trie, but I'm unsure how to calculate the space efficiency of that solution for the expected data. A Bloom Filter would be great, if only I could tolerate the false negatives. I would appreciate any suggestions of data structures suitable for this purpose. I'm interested in both out-of-the-box and custom solutions. EDIT: To answer your questions: No, the items don't need to be sorted By "pass around" I mean both pass between methods and serialize and send over the wire. I clearly should have mentioned this. There could be a decent number of these sets in memory at once (~100).

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• Shortcut key for moving between source and design view in ASP.net Pages

  - by Wael Dalloul

  I know that F7/Shift F7 will switch between Code behind and ASPX pages, but what's the shortcut to switch between source and design view in Visual studio for asp.net Pages?

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• Merge Sort a Linked List

  - by Andrew Peters

  I was recently brushing up on some fundamentals and found merge sorting a linked list to be a pretty good challenge. If you have a good implementation then show it off here.

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• Find the element with the most "neighbors" in a sequence

  - by Bao An

  Assume that we have a sequence S with n elements <x1,x2,...,xn>. A pair of elements xi,xj are considered neighbors if |xi-xj|<d, with d a given distance between two neighbors. So how can find out the element that has most neighbors in the sequence? (A simply way is sorting the sequence and then calculating number of each element but it's time complexity is quite large): O(nlogn) May you please help me find a better way to reduce time complexity?

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• Suggestions: Anti-Pattern counter-examples

  - by Tom W

  It doesn't seem that this exact question has been asked before, so I'll fire away: Most of us are familiar with the concept of an anti-pattern. However, avoiding implementation of anti-patterns can in principle swing too far the other way and cause problems itself. As an example, "Design by Committee" has a counter-example that I'd call "Design by Maverick" - wherein the design of an important feature is handed off to an individual to do what they think best, with the intention of reviewing their work later and deciding whether it should be finalised or go through another iteration. This takes much longer in practice as the rest of the team are occupied by other things, and can end up with a feature that's useful to nobody, particularly if the Maverick is not themselves an experienced end-user. Does anyone have any more examples of anti-pattern counter-examples?

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• C: Why some string.h algorithms work slower than simple hand-made ones?

  - by MInner

  For example, strlen() takes about 3*O(n). Why 3? I've wrote a really simple strlen-like function - it works much faster. int string_len(char s[],int &l) { for(l=0;s[l];l++); return l; } Well, some of my friends says, nearly all of string.h algorithms are slower than they should be.

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• How does Amazon's Statistically Improbable Phrases work?

  - by ??iu

  How does something like Statistically Improbable Phrases work? According to amazon: Amazon.com's Statistically Improbable Phrases, or "SIPs", are the most distinctive phrases in the text of books in the Search Inside!™ program. To identify SIPs, our computers scan the text of all books in the Search Inside! program. If they find a phrase that occurs a large number of times in a particular book relative to all Search Inside! books, that phrase is a SIP in that book. SIPs are not necessarily improbable within a particular book, but they are improbable relative to all books in Search Inside!. For example, most SIPs for a book on taxes are tax related. But because we display SIPs in order of their improbability score, the first SIPs will be on tax topics that this book mentions more often than other tax books. For works of fiction, SIPs tend to be distinctive word combinations that often hint at important plot elements. For instance, for Joel's first book, the SIPs are: leaky abstractions, antialiased text, own dog food, bug count, daily builds, bug database, software schedules One interesting complication is that these are phrases of either 2 or 3 words. This makes things a little more interesting because these phrases can overlap with or contain each other.

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• Typecasting a floating value or using the math.h floor* functions?

  - by nobody

  Hi, I am coding up an implementation of Interpolation Search in C. The question is actually rather simple, I need to use the floating operations to do linear interpolation to find the correct index which will eventually be an integer result. In particular my probe index is: t = i + floor((((k-low)/(high-low)) * (j-i))); where, i,j,k,t are unsigned ints, and high,low are doubles. Would this be equivalent to: t = i + (unsigned int)(((k-low)/(high-low)) * (j-i)); Is there any reason I would actually want to use math.h floor* functions over just a simple (int) typecast?

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• Aligning music notes using String matching algorithms or Dynamic Programming

  - by Dolphin

  Hi I need to compare 2 sets of musical pieces (i.e. a playing-taken in MIDI format-note details extracted and saved in a database table, against sheet music-taken into XML format). When evaluating playing against sheet music (i.e.note details-pitch, duration, rhythm), note alignment needs to be done - to identify missed/extra/incorrect/swapped notes that from the reference (sheet music) notes. I have like 1800-2500 notes in one piece approx (can even be more-with polyphonic, right now I'm doing for monophonic). So will I have to have all these into an array? Will it be memory overloading or stack overflow? There are string matching algorithms like KMP, Boyce-Moore. But note alignment can also be done through Dynamic Programming. How can I use Dynamic Programming to approach this? What are the available algorithms? Is it about approximate string matching? Which approach is much productive? String matching algos like Boyce-Moore, or dynamic programming? How can I assess which is more effective? Greatly appreciate any insight or suggestions Thanks in advance

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• How can I group an array of rectangles into "Islands" of connected regions?

  - by Eric

  The problem I have an array of java.awt.Rectangles. For those who are not familiar with this class, the important piece of information is that they provide an .intersects(Rectangle b) function. I would like to write a function that takes this array of Rectangles, and breaks it up into groups of connected rectangles. Lets say for example, that these are my rectangles (constructor takes the arguments x, y, width,height): Rectangle[] rects = new Rectangle[] { new Rectangle(0, 0, 4, 2), //A new Rectangle(1, 1, 2, 4), //B new Rectangle(0, 4, 8, 2), //C new Rectangle(6, 0, 2, 2) //D } A quick drawing shows that A intersects B and B intersects C. D intersects nothing. A tediously drawn piece of ascii art does the job too: +-------+ +---+ ¦A+---+ ¦ ¦ D ¦ +-+---+-+ +---+ ¦ B ¦ +-+---+---------+ ¦ +---+ C ¦ +---------------+ Therefore, the output of my function should be: new Rectangle[][]{ new Rectangle[] {A,B,C}, new Rectangle[] {D} } The failed code This was my attempt at solving the problem: public List<Rectangle> getIntersections(ArrayList<Rectangle> list, Rectangle r) { List<Rectangle> intersections = new ArrayList<Rectangle>(); for(Rectangle rect : list) { if(r.intersects(rect)) { list.remove(rect); intersections.add(rect); intersections.addAll(getIntersections(list, rect)); } } return intersections; } public List<List<Rectangle>> mergeIntersectingRects(Rectangle... rectArray) { List<Rectangle> allRects = new ArrayList<Rectangle>(rectArray); List<List<Rectangle>> groups = new ArrayList<ArrayList<Rectangle>>(); for(Rectangle rect : allRects) { allRects.remove(rect); ArrayList<Rectangle> group = getIntersections(allRects, rect); group.add(rect); groups.add(group); } return groups; } Unfortunately, there seems to be an infinite recursion loop going on here. My uneducated guess would be that java does not like me doing this: for(Rectangle rect : allRects) { allRects.remove(rect); //... } Can anyone shed some light on the issue?

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• Single dimension peak fitting

  - by bufferz

  I have a single dimensional array of floating point values (c# doubles FYI) and I need to find the "peak" of the values ... as if graphed. I can't just take the highest value, as the peak is actually a plateau that has small fluctuations. This plateau is in the middle of a bunch of noise. I'm looking find a solution that would give me the center of this plateau. An example array might look like this: 1,2,1,1,2,1,3,2,4,4,4,5,6,8,8,8,8,7,8,7,9,7,5,4,4,3,3,2,2,1,1,1,1,1,2,1,1,1,1 where the peak is somewhere in the bolded section. Any ideas?

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• How can I test if a point lies within a 3d shape with its surface defined by a point cloud?

  - by Ben

  Hi I have a collection of points which describe the surface of a shape that should be roughly spherical, and I need a method with which to determine if any other given point lies within this shape. I've previously been approximating the shape as an exact sphere, but this has proven too inaccurate and I need a more accurate method. Simplicity and speed is favourable over complete accuracy, a good approximation will suffice. I've come across techniques for converting a point cloud to a 3d mesh, but most things I have found have been very complicated, and I am looking for something as simple as possible. Any ideas? Many thanks, Ben.

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• How to scale JPEG image down so that text is clear as possible?

  - by Juha Syrjälä

  I have some JPEG images that I need scale down to about 80% of original size. Original image dimension are about 700px × 1000px. Images contain some computer generated text and possibly some graphics (similar to what you would find in corporate word documents). How to scale image so that the text is as legible as possible? Currently we are scaling the imaeg down using bicubic interpolation, but that makes the text blurry and foggy.

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• Efficiently solving sparse matrices

  - by anon

  For solving spare matrices, in general, how big does the matrix have to be (as a rule of thumb) for methods like congraduate descent to be faster than brute force solvers (that do not take advantage o sparsity)?

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• Explanation needed for sum of prime below n numbers

  - by Bala Krishnan

  Today I solved a problem given in Project Euler its problem no 10 and it took 7 hrs for my python program to show the result. But in that forum itself a person named lassevk posted solution for this and it took only 4 sec. And its not possible for me to post this question in that forum because its not discussion forum. So, think about this if you want to mark this question as non-constructive. marked = [0] * 2000000 value = 3 s = 2 while value < 2000000: if marked[value] == 0: s += value i = value while i < 2000000: marked[i] = 1 i += value value += 2 print s If any one understand this code please explain it simple as possible. Link to the Problem 10 question.

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• Given an even number of vertices, how to find an optimum set of pairs based on proximity?

  - by Alex Z

  The problem: We have a set of n vertices in 3D euclidean space, and there is an even number of these vertices. We want to pair them up based on their proximity. In other words, we'd like to be able to find a set of vertex pairs, where the vertices in each pair are as close as possible together. We want to minimise sacrificing the proximity between the vertices of any other pairs as much as possible in doing this. I am not looking for the most optimal solution (if it even strictly exists/can be done), just a reasonable one that can be computed relatively quickly. A relatively awful brute force approach involves choosing a vertex and looping through the rest to find its nearest neighbor and then repeating until there are none left. Of course as we near the end of the list the closest vertex could be very far away, but it is the only choice, therefore this can fail badly on the third point above.

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• Interview question: How do I detect a loop in this linked list?

  - by jjujuma

  Say you have a linked list structure in Java. It's made up of Nodes: class Node { Node next; // some user data } and each Node points to the next node, except for the last Node, which has null for next. Say there is a possibility that the list can contain a loop - i.e. the final Node, instead of having a null, has a reference to one of the nodes in the list which came before it. What's the best way of writing boolean hasLoop(Node first) which would return true if the given Node is the first of a list with a loop, and false otherwise? How could you write so that it takes a constant amount of space and a reasonable amount of time? Here's a picture of what a list with a loop looks like: Node->Node->Node->Node->Node->Node--\ \ | ----------------

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• need suggestions about content filtering project

  - by serdar

  i'm thinking of designing and implementing a content filtering software as my graduation project. i want it to be a user contributed software. i mean, users can also add/categorize websites. it should be also a web project and extensions for browsers like chrome, firefox, ie.. my question is which programming language do you suggest for this project? i know that firefox extensions are javascript based maybe you can say use .net framework 3.5 because it's better in communication with extensions. sorry for my bad english.. btw any other suggessions about project will be good.. thx a lot.

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• Algorithm for dragging objects on a fixed grid

  - by FlyingStreudel

  Hello, I am working on a program for the mapping and playing of the popular tabletop game D&D :D Right now I am working on getting the basic functionality like dragging UI elements around, snapping to the grid and checking for collisions. Right now every object when released from the mouse immediately snaps to the nearest grid point. This causes an issue when something like a player object snaps to a grid point that has a wall -or other- adjacent. So essentially when the player is dropped they wind up with some of the wall covering them. This is fine and working as intended, however the problem is that now my collision detection is tripped whenever you try to move this player because its sitting underneath a wall and because of this you cant drag the player anymore. Here is the relevant code: void UIObj_MouseMove(object sender, MouseEventArgs e) { blocked = false; if (dragging) { foreach (UIElement o in ((Floor)Parent).Children) { if (o.GetType() != GetType() && o.GetType().BaseType == typeof(UIObj) && Math.Sqrt(Math.Pow(((UIObj)o).cX - cX, 2) + Math.Pow(((UIObj)o).cY - cY, 2)) < Math.Max(r.Height + ((UIObj)o).r.Height, r.Width + ((UIObj)o).r.Width)) { double Y = e.GetPosition((Floor)Parent).Y; double X = e.GetPosition((Floor)Parent).X; Geometry newRect = new RectangleGeometry(new Rect(Margin.Left + (X - prevX), Margin.Top + (Y - prevY), Margin.Right + (X - prevX), Margin.Bottom + (Y - prevY))); GeometryHitTestParameters ghtp = new GeometryHitTestParameters(newRect); VisualTreeHelper.HitTest(o, null, new HitTestResultCallback(MyHitTestResultCallback), ghtp); } } if (!blocked) { Margin = new Thickness(Margin.Left + (e.GetPosition((Floor)Parent).X - prevX), Margin.Top + (e.GetPosition((Floor)Parent).Y - prevY), Margin.Right + (e.GetPosition((Floor)Parent).X - prevX), Margin.Bottom + (e.GetPosition((Floor)Parent).Y - prevY)); InvalidateVisual(); } prevX = e.GetPosition((Floor)Parent).X; prevY = e.GetPosition((Floor)Parent).Y; cX = Margin.Left + r.Width / 2; cY = Margin.Top + r.Height / 2; } } internal virtual void SnapToGrid() { double xPos = Margin.Left; double yPos = Margin.Top; double xMarg = xPos % ((Floor)Parent).cellDim; double yMarg = yPos % ((Floor)Parent).cellDim; if (xMarg < ((Floor)Parent).cellDim / 2) { if (yMarg < ((Floor)Parent).cellDim / 2) { Margin = new Thickness(xPos - xMarg, yPos - yMarg, xPos - xMarg + r.Width, yPos - yMarg + r.Height); } else { Margin = new Thickness(xPos - xMarg, yPos - yMarg + ((Floor)Parent).cellDim, xPos - xMarg + r.Width, yPos - yMarg + ((Floor)Parent).cellDim + r.Height); } } else { if (yMarg < ((Floor)Parent).cellDim / 2) { Margin = new Thickness(xPos - xMarg + ((Floor)Parent).cellDim, yPos - yMarg, xPos - xMarg + ((Floor)Parent).cellDim + r.Width, yPos - yMarg + r.Height); } else { Margin = new Thickness(xPos - xMarg + ((Floor)Parent).cellDim, yPos - yMarg + ((Floor)Parent).cellDim, xPos - xMarg + ((Floor)Parent).cellDim + r.Width, yPos - yMarg + ((Floor)Parent).cellDim + r.Height); } } } Essentially I am looking for a simple way to modify the existing code to allow the movement of a UI element that has another one sitting on top of it. Thanks!

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• Most Frequent 3 page sequence in a weblog

  - by Sundararajan S

  Given a web log which consists of fields 'User ' 'Page url'. We have to find out the most frequent 3-page sequence that users takes. There is a time stamp. and it is not guaranteed that the single user access will be logged sequentially it could be like user1 Page1 user2 Pagex user1 Page2 User10 Pagex user1 Page 3 her User1s page sequence is page1- page2- page 3

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• R: Forecast package: Automatic algorithm for composite model involving ETS and AR

  - by phanikishan

  Hey, I would like to write a code involving automatic selection of a best composite model using ETS as well as autoregressive models. What is the criteria I should base my selection on? Also if I'm using the auto.arima function for deducing number of AR terms and corresponding coefficients from the forecast package in R, does my input series necessarily have to be stationary? or the value for d would be automatically selected thus returning a non-stationary model? Thanks, Phani

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