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  • Calculate the number of ways to roll a certain number

    - by helloworld
    I'm a high school Computer Science student, and today I was given a problem to: Program Description: There is a belief among dice players that in throwing three dice a ten is easier to get than a nine. Can you write a program that proves or disproves this belief? Have the computer compute all the possible ways three dice can be thrown: 1 + 1 + 1, 1 + 1 + 2, 1 + 1 + 3, etc. Add up each of these possibilities and see how many give nine as the result and how many give ten. If more give ten, then the belief is proven. I quickly worked out a brute force solution, as such int sum,tens,nines; tens=nines=0; for(int i=1;i<=6;i++){ for(int j=1;j<=6;j++){ for(int k=1;k<=6;k++){ sum=i+j+k; //Ternary operators are fun! tens+=((sum==10)?1:0); nines+=((sum==9)?1:0); } } } System.out.println("There are "+tens+" ways to roll a 10"); System.out.println("There are "+nines+" ways to roll a 9"); Which works just fine, and a brute force solution is what the teacher wanted us to do. However, it doesn't scale, and I am trying to find a way to make an algorithm that can calculate the number of ways to roll n dice to get a specific number. Therefore, I started generating the number of ways to get each sum with n dice. With 1 die, there is obviously 1 solution for each. I then calculated, through brute force, the combinations with 2 and 3 dice. These are for two: There are 1 ways to roll a 2 There are 2 ways to roll a 3 There are 3 ways to roll a 4 There are 4 ways to roll a 5 There are 5 ways to roll a 6 There are 6 ways to roll a 7 There are 5 ways to roll a 8 There are 4 ways to roll a 9 There are 3 ways to roll a 10 There are 2 ways to roll a 11 There are 1 ways to roll a 12 Which looks straightforward enough; it can be calculated with a simple linear absolute value function. But then things start getting trickier. With 3: There are 1 ways to roll a 3 There are 3 ways to roll a 4 There are 6 ways to roll a 5 There are 10 ways to roll a 6 There are 15 ways to roll a 7 There are 21 ways to roll a 8 There are 25 ways to roll a 9 There are 27 ways to roll a 10 There are 27 ways to roll a 11 There are 25 ways to roll a 12 There are 21 ways to roll a 13 There are 15 ways to roll a 14 There are 10 ways to roll a 15 There are 6 ways to roll a 16 There are 3 ways to roll a 17 There are 1 ways to roll a 18 So I look at that, and I think: Cool, Triangular numbers! However, then I notice those pesky 25s and 27s. So it's obviously not triangular numbers, but still some polynomial expansion, since it's symmetric. So I take to Google, and I come across this page that goes into some detail about how to do this with math. It is fairly easy(albeit long) to find this using repeated derivatives or expansion, but it would be much harder to program that for me. I didn't quite understand the second and third answers, since I have never encountered that notation or those concepts in my math studies before. Could someone please explain how I could write a program to do this, or explain the solutions given on that page, for my own understanding of combinatorics? EDIT: I'm looking for a mathematical way to solve this, that gives an exact theoretical number, not by simulating dice

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  • Compare class objects

    - by reto
    I have to compare a class object against a list of pre defined classes. Is it safe to use == or should I use equals()? if (klass == KlassA.class) { } else if (klass == KlassB.class) { } else if (klass == KlassC.class) { } else { } Note: I cannot use instanceof, I don't have an object, I just have the class object. I (mis)use it like an enum in this situation! Thanks!

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  • Why new String(bytes, enc).getBytes(enc) does not return the original byte array?

    - by Bozho
    I made the following "simulation": byte[] b = new byte[256]; for (int i = 0; i < 256; i ++) { b[i] = (byte) (i - 128); } byte[] transformed = new String(b, "cp1251").getBytes("cp1251"); for (int i = 0; i < b.length; i ++) { if (b[i] != transformed[i]) { System.out.println("Wrong : " + i); } } For cp1251 this outputs only one wrong byte - at position 23. For KOI8-R - all fine. For cp1252 - 4 or 5 differences. What is the reason for this and how can this be overcome? I know it is wrong to represent byte arrays as strings in whatever encoding, but it is a requirement of the protocol of a payment provider, so I don't have a choice. Update: representing it in ISO-8859-1 works, and I'll use it for the byte[] part, and cp1251 for the textual part, so the question remains only out of curiousity

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  • automatically minimized chat tabs

    - by Xiang Ubao
    now I have a very urgent matter, ask for your help.Because we must call fu.init in hideFlashCallback to pause our game, When the user is in the another page to open chat tabs to our game, the game will pause automatically. Is there a method like FB API or something at the beginning of the loading game, automatically minimized chat tabs, so as to solve our problems.Hope you reply to us, help us to solve the problem. Thanks a million.

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  • Loading data from file to Vector structure

    - by owca
    I'm trying to parse through fixed-width formatted file extracting x,y values of points from it, and then storing them in int[] array inside a Vector. Text file looks as follows : 0006 0015 0125 0047 0250 0131 That's the code : Vector<int[]> vc = new Vector<int[]>(); try { BufferedReader file = new BufferedReader(new FileReader("myfile.txt")); String s; int[] vec = new int[2]; while ((s = file.readLine()) != null) { vec[0] = Integer.parseInt(s.substring(0, 4).trim()); vec[1] = Integer.parseInt(s.substring(5, 8).trim()); vc.add(vec); } file.close(); } catch (IOException e) { } for(int i=0; i<vc.size(); i++){ for(int j=0; j<2; j++){ System.out.println(vc.elementAt(i)[j]); } } But the output shows only last line. 250 131 250 131 250 131 Should I somehow use Vector.nextElement() here to get all my data ?

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  • when get pagecontent from URL the connect alway return nopermistion ?

    - by tiendv
    I have a methor to return pagecontent of link but when it run, alway return "Do not perrmisson ", plesea check it here is code to return string pagecontent public static String getPageContent(String targetURL) throws Exception { Hashtable contentHash = new Hashtable(); URL url; URLConnection conn; // The data streams used to read from and write to the URL connection. DataOutputStream out; DataInputStream in; // String returned as the result . String returnString = ""; // Create the URL object and make a connection to it. url = new URL(targetURL); conn = url.openConnection(); // check out permission of acess URL if (conn.getPermission() != null) { returnString = "Do not Permission access URL "; } else { // Set connection parameters. We need to perform input and output, // so set both as true. conn.setDoInput(true); conn.setDoOutput(true); // Disable use of caches. conn.setUseCaches(false); // Set the content type we are POSTing. We impersonate it as // encoded form data conn.setRequestProperty("Content-Type", "application/x-www-form-urlencoded"); // get the output stream . out = new DataOutputStream(conn.getOutputStream()); String content = ""; // Create a single String value pairs for all the keys // in the Hashtable passed to us. Enumeration e = contentHash.keys(); boolean first = true; while (e.hasMoreElements()) { // For each key and value pair in the hashtable Object key = e.nextElement(); Object value = contentHash.get(key); // If this is not the first key-value pair in the hashtable, // concantenate an "&" sign to the constructed String if (!first) content += "&"; // append to a single string. Encode the value portion content += (String) key + "=" + URLEncoder.encode((String) value); first = false; } // Write out the bytes of the content string to the stream. out.writeBytes(content); out.flush(); out.close(); // check if can't read from URL // Read input from the input stream. in = new DataInputStream(conn.getInputStream()); String str; while (null != ((str = in.readLine()))) { returnString += str + "\n"; } in.close(); } // return the string that was read. return returnString; }

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  • Get a value from hashtable by a part of its key

    - by htf
    Hi. Say I have a Hashtable<String, Object> with such keys and values: apple => 1 orange => 2 mossberg => 3 I can use the standard get method to get 1 by "apple", but what I want is getting the same value (or a list of values) by a part of the key, for example "ppl". Of course it may yield several results, in this case I want to be able to process each key-value pair. So basically similar to the LIKE '%ppl%' SQL statement, but I don't want to use a (in-memory) database just because I don't want to add unnecessary complexity. What would you recommend?

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  • Tuning garbage collections for low latency

    - by elec
    I'm looking for arguments as to how best to size the young generation (with respect to the old generation) in an environment where low latency is critical. My own testing tends to show that latency is lowest when the young generation is fairly large (eg. -XX:NewRatio <3), however I cannot reconcile this with the intuition that the larger the young generation the more time it should take to garbage collect. The application runs on linux, jdk 6 before update 14, i.e G1 not available.

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  • How can I add a .jar to my build path in Eclipse?

    - by Roman
    I try to do it the following way: Right click on the name of the project. Click on Build Path in the drop dawn menu. Click on "Configure Build Path" And then I do not know what to do. Should I select "Source", "Projects", "Libraries", "Order and Export"? In "Libraries" I have "Add JARs..." and "Add External JARs...". What should I select? (I have already a .jar file in the lib folder of my project.) ADDED: If I click on "Add JARs" in the "Libraries" tab, I see the "lib" sub-folder but if I go there I do not see my .jar file there (and I know that it is there).

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  • Design pattern: polymorphisim for list of objects

    - by ziang
    Suppose I have a class A, and A1, A2 inherits from A. There are 2 functions: List<A1> getListA1(){...} List<A2> getListA2(){...} Now I want to do something similar to both A1 and A2 in another function public void process(List<A>){...} If I want to pass the instance of either ListA1 or ListA2, of course the types doesn't match because the compiler doesn't allow the coercion from List< A1 to List< A. I can't do something like this: List<A1> listA1 = getListA1(); List<A> newList = (List<A>)listA1; //this is not allowed. So what is the best approach to the process()? Is there any way to do it in a universal way rather than write the similar code to both List and List?

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  • How do I redirect to the current page in Servlet Filter?

    - by JeffJak
    I have a page say: /myapp/test.jsp?queryString=Y. The filter needs to redirect to current page. It should go to /myapp/test.jsp (without the query string). The below seems to bring it to to the context root: /myapp. I am running in WAS6.1. public void doFilter(ServletRequest req, ServletResponse resp, FilterChain chain) throws IOException, ServletException { HttpServletRequest httpReq = (HttpServletRequest) req; HttpServletResponse httpResp = (HttpServletResponse) resp; { boolean blnNeedToRedirect = true; if (blnNeedToRedirect) { httpResp.sendRedirect("."); return; } chain.doFilter(req, resp); }

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  • When to use @Singleton in a Jersey resource

    - by dexter
    I have a Jersey resource that access the database. Basically it opens a database connection in the initialization of the resource. Performs queries on the resource's methods. I have observed that when I do not use @Singleton, the database is being open at each request. And we know opening a connection is really expensive right? So my question is, should I specify that the resource be singleton or is it really better to keep it at per request especially when the resource is connecting to the database? My resource code looks like this: //Use @Singleton here or not? @Path(/myservice/) public class MyResource { private ResponseGenerator responser; private Log logger = LogFactory.getLog(MyResource.class); public MyResource() { responser = new ResponseGenerator(); } @GET @Path("/clients") public String getClients() { logger.info("GETTING LIST OF CLIENTS"); return responser.returnClients(); } ... // some more methods ... } And I connect to the database using a code similar to this: public class ResponseGenerator { private Connection conn; private PreparedStatement prepStmt; private ResultSet rs; public ResponseGenerator(){ Class.forName("org.h2.Driver"); conn = DriverManager.getConnection("jdbc:h2:testdb"); } public String returnClients(){ String result; try{ prepStmt = conn.prepareStatement("SELECT * FROM hosts"); rs = prepStmt.executeQuery(); ... //do some processing here ... } catch (SQLException se){ logger.warn("Some message"); } finally { rs.close(); prepStmt.close(); // should I also close the connection here (in every method) if I stick to per request // and add getting of connection at the start of every method // conn.close(); } return result } ... // some more methods ... } Some comments on best practices for the code will also be helpful.

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  • JSP: Use information from one page to another

    - by Sandeep Bansal
    Hi, I currently have a JSP page with a Form for the user to enter their name, but what I want is to get the user forwarded to a different JSP page after form submission and to carry on their name to be used. I don't want to use JSTL EL just simple JSP uses. I was thinking of using a bean storing the detail in a session but how would it work. Thanks.

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  • Find the gender from a name

    - by Ramesh
    Hi guys, I recently confronted with a weird yet interesting question. The questions is as follows: Need to write a program which can give the gender as output based on the name. Example: INPUT -- John Michael Britney OUTPUT-- male male female So this is the output I expect. I tried a lot to solve, but I really was not able to crack it. I will be really thankful to this site for giving me an opportunity to share this question. Actually this is asked in a programming contest as a flyer problem, so I thought this can be programmed.

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  • Trying to setup externalizing properties in spring

    - by Gandalf StormCrow
    Hi all, I'm building my project with maven so according to maven way, config should be in src/main/conf , how can I say to my spring application context that that is where jdbc.properties is found? Here is example bean : <bean id="propertyConfigurer" class="org.springframework.beans.factory.config.PropertyPlaceholderConfigurer"> <property name="location" value="jdbc.properties" /> </bean> Spring assumens that this configuration is inside src/main/webapp/WEB-INF, I hope I've been clear if not I'll rephrase my question thank you

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  • problem in extending a class

    - by Vineeth
    there are two classes public class Account { public Acconut() { //constructor } } public class SavingsAccount extends Account { } while doing the inheritance i have got an error message "cannont find symbol Symbol: constructor Account()" what might be the error in my code...??

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  • Refining Solr searches, getting exact matches?

    - by thebluefox
    Afternoon chaps, Right, I'm constructing a fairly complex (to me anyway) search system for a website using Solr, although this question is quite simple I think... I have two search criteria, location and type. I want to return results that are exact matches to type (letter to letter, no exceptions), and like location. My current search query is as follows ../select/?q=location:N1 type:blue&rows=100&fl=*,score&debugQuery=true This firstly returns all the type blue's that match N1, but then returns any type that matches N1, which is opposite to what I'm after. Both fields are set as textgen in the Solr schema. Any pointers? Cheers gang

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  • Please help me to allow my `JTable` to search the text even the table is in editable mode on key-press

    - by Ashish Pancholi
    If user starts pressing keys using keyboards then JTable is supposed to be searched the matching text for him and if user double clicks on cell then Table should allow him to edit the text. And the issue is - Table is only searching text when the table is in non-editable mode and if Table is editable and user starts typing the text-using keyboard, cell is allowing him to edit the cell rather then search. Mr mKorbel has just solved my issue to allow edit only if double click on Table cell. Please help me to allow my JTable to search the text even the table is in editable mode on key-press.

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