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• How to prepare for a programming competition? Graphs, Stacks, Trees, oh my! [closed]

  - by Simucal

  Last semester I attended ACM's (Association for Computing Machinery) bi-annual programming competition at a local University. My University sent 2 teams of 3 people and we competed amongst other schools in the mid-west. We got our butts kicked. You are given a packet with about 11 problems (1 problem per page) and you have 4 hours to solve as many as you can. They'll run your program you submit against a set of data and your output must match theirs exactly. In fact, the judging is automated for the most part. In any case.. I went there fairly confident in my programming skills and I left there feeling drained and weak. It was a terribly humbling experience. In 4 hours my team of 3 people completed only one of the problems. The top team completed 4 of them and took 1st place. The problems they asked were like no problems I have ever had to answer before. I later learned that in order to solve them some of them effectively you have to use graphs/graph algorithms, trees, stacks. Some of them were simply "greedy" algo's. My question is, how can I better prepare for this semesters programming competition so I don't leave there feeling like a complete moron? What tips do you have for me to be able to answer these problems that involve graphs, trees, various "well known" algorithms? How can I easily identify the algorithm we should implement for a given problem? I have yet to take Algorithm Design in school so I just feel a little out of my element. Here are some examples of the questions asked at the competitions: ACM Problem Sets Update: Just wanted to update this since the latest competition is over. My team placed 1st for our small region (about 6-7 universities with between 1-5 teams each school) and ~15th for the midwest! So, it is a marked improvement over last years performance for sure. We also had no graduate students on our team and after reviewing the rules we found out that many teams had several! So, that would be a pretty big advantage in my own opinion. Problems this semester ranged from about 1-2 "easy" problems (ie bit manipulation, string manipulation) to hard (graph problems involving fairly complex math and network flow problems). We were able to solve 4 problems in our 5 hours. Just wanted to thank everyone for the resources they provided here, we used them for our weekly team practices and it definitely helped! Some quick tips that I have that aren't suggested below: When you are seated at your computer before the competition starts, quickly type out various data structures that you might need that you won't have access to in your languages libraries. I typed out a Graph data-structure complete with floyd-warshall and dijkstra's algorithm before the competition began. We ended up using it in our 2nd problem that we solved and this is the main reason why we solved this problem before anyone else in the midwest. We had it ready to go from the beginning. Similarly, type out the code to read in a file since this will be required for every problem. Save this answer "template" someplace so you can quickly copy/paste it to your IDE at the beginning of each problem. There are no rules on programming anything before the competition starts so get any boilerplate code out the way. We found it useful to have one person who is on permanent whiteboard duty. This is usually the person who is best at math and at working out solutions to get a head start on future problems you will be doing. One person is on permanent programming duty. Your fastest/most skilled "programmer" (most familiar with the language). This will save debugging time also. The last person has several roles between assessing the packet of problems for the next "easiest" problem, helping the person on the whiteboard work out solutions and helping the person programming work out bugs/issues. This person needs to be flexible and be able to switch between roles easily.

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• Physics like asteroides

  - by user2933016

  I try to make a ship that has the physic properties like asteroides. I have this for now(All in Java): Ship.class public class Ship { public static final float sMaxHealth = 0.1F; public static final float sMaxMoveVelocity = 5.0F; public static final float sMaxAngleVelocity = 20.0F; public static final float sRadius = 1.0F; public static final float sMoveDeceleration = 10.0F; public static final float sMoveAcceleration = 2.0F; public static final float sAngleDeceleration = 15.0F; public static final float sAngleAcceleration = 20.0F; private float mHealth; private float mXVelocity; private float mYVelocity; private float mAngleVelocity; private float mX; private float mY; private float mAngle; } (I let the getter and setter away for now) Controller code // Player input if(Gdx.input.isKeyPressed(Keys.UP)) { mPlayer.setXVelocity(mPlayer.getXVelocity() + (float) Math.cos(mPlayer.getAngle()) * Ship.sMoveAcceleration); mPlayer.setYVelocity(mPlayer.getYVelocity() + (float) Math.sin(mPlayer.getAngle()) * Ship.sMoveAcceleration); } if(Gdx.input.isKeyPressed(Keys.LEFT)) { mPlayer.setAngleVelocity(mPlayer.getAngleVelocity() + Ship.sAngleAcceleration * pDeltaTime); } if(Gdx.input.isKeyPressed(Keys.RIGHT)) { mPlayer.setAngleVelocity(mPlayer.getAngleVelocity() - Ship.sAngleAcceleration * pDeltaTime); } // X velocity if(mPlayer.getXVelocity() < 0) { if(-mPlayer.getXVelocity() > Ship.sMaxMoveVelocity) { mPlayer.setXVelocity(-Ship.sMaxMoveVelocity); } mPlayer.setXVelocity(mPlayer.getXVelocity() + Ship.sMoveDeceleration * pDeltaTime); if(mPlayer.getXVelocity() > 0) { mPlayer.setXVelocity(0); } } else if(mPlayer.getXVelocity() > 0) { if(mPlayer.getXVelocity() > Ship.sMaxMoveVelocity) { mPlayer.setXVelocity(Ship.sMaxMoveVelocity); } mPlayer.setXVelocity(mPlayer.getXVelocity() - Ship.sMoveDeceleration * pDeltaTime); if(mPlayer.getXVelocity() < 0) { mPlayer.setXVelocity(0); } } // Y velocity if(mPlayer.getYVelocity() < 0) { if(-mPlayer.getYVelocity() > Ship.sMaxMoveVelocity) { mPlayer.setYVelocity(-Ship.sMaxMoveVelocity); } mPlayer.setYVelocity(mPlayer.getYVelocity() + Ship.sMoveDeceleration * pDeltaTime); if(mPlayer.getYVelocity() > 0) { mPlayer.setYVelocity(0); } } else if(mPlayer.getYVelocity() > 0) { if(mPlayer.getYVelocity() > Ship.sMaxMoveVelocity) { mPlayer.setYVelocity(Ship.sMaxMoveVelocity); } mPlayer.setYVelocity(mPlayer.getYVelocity() - Ship.sMoveDeceleration * pDeltaTime); if(mPlayer.getYVelocity() < 0) { mPlayer.setYVelocity(0); } } // Angle velocity if(mPlayer.getAngleVelocity() < 0) { if(-mPlayer.getAngleVelocity() > Ship.sMaxAngleVelocity) { mPlayer.setAngleVelocity(-Ship.sMaxAngleVelocity); } mPlayer.setAngleVelocity(mPlayer.getAngleVelocity() + Ship.sAngleDeceleration * pDeltaTime); if(mPlayer.getAngleVelocity() > 0) { mPlayer.setAngleVelocity(0); } } else if(mPlayer.getAngleVelocity() > 0) { if(mPlayer.getAngleVelocity() > Ship.sMaxAngleVelocity) { mPlayer.setAngleVelocity(Ship.sMaxAngleVelocity); } mPlayer.setAngleVelocity(mPlayer.getAngleVelocity() - Ship.sAngleDeceleration * pDeltaTime); if(mPlayer.getAngleVelocity() < 0) { mPlayer.setAngleVelocity(0); } } mPlayer.setX(mPlayer.getX() + mPlayer.getXVelocity() * pDeltaTime); mPlayer.setY(mPlayer.getY() + mPlayer.getYVelocity() * pDeltaTime); mPlayer.setAngle(mPlayer.getAngle() + mPlayer.getAngleVelocity() * pDeltaTime); Why the ship does not behave like in asteroides ? What do I wrong?

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• Wikipedia A* pathfinding algorithm takes a lot of time

  - by Vee

  I've successfully implemented A* pathfinding in C# but it is very slow, and I don't understand why. I even tried not sorting the openNodes list but it's still the same. The map is 80x80, and there are 10-11 nodes. I took the pseudocode from here Wikipedia And this is my implementation: public static List<PGNode> Pathfind(PGMap mMap, PGNode mStart, PGNode mEnd) { mMap.ClearNodes(); mMap.GetTile(mStart.X, mStart.Y).Value = 0; mMap.GetTile(mEnd.X, mEnd.Y).Value = 0; List<PGNode> openNodes = new List<PGNode>(); List<PGNode> closedNodes = new List<PGNode>(); List<PGNode> solutionNodes = new List<PGNode>(); mStart.G = 0; mStart.H = GetManhattanHeuristic(mStart, mEnd); solutionNodes.Add(mStart); solutionNodes.Add(mEnd); openNodes.Add(mStart); // 1) Add the starting square (or node) to the open list. while (openNodes.Count > 0) // 2) Repeat the following: { openNodes.Sort((p1, p2) => p1.F.CompareTo(p2.F)); PGNode current = openNodes[0]; // a) We refer to this as the current square.) if (current == mEnd) { while (current != null) { solutionNodes.Add(current); current = current.Parent; } return solutionNodes; } openNodes.Remove(current); closedNodes.Add(current); // b) Switch it to the closed list. List<PGNode> neighborNodes = current.GetNeighborNodes(); double cost = 0; bool isCostBetter = false; for (int i = 0; i < neighborNodes.Count; i++) { PGNode neighbor = neighborNodes[i]; cost = current.G + 10; isCostBetter = false; if (neighbor.Passable == false || closedNodes.Contains(neighbor)) continue; // If it is not walkable or if it is on the closed list, ignore it. if (openNodes.Contains(neighbor) == false) { openNodes.Add(neighbor); // If it isn’t on the open list, add it to the open list. isCostBetter = true; } else if (cost < neighbor.G) { isCostBetter = true; } if (isCostBetter) { neighbor.Parent = current; // Make the current square the parent of this square. neighbor.G = cost; neighbor.H = GetManhattanHeuristic(current, neighbor); } } } return null; } Here's the heuristic I'm using: private static double GetManhattanHeuristic(PGNode mStart, PGNode mEnd) { return Math.Abs(mStart.X - mEnd.X) + Math.Abs(mStart.Y - mEnd.Y); } What am I doing wrong? It's an entire day I keep looking at the same code.

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• Basic collision direction detection on 2d objects

  - by Osso Buko

  I am trying to develop a platform game for Android by using ANdroid GL Engine (ANGLE). And I am having trouble with collision detection. I have two objects which is shaped as rectangular. And no change in rotation. Here is a scheme of attributes of objects. What i am trying to do is when objects collide they block each other's movement on that direction. Every object has 4 boolean (bTop, bBottom, bRight, bLeft). For example when bBottom is true object can't advance on that direction. I came up with a solution but it seems it only works on one dimensional. Bottom and top or right and left. public void collisionPlatform (MyObject a, MyObject b) { // first obj is player and second is a wall or a platform Vector p1 = a.mPosition; // p1 = middle point of first object Vector d1 = a.mPosition2; // width(mX) and height of first object Vector mSpeed1 = a.mSpeed; // speed vector of first object Vector p2 = b.mPosition; // p1 = middle point of second object Vector d2 = b.mPosition2; // width(mX) and height of second object Vector mSpeed2 = b.mSpeed; // speed vector of second object float xDist, yDist; // distant between middle of two object float width , height; // this is average of two objects measurements width=(width1+width2)/2 xDist=(p1.mX - p2.mX); // calculate distance // if positive first object is at the right yDist=(p1.mY - p2.mY); // if positive first object is below width = d1.mX + d2.mX; // average measurements calculate height = d1.mY + d2.mY; width/=2; height/=2; if (Math.abs(xDist) < width && Math.abs(yDist) < height) { // Two object is collided if(p1.mY>p2.mY) { // first object is below second one a.bTop = true; if(a.mSpeed.mY<0) a.mSpeed.mY=0; b.bBottom = true; if(b.mSpeed.mY>0) b.mSpeed.mY=0; } else { a.bBottom = true; if(a.mSpeed.mY>0) a.mSpeed.mY=0; b.bTop = true; if(b.mSpeed.mY<0) b.mSpeed.mY=0; } } As seen in my code it simply will not work. when object comes from right or left it doesn't work. I tried couple of ways other than this one but none worked. I am guessing right method will include mSpeed vector. But I have no idea how to do it. I really appreciate if you could help. Sorry for my bad english.

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• Dynamically load and call delegates based on source data

  - by makerofthings7

  Assume I have a stream of records that need to have some computation. Records will have a combination of these functions run Sum, Aggregate, Sum over the last 90 seconds, or ignore. A data record looks like this: Date;Data;ID Question Assuming that ID is an int of some kind, and that int corresponds to a matrix of some delegates to run, how should I use C# to dynamically build that launch map? I'm sure this idea exists... it is used in Windows Forms which has many delegates/events, most of which will never actually be invoked in a real application. The sample below includes a few delegates I want to run (sum, count, and print) but I don't know how to make the quantity of delegates fire based on the source data. (say print the evens, and sum the odds in this sample) using System; using System.Threading; using System.Collections.Generic; internal static class TestThreadpool { delegate int TestDelegate(int parameter); private static void Main() { try { // this approach works is void is returned. //ThreadPool.QueueUserWorkItem(new WaitCallback(PrintOut), "Hello"); int c = 0; int w = 0; ThreadPool.GetMaxThreads(out w, out c); bool rrr =ThreadPool.SetMinThreads(w, c); Console.WriteLine(rrr); // perhaps the above needs time to set up6 Thread.Sleep(1000); DateTime ttt = DateTime.UtcNow; TestDelegate d = new TestDelegate(PrintOut); List<IAsyncResult> arDict = new List<IAsyncResult>(); int count = 1000000; for (int i = 0; i < count; i++) { IAsyncResult ar = d.BeginInvoke(i, new AsyncCallback(Callback), d); arDict.Add(ar); } for (int i = 0; i < count; i++) { int result = d.EndInvoke(arDict[i]); } // Give the callback time to execute - otherwise the app // may terminate before it is called //Thread.Sleep(1000); var res = DateTime.UtcNow - ttt; Console.WriteLine("Main program done----- Total time --> " + res.TotalMilliseconds); } catch (Exception e) { Console.WriteLine(e); } Console.ReadKey(true); } static int PrintOut(int parameter) { // Console.WriteLine(Thread.CurrentThread.ManagedThreadId + " Delegate PRINTOUT waited and printed this:"+parameter); var tmp = parameter * parameter; return tmp; } static int Sum(int parameter) { Thread.Sleep(5000); // Pretend to do some math... maybe save a summary to disk on a separate thread return parameter; } static int Count(int parameter) { Thread.Sleep(5000); // Pretend to do some math... maybe save a summary to disk on a separate thread return parameter; } static void Callback(IAsyncResult ar) { TestDelegate d = (TestDelegate)ar.AsyncState; //Console.WriteLine("Callback is delayed and returned") ;//d.EndInvoke(ar)); } }

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• WPF / C#: Transforming coordinates from an image control to the image source

  - by Gabriel

  I'm trying to learn WPF, so here's a simple question, I hope: I have a window that contains an Image element bound to a separate data object with user-configurable Stretch property <Image Name="imageCtrl" Source="{Binding MyImage}" Stretch="{Binding ImageStretch}" /> When the user moves the mouse over the image, I would like to determine the coordinates of the mouse with respect to the original image (before stretching/cropping that occurs when it is displayed in the control), and then do something with those coordinates (update the image). I know I can add an event-handler to the MouseMove event over the Image control, but I'm not sure how best to transform the coordinates: void imageCtrl_MouseMove(object sender, MouseEventArgs e) { Point locationInControl = e.GetPosition(imageCtrl); Point locationInImage = ??? updateImage(locationInImage); } Now I know I could compare the size of Source to the ActualSize of the control, and then switch on imageCtrl.Stretch to compute the scalars and offsets on X and Y, and do the transform myself. But WPF has all the information already, and this seems like functionality that might be built-in to the WPF libraries somewhere. So I'm wondering: is there a short and sweet solution? Or do I need to write this myself? EDIT I'm appending my current, not-so-short-and-sweet solution. Its not that bad, but I'd be somewhat suprised if WPF didn't provide this functionality automatically: Point ImgControlCoordsToPixelCoords(Point locInCtrl, double imgCtrlActualWidth, double imgCtrlActualHeight) { if (ImageStretch == Stretch.None) return locInCtrl; Size renderSize = new Size(imgCtrlActualWidth, imgCtrlActualHeight); Size sourceSize = bitmap.Size; double xZoom = renderSize.Width / sourceSize.Width; double yZoom = renderSize.Height / sourceSize.Height; if (ImageStretch == Stretch.Fill) return new Point(locInCtrl.X / xZoom, locInCtrl.Y / yZoom); double zoom; if (ImageStretch == Stretch.Uniform) zoom = Math.Min(xZoom, yZoom); else // (imageCtrl.Stretch == Stretch.UniformToFill) zoom = Math.Max(xZoom, yZoom); return new Point(locInCtrl.X / zoom, locInCtrl.Y / zoom); }

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• WPF 4.0 Custom panel won't show dynamically added controls in VS 2010 Designer

  - by Matt Ruwe

  I have a custom panel control that I'm trying to dynamically add controls within. When I run the application the static and dynamically added controls show up perfectly, but the dynamic controls do not appear within the visual studio designer. Only the controls placed declaratively in the XAML appear. I'm currently adding the dynamic control in the CreateUIElementCollection override, but I've also tried this in the constructor without success. Public Class CustomPanel1 Inherits Panel Public Sub New() End Sub Protected Overrides Function MeasureOverride(ByVal availableSize As System.Windows.Size) As System.Windows.Size Dim returnValue As New Size(0, 0) For Each child As UIElement In Children child.Measure(availableSize) returnValue.Width = Math.Max(returnValue.Width, child.DesiredSize.Width) returnValue.Height = Math.Max(returnValue.Height, child.DesiredSize.Height) Next returnValue.Width = If(Double.IsPositiveInfinity(availableSize.Width), returnValue.Width, availableSize.Width) returnValue.Height = If(Double.IsPositiveInfinity(availableSize.Height), returnValue.Height, availableSize.Height) Return returnValue End Function Protected Overrides Function ArrangeOverride(ByVal finalSize As System.Windows.Size) As System.Windows.Size Dim currentHeight As Integer For Each child As UIElement In Children child.Arrange(New Rect(0, currentHeight, child.DesiredSize.Width, child.DesiredSize.Height)) currentHeight += child.DesiredSize.Height Next Return finalSize End Function Protected Overrides Function CreateUIElementCollection(ByVal logicalParent As System.Windows.FrameworkElement) As System.Windows.Controls.UIElementCollection Dim returnValue As UIElementCollection = MyBase.CreateUIElementCollection(logicalParent) returnValue.Add(New TextBlock With {.Text = "Hello, World!"}) Return returnValue End Function Protected Overrides Sub OnPropertyChanged(ByVal e As System.Windows.DependencyPropertyChangedEventArgs) MyBase.OnPropertyChanged(e) End Sub End Class And my usage of this custom panel <Window x:Class="MainWindow" xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation" xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml" xmlns:local="clr-namespace:CustomPanel" Title="MainWindow" Height="364" Width="434"> <local:CustomPanel1> <CheckBox /> <RadioButton /> </local:CustomPanel1> </Window>

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• jQuery $.ajax Not Working in IE8 but it works on FireFox & Chrome

  - by Sam3k

  I have the following ajax call which works perfectly in Firefox and Chrome but not IE: function getAJAXdates( startDate, numberOfNights, opts ) { var month = startDate.getMonth() + 1; var day = startDate.getDate(); var year = startDate.getFullYear(); var d = new Date(); var randNum = Math.floor(Math.random()*100000000); $.ajax({ type : "GET", dataType : "json", url : "/availability/ajax/bookings?rand="+randNum, cache : false, data : 'month='+month+'&day='+day+'&year='+year+'&nights='+numberOfNights, contentType : 'application/json; charset=utf8', success : function(data) { console.log('@data: '+data); insertCellData(data, opts, startDate); }, error:function(xhr, status, errorThrown) { console.log('@Error: '+errorThrown); console.log('@Status: '+status); console.log('@Status Text: '+xhr.statusText); } }); } I know for a fact that all the variables are passing the right content and $.ajax is indeed passing all the paramater/values. This is what I get on error: LOG: @Error: undefined LOG: @Status: parsererror LOG: @Status Text: OK I'm aware of the cache issue on IE and implemented a random paramater to clear it up. Finally these are the headers that are sent back from the backend: header('Content-Type: application/json; charset=utf8'); header("Cache-Control: no-cache"); header("Expires: 0"); header('Access-Control-Max-Age: 3628800'); header('Access-Control-Allow-Methods: GET, POST, PUT, DELETE');

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• TeX Font Mapping

  - by reprogrammer

  I am using a package written on top of XeLaTeX. This package uses fontspec to specify fonts for different parts of your text: latin, non-latin, math mode, ... The package comes with several sample files. I was able to xelatex most of them that depend on regular ttf or otf files. However, one of them tries to set the font of digits in math mode to some font, say "NonLatin Digits". But, the font doesn't seem to be a regular font. There are two files in the same directory called "nonlatindigits.map" and "nonlatindigits.tec". TECkit uses these mapping files to generate TeX fonts. However, for some reason it fails to create the files, and xelatex issues the following error message. kpathsea: Invalid fontname `NonLatin Digits', contains ' ' ! Font \zf@basefont="NonLatin Digits" at 10.0pt not loadable: Metric (TFM) file or installed font not found. The kpathsea program complains about the whitespace, but removing the whitespace does solve the problem with loading the TFM file. Any clues what I am doing wrong?

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• FullCalendar and events: function

  - by Ernest

  I am trying to display my events from a MySQL database. I'm using the events function. My XML file being returned is pretty basic. I've looked at all of the FullCalendar questions and most of them talk about JSON and point to the documentation for JSON. I can't use JSON. I have to go XML. Can you tell me where I'm off. Here is a sample of what my xml looks like: Grow Your Business on the Web 2010-06-05T9:30 2010-06-05T12:30 O The whole file is prefaced with a tag and closed with a tag. My jquery is as follows: $(document).ready(function() { $('#calendar').fullCalendar({ height: 550, theme: true, header: { left: 'prev,next today', center: 'title', right: 'month,agendaWeek,agendaDay' }, editable: true, events: function(start, end, callback) { $.ajax({ url: 'ncludeFiles/sbdp-cal-xml.php', dataType: 'xml', data: { // our hypothetical feed requires UNIX timestamps start: Math.round(start.getTime() / 1000), end: Math.round(end.getTime() / 1000) }, success: function(doc) { var events = []; $(doc).find('event').each(function() { events.push({ title: $(this).attr('title'), start: $(this).attr('start'), end: $(this).attr('end'), className: $(this).attr('className'), url: $(this).attr('url') }); }); callback(events); } }); } }); }); I'd appreciate any help you could give me. Thanks!

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• How to make Chrome redraw SVG dynamically added content?

  - by Adrian

  I've dynamacally added the circle elements to the svg displayed in a iFrame. Chrome isnt showing the new elements, not tried FF yet. Is there somekind of redraw/refresh I need to call? The first circle is actually in the svg document, the rest come from script. <iframe id="svgFrame" src="xmlfile1.svg" width="300" height="300"> <svg xmlns="http://www.w3.org/2000/svg" id="SVG1" width="200" height="200"> <circle cx="20" cy="20" r="5"/> <circle cx="165" cy="80" r="32"/> <circle cx="15" cy="38" r="32"/> <circle cx="140" cy="39" r="30"/> <circle cx="178" cy="32" r="22"/> ...etc <circle cx="166" cy="130" r="16"/> </svg> </iframe> The javascript which creates the elements: function RandomNumber(min, max) { var r; r = Math.floor(Math.random() * (max - min + 1)) + min; return r; } var svg = document.getElementById("svgFrame").contentDocument; for (var i = 0; i < 99; i++) { var n = svg.createElement("circle"); n.setAttribute("cx" , RandomNumber( 0 , 200) ); n.setAttribute("cy" , RandomNumber(0, 200) ); n.setAttribute("r" , RandomNumber(5, 35) ); svg.documentElement.appendChild(n); }

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• Crystal Reports Programmatic Image Resizing... Scale?

  - by C. Griffin

  I'm working with a Crystal Reports object in Visual Studio 2008 (C#). The report is building fine and the data is binding correctly. However, when I try to resize an IBlobFieldObject from within the source, the scale is getting skewed. Two notes about this scenario. Source image is 1024x768, my max width and height are 720x576. My math should be correct that my new image size will be 720x540 (to fit within the max width and height guidelines). The ratio is wrong when I do this though: img = Image.FromFile(path); newWidth = img.Size.Width; newHeight = img.Size.Height; if ((img.Size.Width > 720) || (img.Size.Height > 576)) { double ratio = Convert.ToDouble(img.Size.Width) / Convert.ToDouble(img.Size.Height); if (ratio > 1.25) // Adjust width to 720, height will fall within range { newWidth = 720; newHeight = Convert.ToInt32(Convert.ToDouble(img.Size.Height) * 720.0 / Convert.ToDouble(img.Size.Width)); } else // Adjust height to 576, width will fall within range { newHeight = 576; newWidth = Convert.ToInt32(Convert.ToDouble(img.Size.Width) * 576.0 / Convert.ToDouble(img.Size.Height)); } imgRpt.Section3.ReportObjects["image"].Height = newHeight; imgRpt.Section3.ReportObjects["image"].Width = newWidth; } I've stepped through the code to make sure that the values are correct from the math, and I've even saved the image file out to make sure that the aspect ratio is correct (it was). No matter what I try though, the image is squashed--almost as if the Scale values are off in the Crystal Reports designer (they're not). Thanks in advance for any help!

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• Transforming coordinates from an image control to the image source in WPF

  - by Gabriel

  I'm trying to learn WPF, so here's a simple question, I hope: I have a window that contains an Image element bound to a separate data object with user-configurable Stretch property <Image Name="imageCtrl" Source="{Binding MyImage}" Stretch="{Binding ImageStretch}" /> When the user moves the mouse over the image, I would like to determine the coordinates of the mouse with respect to the original image (before stretching/cropping that occurs when it is displayed in the control), and then do something with those coordinates (update the image). I know I can add an event-handler to the MouseMove event over the Image control, but I'm not sure how best to transform the coordinates: void imageCtrl_MouseMove(object sender, MouseEventArgs e) { Point locationInControl = e.GetPosition(imageCtrl); Point locationInImage = ??? updateImage(locationInImage); } Now I know I could compare the size of Source to the ActualSize of the control, and then switch on imageCtrl.Stretch to compute the scalars and offsets on X and Y, and do the transform myself. But WPF has all the information already, and this seems like functionality that might be built-in to the WPF libraries somewhere. So I'm wondering: is there a short and sweet solution? Or do I need to write this myself? EDIT I'm appending my current, not-so-short-and-sweet solution. Its not that bad, but I'd be somewhat suprised if WPF didn't provide this functionality automatically: Point ImgControlCoordsToPixelCoords(Point locInCtrl, double imgCtrlActualWidth, double imgCtrlActualHeight) { if (ImageStretch == Stretch.None) return locInCtrl; Size renderSize = new Size(imgCtrlActualWidth, imgCtrlActualHeight); Size sourceSize = bitmap.Size; double xZoom = renderSize.Width / sourceSize.Width; double yZoom = renderSize.Height / sourceSize.Height; if (ImageStretch == Stretch.Fill) return new Point(locInCtrl.X / xZoom, locInCtrl.Y / yZoom); double zoom; if (ImageStretch == Stretch.Uniform) zoom = Math.Min(xZoom, yZoom); else // (imageCtrl.Stretch == Stretch.UniformToFill) zoom = Math.Max(xZoom, yZoom); return new Point(locInCtrl.X / zoom, locInCtrl.Y / zoom); }

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• "Permission denied to access property 'href' from a non-chrome context" in JavaScript and OpenLayers

  - by Mark Iliffe

  This is really two questions one leading into the other. Firstly what does 'Permission denied to access property 'href' from a non-chrome context' actually mean? Secondly I am using overlays in OpenLayers and wish to change the opacity of said layers, this is where this error is being thrown the code of which is here... <input id='opacity' value="1.0" onChange="changeOpacity()"> Of which changeOpacity() is the following function... function changeOpacity() { var newOpacity = parseFloat(OpenLayers.Util.getElement('opacity').value); newOpacity = Math.min(1.0, Math.max(0.1, newOpacity)); OpenLayers.Util.getElement('opacity').value = newOpacity; for (var i=0; i<images.length; i++) { layers[images[i]].setOpacity(newOpacity); } } which throws the error at "var href = originalElement.href;" here... function mD(e) { //what is originalElement/srcElement/originalTarget? var originalElement = e.srcElement || e.originalTarget; var href = originalElement.href; if (originalElement.nodeName == "A" && href.match("http://www.openstreetmap.org/browse/")) { href = href.replace('http://www.openstreetmap.org/browse/','http://www.openstreetmap.org/api/0.6/'); if (gml) { map.removeLayer(gml); } //$("status").innerHTML = 'loading'; } gml = new OpenLayers.Layer.GML("OSM", href, {format: OpenLayers.Format.OSM}); map.addLayer(gml); gml.preFeatureInsert = style_osm_feature; var sf = new OpenLayers.Control.SelectFeature(gml, {'onSelect': on_feature_hover}); map.addControl(sf); sf.activate(); return false; } } Any help/ideas is great appreciated! I am using firefox 3.5.9 and firebug 1.5.4

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• Java random values and duplicates

  - by f-Prime

  I have an array (cards) of 52 cards (13x4), and another array (cardsOut) of 25 cards (5x5). I want to copy elements from the 52 cards into the 25 card array by random. Also, I dont want any duplicates in the 5x5 array. So here's what I have: double row=Math.random() *13; double column=Math.random() *4; boolean[][] duplicates=new boolean[13][4]; pokerGame[][] cardsOut = new pokerGame[5][5]; for (int i=0;i<5;i++) for (int j=0;j<5;j++){ if(duplicates[(int)row][(int)column]==false){ cardsOut[i][j]=cards[(int)row][(int)column]; duplicates[(int)row][(int)column]=true; } } 2 problems in this code. First, the random values for row and column are only generated once, so the same value is copied into the 5x5 array every time. Since the same values are being copied every time, I'm not sure if my duplicate checker is very effective, or if it works at all. How do I fix this?

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• Saturated addition of two signed Java 'long' values

  - by finnw

  How can one add two long values (call them x and y) in Java so that if the result overflows then it is clamped to the range Long.MIN_VALUE..Long.MAX_VALUE? For adding ints one can perform the arithmetic in long precision and cast the result back to an int, e.g.: int saturatedAdd(int x, int y) { long sum = (long) x + (long) y; long clampedSum = Math.max((long) Integer.MIN_VALUE, Math.min(sum, (long) Integer.MAX_VALUE)); return (int) clampedSum; } or import com.google.common.primitives.Ints; int saturatedAdd(int x, int y) { long sum = (long) x + (long) y; return Ints.saturatedCast(sum); } but in the case of long there is no larger primitive type that can hold the intermediate (unclamped) sum. Since this is Java, I cannot use inline assembly (in particular SSE's saturated add instructions.) It can be implemented using BigInteger, e.g. static final BigInteger bigMin = BigInteger.valueOf(Long.MIN_VALUE); static final BigInteger bigMax = BigInteger.valueOf(Long.MAX_VALUE); long saturatedAdd(long x, long y) { BigInteger sum = BigInteger.valueOf(x).add(BigInteger.valueOf(y)); return bigMin.max(sum).min(bigMax).longValue(); } however performance is important so this method is not ideal (though useful for testing.) I don't know whether avoiding branching can significantly affect performance in Java. I assume it can, but I would like to benchmark methods both with and without branching. Related: http://stackoverflow.com/questions/121240/saturating-addition-in-c

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• Computer science textbooks

  - by Barrett Conrad

  I would like to try the book question a little bit differently. My goal is to know what the community thinks are the quintessential computer science textbooks. <beginsadstory>I lost all of my computer science and math books from college in Hurricane Katrina in 2005. I greatly miss having my familiar tomes to refer to when topics and problems come up, so I am looking to rebuild my library.<endsadstory> What are your recommendations for the best examples of academic caliber books for the field of computer science and its associated mathematics? I am looking for books on subjects like computational theory, programming languages, compilers, operating systems, algorithms and so on. Don't limit your suggestions to your textbooks only. If there is a book you have read that covers computer science or a related math in a formal way, but is not strictly a textbook, I would be love to hear about them as well. Finally, for the sake of creating a good reference for all of us, may I suggest posting one book per answer so they can be rated individually.

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• Fuzzy Date algorithm in Objective-C

  - by Brock Woolf

  I would like to write a fuzzy date method for calculating dates in Objective-C for iPhone. There is a popular explanation here: http://stackoverflow.com/questions/11/how-do-i-calculate-relative-time However it contains missing arguments. How could this be used in Objective-C?. Thanks. const int SECOND = 1; const int MINUTE = 60 * SECOND; const int HOUR = 60 * MINUTE; const int DAY = 24 * HOUR; const int MONTH = 30 * DAY; if (delta < 1 * MINUTE) { return ts.Seconds == 1 ? "one second ago" : ts.Seconds + " seconds ago"; } if (delta < 2 * MINUTE) { return "a minute ago"; } if (delta < 45 * MINUTE) { return ts.Minutes + " minutes ago"; } if (delta < 90 * MINUTE) { return "an hour ago"; } if (delta < 24 * HOUR) { return ts.Hours + " hours ago"; } if (delta < 48 * HOUR) { return "yesterday"; } if (delta < 30 * DAY) { return ts.Days + " days ago"; } if (delta < 12 * MONTH) { int months = Convert.ToInt32(Math.Floor((double)ts.Days / 30)); return months <= 1 ? "one month ago" : months + " months ago"; } else { int years = Convert.ToInt32(Math.Floor((double)ts.Days / 365)); return years <= 1 ? "one year ago" : years + " years ago"; }

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• How can I make an AdvancedDataGrid re-display its labels when the results of the labelFunction chang

  - by Chris R

  I have an AdvancedDataGrid with a custom label function whose value can change based on other form status (specifically, there's a drop down to choose the time display format for some columns). Right now, I have this labelFunction: internal function formatColumnTime(item: Object, column: AdvancedDataGridColumn): String { var seconds: Number = item[column.dataField]; return timeFormat.selectedItem.labelFunction(seconds); } internal function formatTimeAsInterval(time: Number): String { if (isNaN(time)) return ""; var integerTime: int = Math.round(time); var seconds: int = integerTime % 60; integerTime = integerTime / 60; var minutes: int = integerTime % 60; var hours: int = integerTime / 60; return printf("%02d:%02d:%02d", hours, minutes, seconds); } internal function formatTimeAsFractions(time: Number): String { if (isNaN(time)) return ""; var hours: Number = time / 3600.0; return new String(Math.round(hours * 100) / 100); } ... and the timeFormat object is a combo box with items whose labelFunction attributes are formatTimeAsFractions and formatTimeAsInterval. The columns that have time formats have formatColumnTime as their labelFunction value, because extracting the seconds in that function and passing it in to the formatters made for a more testable app (IMHO). So, when the timeFormat.selectedItem value changes, I want to force my grid to re-calculate the labels of these colums. What method must I call on it? invalidateProperties() didn't work, so that's out.

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• Rendering LaTeX on third-party websites

  - by A. Rex

  There are some sites on the web that render LaTeX into some more readable form, such as Wikipedia, some Wordpress blogs, and MathOverflow. They may use images, MathML, jsMath, or something like that. There are other sites on the web where LaTeX appears inline and is not rendered, such as the arXiv, various math forums, or my email. In fact, it is quite common to see an arXiv paper's abstract with raw LaTeX in it, e.g. this paper. Is there a plugin available for Firefox, or would it be possible to write one, that renders LaTeX within pages that do not provide a rendering mechanism themselves? Some notes: It may be impossible to render some of the code, because authors often copy-paste code directly from their source TeX files, which may contain things like "\cite{foo}" or undefined commands. These should be left alone. This question is a repost of a question from MathOverflow that was closed for not being related to math. I program a lot, but Javascript is not my specialty, so comments along the lines of "look at this library" are not particularly helpful to me (but may be to others).

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• Use jquery to create a multidimensional array

  - by Simon M White

  I'd like to use jquery and a multidemensional array to show a random quote plus the name of the individual who wrote it as a separate item. I'll then be able to use css to style them differently. The quote will change upon page refresh. So far i have this code which combines the quote and the name and person who wrote it: $(document).ready(function(){ var myQuotes = new Array(); myQuotes[0] = "Lorem ipsum dolor sit amet, consectetur adipiscing elit. Donec in tortor mauris. Peter Jones, Dragons Den"; myQuotes[1] = "Curabitur interdum, nibh et fringilla facilisis, lacus ipsum pulvinar mauris, eu facilisis justo arcu eget diam. Duis id sagittis elit. Theo Pathetis, Dragons Den"; myQuotes[2] = "Vivamus purus purus, tincidunt et porttitor et, euismod sit amet urna. Etiam sollicitudin eros nec metus pretium scelerisque. James Caan, Dragons Den"; var myRandom = Math.floor(Math.random()*myQuotes.length); $('.quote-holder blockquote span').html(myQuotes[myRandom]); }); any help would be greatly appreciated.

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• define javascript functions on iframe facebook app inside <fb:serverfbml> tag

  - by user233486

  Hi all, How we can define JS function on inside ? I tried to load file javascript on the end tag , but I still can't call the function from javascript file. Here the FBML tag <fb:serverfbml> <script type="text/fbml"> <fb:fbml> <a href="#" id="this" onclick="do_colors(this); return false">Hello World!</a> <script src="http://absolute.path.to/your/javascript/file.js"></script> </fb:fbml> </script> </fb:serverfbml> And here the javacript function on file.js function random_int(lo, hi) { return Math.floor((Math.random() * (hi - lo)) + lo) } function do_colors(obj) { var r = random_int(0, 255), b = random_int(0, 255), g = random_int(0, 255); obj.setStyle({background: 'rgb('+[r, g, b].join(',')+')', color: 'rgb('+[r<128?r+128:r-128, g<128?g+128:g-128, b<128?b+128:b-128].join(',')+')'}); } I use rails and facebooker to develop the application Any idea or suggestion for define javascript functions? Thanks,

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• What is the best way to parse python script file in C/C++ code

  - by alexpov

  I am embedding python in C/C++ program. What I am trying to do is to parse the python script file from the C/C++ program, break the file to "blocks" so that each "block" is an a valid command in python code. Each block I need to put into std::string. For example: #PythonScript.py import math print "Hello Python" i = 0; while (i < 10): print "i = " , i; i = i + 1; print "GoodBye Python" In this script are 5 different "blocks": the first one is "import math;" the second is "print "Hello Python;" the third is "i = 0;" and the fourth is while (i < 10):\n\tprint "i = " , i;\n\ti = i + 1; My knowledge in python is very basic and I am not familiar with the python code syntax. What is the best way to do this, is there any Python C/C++ API function that supports this? why i need it - for GUI purpose. My program , which is writen in C, uses python to make some calculations. I run from C code , using python C API , python script and what i need is a way to capture python's output in my program. I catch it and evrything is ok, the problem is when the script involves user input. What happens is that i capture python's output after the script is finished , therefore, when there is an input command in the script i get a black screen .... i need to get all the printings before the input command. The first solution i tried is to parss the script to valid commands and run each comand, one after the other , seperatly .... for this i need to pars the script and deside what is a command and what is not ... The question is : what is the best way to do this and if there is somthing that allready does ?

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• What are some funny loading statements to keep users amused?

  - by Oli

  Nobody likes waiting but unfortunately in the Ajax application I'm working on at the moment, there is one fair-sized pause (1-2 seconds a go) that users have to undergo each and every time they want to load up a chunk of data. I've tried to make the load as interactive as possible. There's an animated GIF alongside a very plain, very dull "Loading..." message. So I thought it might be quite fun to come up with a batch of 50-or-so funny-looking messages and pick from them randomly so the user never knows what they're going to see. The time they would have spent growing impatient is fruitfully used. Here's what I've come up with so far, just to give you an idea. var randomLoadingMessage = function() { var lines = new Array( "Locating the required gigapixels to render...", "Spinning up the hamster...", "Shovelling coal into the server...", "Programming the flux capacitor" ); return lines[Math.round(Math.random()*(lines.length-1))]; } (Yes -- I know some of those are pretty lame -- That's why I'm here :) The funniest I see today will get the prestigious "Accepted Answer" award. Others get votes for participation. Enjoy!!

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• Project Euler 7 Scala Problem

  - by Nishu

  I was trying to solve Project Euler problem number 7 using scala 2.8 First solution implemented by me takes ~8 seconds def problem_7:Int = { var num = 17; var primes = new ArrayBuffer[Int](); primes += 2 primes += 3 primes += 5 primes += 7 primes += 11 primes += 13 while (primes.size < 10001){ if (isPrime(num, primes)) primes += num if (isPrime(num+2, primes)) primes += num+2 num += 6 } return primes.last; } def isPrime(num:Int, primes:ArrayBuffer[Int]):Boolean = { // if n == 2 return false; // if n == 3 return false; var r = Math.sqrt(num) for (i <- primes){ if(i <= r ){ if (num % i == 0) return false; } } return true; } Later I tried the same problem without storing prime numbers in array buffer. This take .118 seconds. def problem_7_alt:Int = { var limit = 10001; var count = 6; var num:Int = 17; while(count < limit){ if (isPrime2(num)) count += 1; if (isPrime2(num+2)) count += 1; num += 6; } return num; } def isPrime2(n:Int):Boolean = { // if n == 2 return false; // if n == 3 return false; var r = Math.sqrt(n) var f = 5; while (f <= r){ if (n % f == 0) { return false; } else if (n % (f+2) == 0) { return false; } f += 6; } return true; } I tried using various mutable array/list implementations in Scala but was not able to make solution one faster. I do not think that storing Int in a array of size 10001 can make program slow. Is there some better way to use lists/arrays in scala?

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