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• Sum of path products in DAG

  - by Jules

  Suppose we have a DAG with edges labeled with numbers. Define the value of a path as the product of the labels. For each (source,sink)-pair I want to find the sum of the values of all the paths from source to sink. You can do this in polynomial time with dynamic programming, but there are still some choices that can be made in how you decompose the problem. In my case I have one DAG that has to be evaluated repeatedly with different labelings. My question is: for a given DAG, how can we pre-compute a good strategy for computing these values for different labelings repeatedly. It would be nice if there was an algorithm that finds an optimal way, for example a way that minimizes the number of multiplications. But perhaps this is too much to ask, I would be very happy with an algorithm that just gives a good decomposition.

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• Regular Expressions, Checking for a range of occurrences

  - by gmcalab

  I have a phone number I want to match against a regular expression. The format of the phone number must match this: (123) 123-4567 x12345 The extension is optional. Also the extension must contain 1-5 numbers. Below is a regular expression I wrote that works. ^\(\d{3}\) \d{3}-\d{4}( x\d\d?\d?\d?\d?)?$ I was wondering if there is a better way to check for the extension instead of x\d\d?\d?\d?\d? Can I say 1-5 occurrences of \d instead of the above some how ?

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• Problems with Linked List in C

  - by seePhor

  Hey everyone, I am new to C and I am working on an XOR linked list for a project. I have most of the code done, but I can't seem to get the delete function of the list to work properly. It seems able to delete some numbers, but not any number you pass into the function. Could anyone experienced with C take a look and possibly point out where I went wrong? I have been working on this for a while now and have not had much luck and I have started over 3 times :( Any help is much appreciated. Thank you. You can see my first attempt of code here. I can only post one link, so if you would like to see my second attempt, just tell me so and I can email it to you or something. Thank you for your time.

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• How is schoolbook long division an O(n^2) algorithm?

  - by eSKay

  Premise: This Wikipedia page suggests that the computational complexity of Schoolbook long division is O(n^2). Deduction: Instead of taking "Two n-digit numbers", if I take one n-digit number and one m-digit number, then the complexity would be O(n*m). Contradiction: Suppose you divide 100000000 (n digits) by 1000 (m digits), you get 100000, which takes six steps to arrive at. Now, if you divide 100000000 (n digits) by 10000 (m digits), you get 10000 . Now this takes only five steps. Conclusion: So, it seems that the order of computation should be something like O(n/m). Question: Who is wrong, me or Wikipedia, and where?

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• Java: confirm method Binary division and find remainder is correct?

  - by cadwag

  I am parsing binary files and have to implement a CRC algorithm to ensure the file is not corrupted. Problem is that I can't seem to get the binary math working when using larger numbers. The example I'm trying to get working: BigInteger G = new BigInteger("11001", 2); BigInteger M = new BigInteger("1110010000", 2); BigInteger R = M.remainder(G); I am expecting: R = "0101" But I am getting: R = "1100" I am assuming the remainder of 0101 is correct since it is given to me in this book I am using as a reference for the CRC algorithm (it's not based in Java), but I can't seem to get it working. I can get small binary calculations to work that I have solved by hand, but not the larger ones. I'll admit that I haven't worked the larger ones by hand yet, that is my next step, but I wanted to see if someone could point out a glaring flaw I have in my code. Can anyone confirm or deny that my methodology is correct? Thanks

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• OpenID and Authlogic - login and password?

  - by skrat

  How can I get rid of validation messages telling me that: Login is too short (minimum is 3 characters) Login should use only letters, numbers, spaces, and .-_@ please. Password is too short (minimum is 4 characters) Password confirmation is too short (minimum is 4 characters) this happens even before map_openid_registration is called, thus not giving me any chance to fill login with something from returned registration Hash. I would like to have OpenID auto-registration (on login) without requiring user to supply login/password. I also won't make this fields "not required" or "not validated", since I still need them with old school login/password registration. Thank you

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• Equivalent of LaTeX's \label and \ref in HTML.

  - by dreeves

  I have an FAQ in HTML (example) in which the questions refer to each other a lot. That means whenever we insert/delete/rearrange the questions, the numbering changes. LaTeX solves this very elegantly with \label and \ref -- you give items simple tags and LaTeX worries about converting to numbers in the final document. How do people deal with that in HTML? ADDED: Note that this is no problem if you don't have to actually refer to items by number, in which case you can set a tag with <a name="foo"> and then link to it with <a href="#foo">some non-numerical way to refer to foo</a>. But I'm assuming "foo" has some auto-generated number, say from an <ol> list, and I want to use that number to refer to and link to it.

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• Using 'load' in octave

  - by lollygagger

  Is there a way to tell the load function to only load until a certain line? I want to read in a data file and assign the numbers to an array, however, I want it to stop after it has created a 200 X 200. Could I also do this with a do-while loop and fgetl? When I try to use fgetl(fid, len) and give it 'len', it does not obey :-/ How can I tell octave to ignore the comment lines in an input file? They are '#' characters, so I figured octave would just automatically ignore them, but not so... Thanks.

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• Confusion Matrix with number of classified/misclassified instances on it (Python/Matplotlib)

  - by Pinkie

  I am plotting a confusion matrix with matplotlib with the following code: from numpy import * import matplotlib.pyplot as plt from pylab import * conf_arr = [[33,2,0,0,0,0,0,0,0,1,3], [3,31,0,0,0,0,0,0,0,0,0], [0,4,41,0,0,0,0,0,0,0,1], [0,1,0,30,0,6,0,0,0,0,1], [0,0,0,0,38,10,0,0,0,0,0], [0,0,0,3,1,39,0,0,0,0,4], [0,2,2,0,4,1,31,0,0,0,2], [0,1,0,0,0,0,0,36,0,2,0], [0,0,0,0,0,0,1,5,37,5,1], [3,0,0,0,0,0,0,0,0,39,0], [0,0,0,0,0,0,0,0,0,0,38] ] norm_conf = [] for i in conf_arr: a = 0 tmp_arr = [] a = sum(i,0) for j in i: tmp_arr.append(float(j)/float(a)) norm_conf.append(tmp_arr) plt.clf() fig = plt.figure() ax = fig.add_subplot(111) res = ax.imshow(array(norm_conf), cmap=cm.jet, interpolation='nearest') cb = fig.colorbar(res) savefig("confmat.png", format="png") But I want to the confusion matrix to show the numbers on it like this graphic (the right one): http://i48.tinypic.com/2e30kup.jpg How can I plot the conf_arr on the graphic?

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• SQLServer 2008 Pivot

  - by Mitch

  I need to show some information in a graph, the data is held in a SQL Server 2008 table. The graph is expecting 2 columns, one for QuestionNumber and the other for Score. The table containing the data has column names that correspond to the question numbers ie A1, A2, A3, A4, B1, B2, B3, B4, C1, C2. Each question is given a score of 1 to 5. I need to show a graph where the X axis shows A1, A2, A3 etc and the Y axis shows the score. I'm thinking I somehow need to rotate the data to achive this, but I'm not sure how. Maybe a different technique can acheive this rather that a Rotate, so I'm open to any ideas.

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• How to have localized style when writing cell with xlwt

  - by lfagundes

  I'm writing an Excel spreadsheet with Python's xlwt and I need numbers to be formatted using "." as thousands separator, as it is in brazilian portuguese language. I have tried: style.num_format_str = r'#,##0' And it sets the thousands separator as ','. If I try setting num_format_str to '#.##0', I'll get number formatted as 1234.000 instead of 1.234. And if I open document in OpenOffice and format cells, I can set the language of the cell to "Portuguese (Brazil)" and then OpenOffice will show the format code as being "#.##0", but I don't find a way to set the cell's language to brazilian portuguese. Any ideas?

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• Dispelling the UIImage imageNamed: FUD

  - by Roger Nolan

  I see a lot of people saying imageNamed is bad but equal numbers of people saying the performance is good - especially when rendering UITableViews. See this SO question for example or this article on iPhoneDeveloperTips.com UIImage's imageNamed method used to leak so it was best avoided but has been fixed in recent releases. I'd like to understand the caching algorithm better in order to make a reasoned decision about where I can trust the system to cache my images and where I need to go the extra mile and do it myself. My current basic understanding is that it's a simple NSMutableDictionary of UIImages referenced by filename. It gets bigger and when memory runs out it gets a lot smaller. For example, does anyone know for sure that the image cache behind imageNamed does not respond to didReceiveMemoryWarning? It seems unlikely that Apple would not do this. If you have any insight into the caching algorithm, please post it here.

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• Reading numeric Excel data as text using xlrd in Python

  - by Brian

  Hi guys, I am trying to read in an Excel file using xlrd, and I am wondering if there is a way to ignore the cell formatting used in Excel file, and just import all data as text? Here is the code I am using for far: import xlrd xls_file = 'xltest.xls' xls_workbook = xlrd.open_workbook(xls_file) xls_sheet = xls_workbook.sheet_by_index(0) raw_data = [['']*xls_sheet.ncols for _ in range(xls_sheet.nrows)] raw_str = '' feild_delim = ',' text_delim = '"' for rnum in range(xls_sheet.nrows): for cnum in range(xls_sheet.ncols): raw_data[rnum][cnum] = str(xls_sheet.cell(rnum,cnum).value) for rnum in range(len(raw_data)): for cnum in range(len(raw_data[rnum])): if (cnum == len(raw_data[rnum]) - 1): feild_delim = '\n' else: feild_delim = ',' raw_str += text_delim + raw_data[rnum][cnum] + text_delim + feild_delim final_csv = open('FINAL.csv', 'w') final_csv.write(raw_str) final_csv.close() This code is functional, but there are certain fields, such as a zip code, that are imported as numbers, so they have the decimal zero suffix. For example, is there is a zip code of '79854' in the Excel file, it will be imported as '79854.0'. I have tried finding a solution in this xlrd spec, but was unsuccessful.

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• T-SQL Re-Assigning Order Numbering

  - by Meltdown

  Say I have a table with a field called "ordernum" that denotes the order of a given set of rows. Now imagine that I delete one of these rows. What type of query would work best for re-assigning the order numbers so that they remain sequential? Here's an example: id group_id name ordernum active --------------------------------------------------- 0_____0______'Name1'___5__true 1_____0______'Name2'___4__true 2_____0______'Name3'___3__true 3_____1______'Name4'___2__true 4_____1______'Name5'__1__true 5_____1______'Name6'__NULL___false Now if I deleted the column with id='4' how would I reset the values in the 'ordernum' field for that specific group? Is this even possible? Or if I added a new row. (The first time the rows are created they are sorted by date, but then the user has the option to set the order himself.) In my table design I have a column 'active' boolean. If 'active' is set to false, then 'ordernum' is set to NULL. Otherwise it should be given an order number.

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• Unique identifiers for users

  - by Christopher McCann

  If I have a table of a hundred users normally I would just set up an auto-increment userID column as the primary key. But if suddenly we have a million users or 5 million users then that becomes really difficult because I would want to start becoming more distributed in which case an auto-increment primary key would be useless as each node would be creating the same primary keys. Is the solution to this to use natural primary keys? I am having a real hard time thinking of a natural primary key for this bunch of users. The problem is they are all young people so they do not have national insurance numbers or any other unique identifier I can think of. I could create a multi-column primary key but there is still a chance, however miniscule of duplicates occurring. Does anyone know of a solution? Thanks

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• C - floating point rounding

  - by hatorade

  I'm trying to understand how floating point numbers work. I think I'd like to test out what I know / need to learn by evaluating the following: I would like to find the smallest x such that x + 1 = x, where x is a floating point number. As I understand it, this would happen in the case where x is large enough so that x + 1 is closer to x than the next number higher than x representable by floating point. So intuitively it seems it would be the case where I don't have enough digits in the significand. Would this number x then be the number where the significand is all 1's. But then I can't seem to figure out what the exponent would have to be. Obviously it would have to be big (relative to 10^0, anyway).

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• search & replace on 3000 row, 25 column spreadsheet

  - by Deca

  I'm attempting to clean up data in this (old) spreadsheet and need to remove things like single and double quotes, HTML tags and so on. Trouble is, it's a 3000 row file with 25 columns and every spreadsheet app I've tried (NeoOffice, MS Excel, Apple Numbers) chokes on it. Hard. Any ideas on how else I can clean this thing up for import to MySQL? Clearly I could go through each record manually, row by row, but would like to avoid that if at all possible. Likewise, I could write a PHP script to handle it on import, but don't want to put the server into a death spiral either.

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• Memory footprint of a parsed XML file in Classic ASP?

  - by Pete Duncanson

  Anyone know of a way to find out the amount of memory/size of a XMLDocument once it has parsed a XML file? I've been doing "beer mat" calculations so far but have been asked to come up with some more legit numbers through monitoring some how. I need to create about 1500 XML files (via FreeThreadedXMl-DOM object), which verge between 3-9K in size and store them in Application vars but our SysAdmin is worried about us gobbling up too much memory. Other than the crude method of booting up a fresh IIS instance and then loading everything in and monitoring before and after memory usage in Task Manager I can't think of a way of doing it with a bit more accuracy.

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• math syntax checker written in python

  - by neurino

  All I need is to check, using python, if a string is a valid math expression or not. For simplicity let's say I just need + - * / operators (+ - as unary too) with numbers and nested parenthesis. I add also simple variable names for completeness. So I can test this way: test("-3 * (2 + 1)") #valid test("-3 * ") #NOT valid test("v1 + v2") #valid test("v2 - 2v") #NOT valid ("2v" not a valid variable name) I tried pyparsing but just trying the example: "simple algebraic expression parser, that performs +,-,*,/ and ^ arithmetic operations" I get passed invalid code and also trying to fix it I always get wrong syntaxes being parsed without raising Exceptions just try: >>>test('9', 9) 9 qwerty = 9.0 ['9'] => ['9'] >>>test('9 qwerty', 9) 9 qwerty = 9.0 ['9'] => ['9'] both test pass... o_O Any advice?

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• How to code Fizzbuzz in F#

  - by Russell

  I am currently learning F# and have tried (an extremely) simple example of FizzBuzz. This is my initial attempt: for x in 1..100 do if x % 3 = 0 && x % 5 = 0 then printfn "FizzBuzz" elif x % 3 = 0 then printfn "Fizz" elif x % 5 = 0 then printfn "Buzz" else printfn "%d" x What solutions could be more elegant/simple/better (explaining why) using F# to solve this problem? Note: The FizzBuzz problem is going through the numbers 1 to 100 and every multiple of 3 prints Fizz, every multiple of 5 prints Buzz, every multiple of both 3 AND 5 prints FizzBuzz. Otherwise, simple the number is displayed. Thanks :)

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• Do I need to use decimal places when using floats? Is the "f" suffix necessary?

  - by Paulo Fierro

  I've seen several examples in books and around the web where they sometimes use decimal places when declaring float values even if they are whole numbers, and sometimes using an "f" suffix. Is this necessary? For example: [UIColor colorWithRed:0.8 green:0.914 blue:0.9 alpha:1.00]; How is this different from: [UIColor colorWithRed:0.8f green:0.914f blue:0.9f alpha:1.00f]; Does the trailing "f" mean anything special? Getting rid of the trailing zeros for the alpha value works too, so it becomes: [UIColor colorWithRed:0.8 green:0.914 blue:0.9 alpha:1]; So are the decimal zeros just there to remind myself and others that the value is a float? Just one of those things that has puzzled me so any clarification is welcome :)

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• Validate a string in a table in SQL Server

  - by Ashish Gupta

  I need to check If a column value (string) in SQL server table starts with a small letter and can only contain '_', '-', numbers and alphabets. I know I can use a SQL server CLR function for that. However, I am trying to implement that validation using a scalar UDF and could make very little here...I can use 'NOT LIKE', but I am not sure how to make sure I validate the string irrespective of the order of characters or in other words write a pattern in SQL for this. Am I better off using a SQL CLR function? Any help will be appreciated.. Thanks in advance

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• Sorting array containing strings in objective c

  - by jakob

  Hello experts! I have an array named 'names' with strings looking like this: ["name_23_something", "name_25_something", "name_2_something"]; Now I would like to sort this array in ascending order so it looks like this: ["name_25_something", "name_23_something", "name_2_something"]; I guess that should start of with extracting the numbers since I want that the sorting is done by them: for(NSString *name in arr) { NSArray *nameSegments = [name componentsSeparatedByString:@"_"]; NSLog("number: %@", (NSString*)[nameSegments objectAtIndex:1]); } I'm thinking of creating a dictionary with the keys but I'm not sure if that is the correct objective-c way, maybe there some some methods I could use instead? Could you please me with some tips or example code how this sorting should be done in a proper way. Thank you

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• Compatibility issues with <a> and calling a function(); across different web browsers

  - by Matthew

  Hi, I am new to javascript. I wrote the following function rollDice() to produce 5 random numbers and display them. I use an anchor with click event to call the function. Problem is, in Chrome it won't display, works fine in IE, in firefox the 5 values display and then the original page w/anchor appears! I am suspicious that my script tag is too general but I am really lost. Also if there is a display function that doesn't clear the screen first that would be great. diceArray = new Array(5) function rollDice() { var i; for(i=0; i<5; i++) { diceArray[i]=Math.round(Math.random() * 6) % 6 + 1; document.write(diceArray[i]); } } when I click should display 5 rand variables

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• Compact a given array problem

  - by Bragaadeesh

  Dont know whether this is a duplicate, but this was an interview question asked to me. Given an array of random numbers and -1 placed inbetween, I have to compact the array meaning all the -1s are to be replaced and the final output should be the last valid index with the fresh array. For example. Input: 3 4 -1 -1 -1 5 8 -1 8 Output: 3 4 5 8 8 5 8 -1 8 and last valid index is 4 Input: -1 -1 -1 -1 -1 2 Output: 2 -1 -1 -1 -1 2 and last valid index is 0 Input: -1 -1 -1 3 3 3 Output: 3 3 3 3 3 3 and last valid index is 2 You should not swap the values just the last valid index along with the array is enough to decipher the non negative values.

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