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• 0/1 Knapsack with irrational weights

  - by user356106

  Consider the 0/1 knapsack problem. The standard Dynamic Programming algorithm applies only when the capacity as well as the weights to fill the knapsack with are integers/ rational numbers. What do you do when the capacity/weights are irrational? The issue is that we can't memoize like we do for integer weights because we may need potentially infinite decimal places for irrational weights - leading to an infinitely large number of columns for the Dynamic Programming Table . Is there any standard method for solving this? Any comments on the complexity of this problem? Any heuristics? What about associated recurrences like (for example): f(x)=1, for x< sqrt(2) f(x)=f(x-sqrt(2))+sqrt(3)

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• rails db migration, undefined method `to_sym', cant figure out syntax

  - by oelbrenner

  the original migration looks like this: class CreateUsers true do |t| t.string :login, :limit = 40 t.string :name, :limit = 100, :default = '', :null = true t.string :email, :limit = 100 t.string :crypted_password, :limit = 40 t.string :salt, :limit = 40 t.string :remember_token, :limit = 40 t.datetime :remember_token_expires_at t.string :activation_code, :limit = 40 t.datetime :activated_at, :datetime t.string :state, :null = :no, :default = 'passive' t.datetime :deleted_at t.integer :occupation_id, :null = :yes t.datetime :paid_up_to_date, :date t.timestamps end and I am trying to change the default of "state" to be "active" instead of passive so my attempt at a migration looks like this: ( still learning.. be gentle ) class ChangeUserStateDefault < ActiveRecord::Migration def self.up change_column :users, :state, :null = :no, :default = 'active' end def self.down end end

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• designing database tables using JDBC

  - by Noona

  I am creating a users table using JDBC and mysql, each user has a permissions list that comprises Integer values, I am wondering if I should use an array for storing these values and then have only 1 record for this user in the table, or simply create a new table that comprises 2 columns: user ID and permissions, and then have multiple records for each user that specify the user name in one columns and one permission value in the second column, the second option seems to be redundant since a permission value is a simple object that isn't associated with any other objects (like a student and courses list for example, because the course is associated with many other objects, like grade, teacher, etc, so in this case it is natural to have multiple records), but the first one seems to be a bit unnatural to me, so if someone has experience with these things and direct me? thanks

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• Map null column as 0 in a legacy database (JPA)

  - by Indrek

  Using Play! framework and it's JPASupport class I have run into a problem with a legacy database. I have the following class: @Entity @Table(name="product_catalog") public class ProductCatalog extends JPASupport { @Id @GeneratedValue(strategy = GenerationType.IDENTITY) public Integer product_catalog; @OneToOne @JoinColumn(name="upper_catalog") public ProductCatalog upper_catalog; public String name; } Some product catalogs don't have an upper catalog, and this is referenced as 0 in a legacy database. If I supply the upper_catalog as NULL, then expectedly JPA inserts a NULL value to that database column. How could I force the null values to be 0 when writing to the database and the other way around when reading from the database?

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• Passing a enum value as a tag attribute in JSP

  - by Jakub

  I have a custom JSP tag which is using a parameter which is an enum. This approach is a consequence of using other classes which need this enumeration. The point is I have no clue how to assign an enum value in the EL: <mytaglib:mytag enumParam="${now what do I type here?}" /> The only workaround which I found so far was to make the enumParam an Integer and convert it to desired values: <mytaglib:mytag enumParam="3" /> I believe there must be a better way to do it. Please help.

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• A 4-byte Unsigned Int for Sql Server 2008?

  - by Jeff Meatball Yang

  I understand there are multiple questions about this on SO, but I have yet to find a definitive answer of "yes, here's how..." So here it is again: What are the possible ways to store an unsigned integer value (32-bit value or 32-bit bitmap) into a 4-byte field in SQL Server? Here are ideas I have seen: 1) Use a -1*2^31 offset for all values Disadvantages: need to perform math on the values before reading/writing/aggregating. 2) Use 4 tinyint fields Disadvantages: need to concatenate values to perform any operations 3) Use binary(4) Disadvantages: actually uses 4 + 2 bytes of space

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• Problems inserting file data into sqlite database using python

  - by tylerc230

  I'm trying to open an image file in python and add that data to an sqlite table. I created the table using: "CREATE TABLE "images" ("id" INTEGER PRIMARY KEY AUTOINCREMENT NOT NULL , "description" VARCHAR, "image" BLOB );" I am trying to add the image to the db using: imageFile = open(imageName, 'rb') b = sqlite3.Binary(imageFile.read()) targetCursor.execute("INSERT INTO images (image) values(?)", (b,)) targetCursor.execute("SELECT id from images") for id in targetCursor: imageid= id[0] targetCursor.execute("INSERT INTO %s (questionID,imageID) values(?,?)" % table, (questionId, imageid)) When I print the value of 'b' it looks like binary data but when I call: 'select image from images where id = 1' I get '????' printed to the console. Anyone know what I'm doing wrong?

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• VB.NET: I Cant find the index of an array

  - by steve

  This is the code for my array (which is working) Public numUsers As Integer Public fNameUsers As String = ("..\..\..\users.txt") Public UserRecords As Usersclass() 'note... this line is in a module ' reader = New System.IO.StreamReader(fNameUsers) numUsers = 0 'Split the array up at each delimiter of "," and add new objects ' Do While reader.Peek <> -1 ReDim Preserve UserRecords(numUsers) oneline = reader.ReadLine fields = oneline.Split(",") UserRecords(numUsers) = New Usersclass UserRecords(numUsers).AccountNumber = fields(0) UserRecords(numUsers).CourseName = fields(1) UserRecords(numUsers).FirstName = fields(2) UserRecords(numUsers).LastName = fields(3) UserRecords(numUsers).DOB = fields(4) UserRecords(numUsers).Email = fields(5) UserRecords(numUsers).CourseProgress = (6) UserRecords(numUsers).AdminCheck = fields(7) numUsers = numUsers + 1 Loop reader.Close() My problem is that I don't know how to lookup the index of an array where the .accountNumber = a variable. For example the acccountNumber is 253, what is the code to find the index this relates to???? Thanks in advance

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• Fibonacci Numbers in Haskell

  - by boraer

  Hi everbody I need to change my F# code to Haskell code but I am so new in Haskell and I can not this My code simply read data from keyboard if data not an integer return an error message then calculate the n fibonacci number then writes to a list after that writes the list into a txt file Here is my code open System let rec fib n = match n with |0->0 |1->1 |2->1 |n->fib(n-1)+fib(n-2);; let printFibonacci list = for i=0 to (List.length list)-1 do printf "%d " (list.Item(i));; let writeToFile list = let file = System.IO.File.Create("C:\out2.txt") let mutable s ="" let writer = new System.IO.StreamWriter(file) try for i=0 to (List.length list)-1 do s <- list.Item(i).ToString() writer.Write(s+" ") finally writer.Close() file.Dispose() printfn "Writed To File" let mutable control = true let mutable num = 0 while control do try printfn "Enter a Number:" num <- Convert.ToInt32(stdin.ReadLine()) let listFibonacci = [for i in 0 .. num-1->fib(i)] printFibonacci(listFibonacci) printfn "\n%A"(listFibonacci) writeToFile(listFibonacci) control<-false with | :? System.FormatException->printfn "Number Format Exception"; Console.ReadKey true|>ignore

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• problem with DataReader ASP.NET (Visual Basic)

  - by ZiGi

  Hey, I have this problem : [InvalidOperationException: No data exists for the row / column.] System.Data.OleDb.OleDbDataReader.DoValueCheck(Int32 ordinal) +1029063 System.Data.OleDb.OleDbDataReader.GetInt32(Int32 ordinal) +12 ASP.addsousvoyage_aspx.hdVoyage_SelectedIndexChanged(Object sender, EventArgs e) in C:\Users\ZiGi\Desktop\VisualDesign\addSousVoyage.aspx:222 System.Web.UI.WebControls.ListControl.OnSelectedIndexChanged(EventArgs e) +111 System.Web.UI.WebControls.DropDownList.RaisePostDataChangedEvent() +134 System.Web.UI.WebControls.DropDownList.System.Web.UI.IPostBackDataHandler.RaisePostDataChangedEvent() +10 System.Web.UI.Page.RaiseChangedEvents() +165 System.Web.UI.Page.ProcessRequestMain(Boolean includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint) +1485 When I do this : MsgBox(myReader1.GetInt32(0).ToString) Even if : MsgBox(myReader1.FieldCount) returning 1 as value and the field(0) is integer. What's the problem ?

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• write() in sys/uio.h returns -1

  - by fredrik

  I'm using Ubuntu Server 9.10 AMD Phenom 2 cpu g++ (Ubuntu 4.4.1-4ubuntu9) 4.4.1 trying to run the application pftp-shit v 1.11. The following code in tcp.cc is executed successfully: int outfile_fd = open(name, O_CREAT | O_TRUNC | O_RDWR | O_BINARY)) which returns a file descriptor int (in my case 6) - name is a char array containing a valid path to my file which successfully i created. and successfully running: fchmod(outfile_fd, S_IRUSR | S_IWUSR); and access(name, W_OK) The issue occurs during running the function (from sys/uio.h) write(outfile_fd, this-control_buffer, read_length) which returns -1. -1 is of returned if nothing was written and otherwise a non-negative integer is returned which is equal to the number of bytes written. Anyone having a clue how I can get the write function to work?

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• Send custom data when initializing java WebService over soap

  - by Mesni

  Hello. I have a question about sending additional data over soap to the functions. My webService function requests only one integer, for example an getDocumentPrivilage(DocumentID). In another WebService user registered and he got an unique ID, so the other application can see who he is. So on Service one he registers, gets id and it has to send it to the other webservice tor the privilage. Id dont wish to rewrite the function so that it gets the unique ID (like this getDocumentPrivilage(uniqID,DocumentID)) but, the wish is that i would be able to create a client that sends this data at the initialization or somehow as some sort of parameter behind the function. Is this possible?? I tried the ServiceLifecycle but cant see any setting i've given in. Im using WebSphere CE for the server and Jax-ws Creating the webapp in java. Thank you very much in advance. lp, Mesni

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• override the operator overloading in C++ ?

  - by stdnoit

  helo guys i have class call Complex I did operator overloading like such Complex c = a + b; // where a and b are object of Complex class which basically is operator+(Complex& that); but I dont know how to say for example double c = a + 10; //where a is object of Complex class but 10 is integer / double I did define typecasting for a to be double get my IDE says that there are too many operands + and it somehow complains for not being able to "understand" the + it has to be in this format though double c = a + 10; thanks

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• How do I use a Lambda expression to sort INTEGERS inside a object?

  - by punkouter

  I have a collection of objects and I know that I can sort by NAME (string type) by saying collEquipment.Sort((x, y) = string.Compare(x.ItemName, y.ItemName)); that WORKS. But I want to sort by a ID (integer type) and there is no such thing as Int32.Compare So how do I do this? This doesnt work collEquipment.Sort((x, y) = (x.ID < y.ID); //error I know the answer is going to be really simple. Lambda expressions confuse me.

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• whatz wrong in this SELECt query of MSSQL... ?

  - by user522211

  Protected Sub Page_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Load Dim SQLData As New System.Data.SqlClient.SqlConnection("Data Source=.\SQLEXPRESS;AttachDbFilename=|DataDirectory|\Database.mdf;Integrated Security=True;User Instance=True") Dim cmdSelect As New System.Data.SqlClient.SqlCommand("SELECT * FROM Table1 WHERE Date =" & TextBox1.Text & "'", SQLData) SQLData.Open() Dim dtrReader As System.Data.SqlClient.SqlDataReader = cmdSelect.ExecuteReader() While dtrReader.Read() For j As Integer = 1 To 31 Dim s As String = "s" & j If dtrReader(s.ToString()).ToString() = "b" Then Dim img As ImageButton = DirectCast(Panel1.FindControl(s.ToString()), ImageButton) img.ImageUrl = "~/Images/booked.gif" img.Enabled = False End If Next End While dtrReader.Close() SQLData.Close() End Sub SHOWS AN ERROR : Unclosed quotation mark after the character string ''.

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• technique for how to debug macros in C

  - by Dervin Thunk

  Hi. So I have the (mostly vilified) #define MAX( a, b ) ( ((a) > (b)) ? (a) : (b) ) somewhere in a program (yes, yes, I know). At some point in the code there is a comparison X>-1?, where X is (as far as I can tell) a (signed) integer. The line is j += MAX(bmGs[i], bmBc[(int)y[i + j]] - m + 1 + i);, where y here is a char*. Not necessarily surprisingly, I find that the macro is returning -1 as the larger number (I'm guessing too long a number for int or an unsigned issue, but I can't find it). I would like to know techniques you guys may have for finding these kinds of errors. Notice that I'm not asking for programming advice about whether or not to use that macro, I'm sure folks are dying to tell me I should refrain from things like that, but the question is going somewhere else. Thanks.

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• Why can I create a table with PRIMARY KEY on a nullable column?

  - by AlexKuznetsov

  The following code creates a table without raising any errors: CREATE TABLE test( ID INTEGER NULL, CONSTRAINT PK_test PRIMARY KEY(ID) ) Note that I cannot insert a NULL, as expected: INSERT INTO test VALUES(1),(NULL) ERROR: null value in column "id" violates not-null constraint DETAIL: Failing row contains (null). ********** Error ********** ERROR: null value in column "id" violates not-null constraint SQL state: 23502 Detail: Failing row contains (null). Why can I create a table with a self-contradictory definition? ID column is explicitly declared as NULLable, and it is implicitly not nullable, as a part of the PRIMARY KEY. Does it make sense? Edit: would it not be better if this self-contradictory CREATE TABLE just failed right there?

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• Space requirements of a merge-sort

  - by Arkaitz Jimenez

  I'm trying to understand the space requirements for a Mergesort, O(n). I see that time requirements are basically, amount of levels(logn) * merge(n) so that makes (n log n). Now, we are still allocating n per level, in 2 different arrays, left and right. I do understand that the key here is that when the recursive functions return the space gets deallocated, but I'm not seeing it too obvious. Besides, all the info I find, just states space required is O(n) but don't explain it. Any hint? function merge_sort(m) if length(m) = 1 return m var list left, right, result var integer middle = length(m) / 2 for each x in m up to middle add x to left for each x in m after middle add x to right left = merge_sort(left) right = merge_sort(right) result = merge(left, right) return result

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• Dynamic upsert in postgresql

  - by Daniel

  I have this upsert function that allows me to modify the fill_rate column of a row. CREATE FUNCTION upsert_fillrate_alarming(integer, boolean) RETURNS VOID AS ' DECLARE num ALIAS FOR $1; dat ALIAS FOR $2; BEGIN LOOP -- First try to update. UPDATE alarming SET fill_rate = dat WHERE equipid = num; IF FOUND THEN RETURN; END IF; -- Since its not there we try to insert the key -- Notice if we had a concurent key insertion we would error BEGIN INSERT INTO alarming (equipid, fill_rate) VALUES (num, dat); RETURN; EXCEPTION WHEN unique_violation THEN -- Loop and try the update again END; END LOOP; END; ' LANGUAGE 'plpgsql'; Is it possible to modify this function to take a column argument as well? Extra bonus points if there is a way to modify the function to take a column and a table.

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• How do you find the last element of an array while iterating using a foreach loop in php ?

  - by Vaibhav Kamble

  I am writing a sql query creator using some parameters. While doing that ,I came across this problem. In java , Its very easy to detect the last element of an array from inside the for loop by just checking the current array position with the array length. for(int i=0; i< arr.length;i++){ boolean isLastElem = i== (arr.length -1) ? true : false; } php has some different fashion. They have non integer indexes to access arrays. So you must iterate over an array using foreach loop. But it becomes very problematic when you need to take some decision (in my case to append or/and parameter while building query). I am sure there must be some standard way of doing this. How do you solve this problem normally in php ?

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• Wrong intrepretation of some columns in ireport

  - by Purushotham

  Hi, I got a strange problem. I am using iReport 3.7.1 tool to create some reports. The Query Editor has one query. It shows all the data types of the fields in that query exactly same as the data types shown when I execute it using SQLYOG editor. The problem is here: One field data type is mismatched. I don't know the reason. SQLYOG says it is INTEGER whereas iReport Query Editor says its a long value. BTW The value that assigned to that filed is zero. Can anyone help ? I want to zero-in on this issue.

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• manage date fields when are int in the db

  - by Luca Romagnoli

  Hi in my db there is a field "date_start" type integer. This is the part of form for this field <div class="editor-label"> <%: Html.LabelFor(model => model.date_start) %> </div> <div class="editor-field"> <%: Html.TextBoxFor(model => model.date_start, new { @class = "calendar" })%> <%: Html.ValidationMessageFor(model => model.date_start) %> </div> In the form i want that the field's format is date type. and memorize it in int type after calling a my function for the convertion. How can i manage it? thanks

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• Store the day of the week and time

  - by bsiddiqui

  I have a two part question about storing day(s) of the week and time in a database. I'm using Rails 4.0, ruby 2.0.0, and postgres. I have certain events and those events have a schedule. For the event Skydiving for example, for example, I might have Tuesday and Wednesday and 3 pm. 1) Is there a way for me to store the the record for Tuesday and Wednesday in one row or do should I have two records? 2) What is the best way to store the day and time? Is there a way to store day of week and time (not datetime) or should these be separate columns? If they should be separate, how would you store day of week? I was thinking of storing them as integer values (0 for Sunday, 1 for Monday, etc) since that's how wday method for the Time class does it. Any suggestions would be super helpful. Thanks!

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• how to print number with commas as thousands separators in Javascript

  - by mikez302

  I am trying to print an integer in Javascript with commas as thousands separators. For example, I want to show the number 1234567 as "1,234,567". How would I go about doing this? Here is how I am doing it: function numberWithCommas(x) { x = x.toString(); var pattern = /(-?\d+)(\d{3})/; while (pattern.test(x)) x = x.replace(pattern, "$1,$2"); return x; } I am wondering if anyone has a simpler or more elegant idea. It would be nice if it works with floats also, but that is not necessary. It does not need to be locale-specific to decide between periods and commas.

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• Getting ListView values into a string array?

  - by Andrew

  I have a ListView control set up in details mode, and on a button press I would like to retrieve all column values from that row in the ListView. This is my code so far: Private Sub Button3_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button3.Click Dim items As ListView.SelectedListViewItemCollection = _ Me.ManageList.SelectedItems Dim item As ListViewItem Dim values(0 To 4) As String Dim i As Integer = 0 For Each item In items values(i) = item.SubItems(1).Text i = i + 1 Next End Sub But values just comes out as an empty array. Any ideas? I just want the values array to be filled with the data of that ListView row. Cheers.

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