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• Subversion update misses new directories

  - by Mike Q

  Hi all, Periodically we have trouble with SVN when doing updates. Very occasionally when someone adds a new directory doing an update through Tortoise doesn't work. If we do a "Fully Recursive" update using "Update from revision..." option then it picks it up fine. I'm poked around and seen this question which is virtually identical but with no answer. I've found the item on the SVN website, referenced by that post, that talks about an issue in 1.6.0 which is now fixed. However my SVN version is 1.6.9 and Tortoise is 1.6.7 so I wouldn't expect to have this problem any more. This only seems to occur with new directories, never seen it for individual files. We may have had older versions of Tortoise at one point (can't remember which tho) so maybe some issue has been introduced into our repo that an upgrade doesn't solve. We have the workaround but it wastes a few minutes of head-scratching after failed builds to figure it out and people who haven't come across this problem before really struggle until they ask someone else. Anyone know if this is a known bug and any permanent solutions? Thanks.

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• breadth-first traversal of directory tree is not lazy

  - by user855443

  I try to traverse the diretory tree. A naive depth-first traversal seems not to produce the data in a lazy fashion and runs out of memory. I next tried a breadth first approach, which shows the same problem - it uses all the memory available and then crashes. the code i have is: getFilePathBreadtFirst :: FilePath -> IO [FilePath] getFilePathBreadtFirst fp = do fileinfo <- getInfo fp res :: [FilePath] <- if isReadableDirectory fileinfo then do children <- getChildren fp lower <- mapM getFilePathBreadtFirst children return (children ++ concat lower) return (children ++ concat () else return [fp] -- should only return the files? return res getChildren :: FilePath -> IO [FilePath] getChildren path = do names <- getUsefulContents path let namesfull = map (path </>) names return namesfull testBF fn = do -- crashes for /home/frank, does not go to swap fps <- getFilePathBreadtFirst fn putStrLn $ unlines fps I think all the code is either linear or tail recursive, and I would expect that the listing of filenames starts immediately, but in fact it does not. Where is the error in my code and my thinking? where have I lost lazy evaluation?

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• Pascals Triangle by recursion

  - by Olpers

  Note : My Class Teacher gave me this question as an assignment... I am not asked to do it but please tell me how to do it with recursion Binomial coefficients can be calculated using Pascal's triangle: 1 n = 0 1 1 1 2 1 1 3 3 1 1 4 6 4 1 n = 4 Each new level of the triangle has 1's on the ends; the interior numbers are the sums of the two numbers above them. Task: Write a program that includes a recursive function to produce a list of binomial coefficients for the power n using the Pascal's triangle technique. For example, Input = 2 Output = 1 2 1 Input = 4 Output = 1 4 6 4 1 done this So Far but tell me how to do this with recursion... #include<stdio.h> int main() { int length,i,j,k; //Accepting length from user printf("Enter the length of pascal's triangle : "); scanf("%d",&length); //Printing the pascal's triangle for(i=1;i<=length;i++) { for(j=1;j<=length-i;j++) printf(" "); for(k=1;k<i;k++) printf("%d",k); for(k=i;k>=1;k--) printf("%d",k); printf("\n"); } return 0; }

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• Tree iterator, can you optimize this any further?

  - by Ron

  As a follow up to my original question about a small piece of this code I decided to ask a follow up to see if you can do better then what we came up with so far. The code below iterates over a binary tree (left/right = child/next ). I do believe there is room for one less conditional in here (the down boolean). The fastest answer wins! The cnt statement can be multiple statements so lets make sure this appears only once The child() and next() member functions are about 30x as slow as the hasChild() and hasNext() operations. Keep it iterative <-- dropped this requirement as the recursive solution presented was faster. This is C++ code visit order of the nodes must stay as they are in the example below. ( hit parents first then the children then the 'next' nodes). BaseNodePtr is a boost::shared_ptr as thus assignments are slow, avoid any temporary BaseNodePtr variables. Currently this code takes 5897ms to visit 62200000 nodes in a test tree, calling this function 200,000 times. void processTree (BaseNodePtr current, unsigned int & cnt ) { bool down = true; while ( true ) { if ( down ) { while (true) { cnt++; // this can/will be multiple statesments if (!current->hasChild()) break; current = current->child(); } } if ( current->hasNext() ) { down = true; current = current->next(); } else { down = false; current = current->parent(); if (!current) return; // done. } } }

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• PHP: Formatting multi-dimensional array as HTML?

  - by Industrial

  Hi everybody, I have tried to get my head around building a recursive function to handle formatting of a unknown depth multi-dimensional array to HTML and nested Divs. I thought that it should be a piece of cake, but no. Here's what I have come up with this far: function formatHtml($array) { $var = '<div>'; foreach ($array as $k => $v) { if (is_array($v['children']) && !empty($v['children'])) { formatHtml($v['children']); } else { $var .= $v['cid']; } } $var.= '</div>'; return $var; } And here's my array: Array ( [1] => Array ( [cid] => 1 [_parent] => [id] => 1 [name] => 'Root category' [children] => Array ( [2] => Array ( [cid] => 2 [_parent] => 1 [id] => 3 [name] => 'Child category' [children] => Array () ) ) ) ) Thanks a lot!

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• Strange thread behavior in Perl

  - by Zaid

  Tom Christiansen's example code (à la perlthrtut) is a recursive, threaded implementation of finding and printing all prime numbers between 3 and 1000. Below is a mildly adapted version of the script #!/usr/bin/perl # adapted from prime-pthread, courtesy of Tom Christiansen use strict; use warnings; use threads; use Thread::Queue; sub check_prime { my ($upstream,$cur_prime) = @_; my $child; my $downstream = Thread::Queue->new; while (my $num = $upstream->dequeue) { next unless ($num % $cur_prime); if ($child) { $downstream->enqueue($num); } else { $child = threads->create(\&check_prime, $downstream, $num); if ($child) { print "This is thread ",$child->tid,". Found prime: $num\n"; } else { warn "Sorry. Ran out of threads.\n"; last; } } } if ($child) { $downstream->enqueue(undef); $child->join; } } my $stream = Thread::Queue->new(3..shift,undef); check_prime($stream,2); When run on my machine (under ActiveState & Win32), the code was capable of spawning only 118 threads (last prime number found: 653) before terminating with a 'Sorry. Ran out of threads' warning. In trying to figure out why I was limited to the number of threads I could create, I replaced the use threads; line with use threads (stack_size => 1);. The resultant code happily dealt with churning out 2000+ threads. Can anyone explain this behavior?

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• Sorting by some field and fetching whole tree from DB

  - by Niaxon

  Hello everyone, I am trying to do file browser in a tree form and have a problem to sort it somehow. I use PHP and MySQL for that. I've created mixed (nested set + adjacency) table 'element' with the following fields: element_id, left_key, right_key, level, parent_id, element_name, element_type (enum: 'folder','file'), element_size. Let's not discuss right now that it is better to move information about element (name, type, size) into other table. Function to scan specified directory and fill table work correctly. Noteworthy, i am adding elements to tree in specific order: folders first and only files. After that i can easily fetch and display whole table on the page using simple query: SELECT * FROM element WHERE 1=1 ORDER BY left_key With the result of that query and another function i can generate correct html code (<ul><li>... and so on). Now back to the question (finally, huh?). I am struggling to add sorting functionality. For example i want to order my result by size. Here i need to keep in my mind whole hierarchy of tree and rule: folders first, files later. I believe i can do that by generating in PHP recursive query: SELECT * FROM element WHERE parent_id = {$parentId} ORDER BY element_type (so folders would be first), size (or name for example) After that for each result which is folder i will send another query to get it's content. Also it's possible to fetch whole tree by left_key and after that sort it in PHP as array but i guess that would be worse :) I wonder if there is better and more efficient way to do such thing?

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• Has anyone ever had OpenCV work with Python 2.7 on MacOS 10.6?

  - by ?????

  I've been trying on and off for the past 6 months to get OpenCV to work with Python on MacOS. Every time there's a new release, I try again and fail. I've tried both 64-bit and 32-bit, and both the xcode gcc and gcc installed via macports. I just spend the past two days on it, hopeful that the latest OpenCV release, that appears to include Python support directly would work. It doesn't. I've also tried and failed to use this: http://code.google.com/p/pyopencv/ I've been using OpenCV with C++ or Microsoft C++/CLI for the past few years, but I'd love to use it with Python on a Mac because that is my primary development environment. I'd love to hear from anyone who's actually been able to get the opencv python examples to run under Mac OS 10.6, either 32 or 64-bit. My last attempt was to follow the instructions on this page http://recursive-design.com/blog/2010/12/14/face-detection-with-osx-and-python/ with a clean, fresh install of 10.6 on a 64-bit capable Mac. My PYTHONPATH is set, and I can see the cv library in it. But an "import cv" from python fails. Previously, the closest I've ever gotten (again, staring on a clean, fresh 10.6 install) was this: Python 2.7.1 (r271:86882M, Nov 30 2010, 10:35:34) [GCC 4.2.1 (Apple Inc. build 5664)] on darwin Type "help", "copyright", "credits" or "license" for more information. >>> import cv Fatal Python error: Interpreter not initialized (version mismatch?) Abort trap thrilllap-2:~ swirsky$ I've seen a lot of folks answering similar questions here, but have never seen an definitive answer for it.

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• PHP: Three item validation comparison

  - by DavidYell

  I have 3 featured product panels on the homepage, and I'm writing a CMS page for it. I'm trying to validate the items. They are selected via three <select> elements, featured1, featured2 and featured3. The default is <option value="0" selected>Select an element</option> I need to validate the $_POST to ensure that the user hasn't selected the same product for more than one of the panels. I have worked out that each $_POST needs to be $_POST['featuredN'] > 0 but I can't seem to find a logical way of processing the 7 potential outcomes. Using a logic table, where 1 is a set value. 1 2 3 ------- 0 0 0 1 1 1 1 0 0 0 1 0 0 0 1 1 1 0 0 1 1 If an item is 0, then I will not update it, but I want the user to be able to update a single item if needs be. I cannot find a logical way to see if the item is not 0, and then compare it to another item if that also is not 0. So far my colleague suggested, adding up the values. Which works to see if condition 1 0 0 0 is not met. I have a vague feeling that some form of recursive function might be in order, but I can't quite get my brain to help me on this one! So to the collective brain! :)

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• Fortran severe (40) Error... Help?!

  - by Taka

  I can compile but when I run I get this error "forrtl: severe (40): recursive I/O operation, unit -1, file unknown" if I set n = 29 or more... Can anyone help with where I might have gone wrong? Thanks. PROGRAM SOLUTION IMPLICIT NONE ! Variable Declaration INTEGER :: i REAL :: dt DOUBLE PRECISION :: st(0:9) DOUBLE PRECISION :: stmean(0:9) DOUBLE PRECISION :: first_argument DOUBLE PRECISION :: second_argument DOUBLE PRECISION :: lci, uci, mean REAL :: exp1, n REAL :: r, segma ! Get inputs WRITE(*,*) 'Please enter number of trials: ' READ(*,*) n WRITE(*,*) dt=1.0 segma=0.2 r=0.1 ! For n Trials st(0)=35.0 stmean(0)=35.0 mean = stmean(0) PRINT *, 'For ', n ,' Trials' PRINT *,' 1 ',st(0) ! Calculate results DO i=0, n-2 first_argument = r-(1/2*(segma*segma))*dt exp1 = -(1/2)*(i*i) second_argument = segma*sqrt(dt)*((1/sqrt(2*3.1416))*exp(exp1)) st(i+1) = st(i) * exp(first_argument+second_argument) IF(st(i+1)<=20) THEN stmean(i+1) = 0.0 st(i+1) = st(i) else stmean(i+1) = st(i+1) ENDIF PRINT *,i+2,' ',stmean(i+1) mean = mean+stmean(i+1) END DO ! Output results uci = mean+(1.96*(segma/sqrt(n))) lci = mean-(1.96*(segma/sqrt(n))) PRINT *,'95% Confidence Interval for ', n, ' trials is between ', lci, ' and ', uci PRINT *,'' END PROGRAM SOLUTION

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• Mixing together Connect by, inner join and sum with Oracle

  - by François

  Hey there, I need help with a oracle query. Excuse me in advance for my english. Here is my setup: I have 2 tables called respectively "tasks" and "timesheets". The "tasks" table is a recursive one, that way each task can have multiple subtasks. Each timesheet is associated with a task (not necessarily the "root" task) and contains the number of hours worked on it. Example: Tasks id:1 | name: Task A | parent_id: NULL id:2 | name: Task A1 | parent_id: 1 id:3 | name: Task A1.1 | parent_id: 2 id:4 | name: Task B | parent_id: NULL id:5 | name: Task B1 | parent_id: 4 Timesheets id:1 | task_id: 1 | hours: 1 id:2 | task_id: 2 | hours: 3 id:3 | task_id:3 | hours: 1 id:5 | task_id:5 | hours:1 ... What I want to do: I want a query that will return the sum of all the hours worked on a "task hierarchy". If we take a look at the previous example, It means I would like to have the following results: task A - 5 hour(s) | task B - 1 hour(s) At first I tried this SELECT TaskName, Sum(Hours) "TotalHours" FROM ( SELECT replace(sys_connect_by_path(decode(level, 1, t.name), '~'), '~') As TaskName, ts.hours as hours FROM tasks t INNER JOIN timesheets ts ON t.id=ts.task_id START WITH PARENTOID=-1 CONNECT BY PRIOR t.id = t.parent_id ) GROUP BY TaskName Having Sum(Hours) > 0 ORDER BY TaskName And it almost work. THe only problem is that if there are no timesheet for a root task, it will skip the whole hieararchy... but there might be timesheets for the child rows and it is exactly what happens with Task B1. I know it is the "inner join" part that is causing my problem but I'm not sure how can I get rid of it. Any idea how to solve this problem? Thank you

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• In Javascript, what's better than try/catch for exiting an outer scope?

  - by gruseom

  In Javascript, I sometimes want to return a value from a scope that isn't the current function. It might be a block of code within the function, or it might be an enclosing function as in the following example, which uses a local function to recursively search for something. As soon as it finds a solution, the search is done and the whole thing should just return. Unfortunately, I can't think of a simpler way to do this than by hacking try/catch for the purpose: function solve(searchSpace) { var search = function (stuff) { solution = isItSolved(stuff); if (solution) { throw solution; } else { search(narrowThisWay(stuff)); search(narrowThatWay(stuff)); }; }; try { return search(searchSpace); } catch (solution) { return solution; }; }; I realize one could assign the solution to a local variable and then check it before making another recursive call, but my question is specifically about transfer of control. Is there a better way than the above? Perhaps involving label/break?

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• How to parse a string (by a "new" markup) with R ?

  - by Tal Galili

  Hi all, I want to use R to do string parsing that (I think) is like a simplistic HTML parsing. For example, let's say we have the following two variables: Seq <- "GCCTCGATAGCTCAGTTGGGAGAGCGTACGACTGAAGATCGTAAGGtCACCAGTTCGATCCTGGTTCGGGGCA" Str <- ">>>>>>>..>>>>........<<<<.>>>>>.......<<<<<.....>>>>>.......<<<<<<<<<<<<." Say that I want to parse "Seq" According to "Str", by using the legend here Seq: GCCTCGATAGCTCAGTTGGGAGAGCGTACGACTGAAGATCGTAAGGtCACCAGTTCGATCCTGGTTCGGGGCA Str: >>>>>>>..>>>>........<<<<.>>>>>.......<<<<<.....>>>>>.......<<<<<<<<<<<<. | | | | | | | || | +-----+ +--------------+ +---------------+ +---------------++-----+ | Stem 1 Stem 2 Stem 3 | | | +----------------------------------------------------------------+ Stem 0 Assume that we always have 4 stems (0 to 3), but that the length of letters before and after each of them can very. The output should be something like the following list structure: list( "Stem 0 opening" = "GCCTCGA", "before Stem 1" = "TA", "Stem 1" = list(opening = "GCTC", inside = "AGTTGGGA", closing = "GAGC" ), "between Stem 1 and 2" = "G", "Stem 2" = list(opening = "TACGA", inside = "CTGAAGA", closing = "TCGTA" ), "between Stem 2 and 3" = "AGGtC", "Stem 3" = list(opening = "ACCAG", inside = "TTCGATC", closing = "CTGGT" ), "After Stem 3" = "", "Stem 0 closing" = "TCGGGGC" ) I don't have any experience with programming a parser, and would like advices as to what strategy to use when programming something like this (and any recommended R commands to use). What I was thinking of is to first get rid of the "Stem 0", then go through the inner string with a recursive function (let's call it "seperate.stem") that each time will split the string into: 1. before stem 2. opening stem 3. inside stem 4. closing stem 5. after stem Where the "after stem" will then be recursively entered into the same function ("seperate.stem") The thing is that I am not sure how to try and do this coding without using a loop. Any advices will be most welcomed.

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• MySql stored procedure not found in PHP

  - by kaupov

  Hello, I have a trouble with MySql stored procedure that calls itself recursively using PHP (CakePHP). Calling it I receive following error: SQL Error: 1305: FUNCTION dbname.GetAdvertCounts does not exist The procedure itself is following: delimiter // DROP PROCEDURE IF EXISTS GetAdvertCounts// CREATE PROCEDURE GetAdvertCounts(IN category_id INT) BEGIN DECLARE no_more_sub_categories, advert_count INT DEFAULT 0; DECLARE sub_cat_id INT; DECLARE curr_sub_category CURSOR FOR SELECT id FROM categories WHERE parent_id = category_id; DECLARE CONTINUE HANDLER FOR NOT FOUND SET no_more_sub_categories = 1; SELECT COUNT(*) INTO advert_count FROM adverts WHERE category_id = category_id; OPEN curr_sub_category; FETCH curr_sub_category INTO sub_cat_id; REPEAT SELECT advert_count + GetAdvertCounts(sub_cat_id) INTO advert_count; FETCH curr_sub_category INTO sub_cat_id; UNTIL no_more_sub_categories = 1 END REPEAT; CLOSE curr_sub_category; SELECT advert_count; END // delimiter ; If I remove or comment out the recursive call, the procedure is working. Any idea what I'm missing here? The categories are 2 level deep.

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• Does using functional languages help against computing values repeatedly?

  - by sharptooth

  Consider a function f(x,y): f(x,0) = x*x; f(0,y) = y*(y + 1); f(x,y) = f(x,y-1) + f(x-1,y); If one tries to implement that recursively in some language like C++ he will encounter a problem. Suppose the function is first called with x = x0 and y = y0. Then for any pair (x,y) where 0 <= x < x0 and 0 <= y < y0 the intermediate values will be computed multiple times - recursive calls will form a huge tree in which multiple leaves will in fact contain the same pairs (x,y). For pairs (x,y) where x and y are both close to 0 values will be computed numerous times. For instance, I tested a similar function implemented in C++ - for x=20 and y=20 its computation takes about 4 hours (yes, four Earth hours!). Obviously the implementation can be rewritten in such way that repeated computation doesn't occur - either iteratively or with a cache table. The question is: will functional languages perform any better and avoid repeated computations when implementing a function like above recursively?

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• Return multiple IDs from a function and use the result in a query

  - by NewK

  I have this function that returns me all children of a tree node: CREATE OR REPLACE FUNCTION fn_category_get_childs_v2(id_pai integer) RETURNS integer[] AS $BODY$ DECLARE ids_filhos integer array; BEGIN SELECT array ( SELECT category_id FROM category WHERE category_id IN ( (WITH RECURSIVE parent AS ( SELECT category_id , parent_id from category WHERE category_id = id_pai UNION ALL SELECT t.category_id , t.parent_id FROM parent INNER JOIN category t ON parent.category_id = t.parent_id ) SELECT category_id FROM parent WHERE category_id <> id_pai ) ) ) into ids_filhos; return ids_filhos; END; and I would like to use it in a select statement like this: select * from teste1_elements where category_id in (select * from fn_category_get_childs_v2(12)) I've also tried this way with the same result: select * from teste1_elements where category_id=any(select * from fn_category_get_childs_v2(12))) But I get the following error: ERROR: operator does not exist: integer = integer[] LINE 1: select * from teste1_elements where category_id in (select *... ^ HINT: No operator matches the given name and argument type(s). You might need to add explicit type casts. The function returns an integer array, is that the problem? SELECT * from fn_category_get_childs_v2(12) retrieves the following array (integer[]): '{30,32,34,20,19,18,17,16,15,14}'

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• User to be validated against nested security groups in Windows.

  - by user412272

  Hi, This is my first post here and after much looking around I have come here with my question. Will really appreciate a fast response. I am faced with a problem to validate user credentials of the currently logged on user against a group in Windows. The user membership to a group can be through other groups also ie nested membership. Eg. User U is a part of group G1. Group G1 is a part of another group G2. The requirement is that when the user is validated against group G2, the validations should succeed. The user can be a local or AD user but the group will always be a local group ( or domain local group if created directly on a DC). I have tried using WindowsPrincipal.IsInRole() method, but it seems to be checking only for direct membership to a group. I also tried UserPrincipal.GetAuthorizationGroups() for the current user, but it also doesnt seem to be doing recursive search. I am posting a code snippet of the working code below, but this code is taking much more than acceptable time. bool CheckUserPermissions(string groupName) { WindowsIdentity currentUserIdentity = System.Security.Principal.WindowsIdentity.GetCurrent(); bool found = false; PrincipalContext context= new PrincipalContext(ContextType.Machine); GroupPrincipal group = GroupPrincipal.FindByIdentity(context, IdentityType.Name, groupName); if (group!= null) { foreach (Principal p in group.GetMembers(true)) { if (p.Sid == currentUserIdentity.User) { found = true; break; } } group.Dispose(); } return found; }

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• Getting the Item Count of a large sharepoint list in fastest way

  - by sooraj

  I am trying to get the count of the items in a sharepoint document library programatically. The scale I am working with is 30-70000 items. We have usercontrol in a smartpart to display the count . Ours is a TEAM site. This is the code to get the total count SPList VoulnterrList = web.Lists[ListTitle]; SPQuery query = new SPQuery(); query.ViewAttributes = "Scope=\"Recursive\""; string queries = "<Where><Eq><FieldRef Name='ApprovalStatus' /><Value Type='Choice'>Pending</Value></Eq></Where>"; query.Query = queries; SPListItemCollection lstitemcollAssoID = VoulnterrList.GetItems(query); lblCount.Text = "Total Proofs: " + VoulnterrList.Items.Count.ToString() + " Pending Proofs: " + lstitemcollAssoID.Count.ToString(); The problem is this has serious performance issue it takes 75 to 80 sec to load the page. if we comment this page load will decrees to 4 sec. Any better approch for this problem Ours is sharepoint 2007

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• Best method to search heriarachal data

  - by WDuffy

  I'm looking at building a facility which allows querying for data with hierarchical filtering. I have a few ideas how I'm going to go about it but was wondering if there are any recommendations or suggestions that might be more efficient. As an example imagine that a user is searching for a job. The job areas would be as follows. 1: Scotland 2: --- West Central 3: ------ Glasgow 4: ------ Etc 5: --- North East 6: ------ Ayrshire 7: ------ Etc A user can search specific (ie Glasgow) or in a larger area (ie Scotland). The two approaches I am considering are 1: keep a note of children in the database for each record (ie cat 1 would have 2, 3, 4 in its children field) and query against that record with a SELECT * FROM Jobs WHERE Category IN Areas.childrenField. 2: Use a recursive function to find all results who have a relation to the selected area The problems I see from both are 1: holding this data in the db will mean having to keep track of all changes to structure 2: Recursion is slow and inefficent Any ideas, suggestion or recommendations on the best approach? I'm using C# ASP.NET with MSSQL 2005 DB.

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• Learning Python else syntax error

  - by user1441016

  Hi I am learning python by doing the practice problems for Open course at MIT 6.00 Intro to Computer Science. I am Trying to do practice problem 1 part 2 create a recursive function to count the instance of key in target. My code so far... from string import * def countSubStringMatchRecursive (target, key,x,s): if (find(target,key)==find(target,key,s)) and (find(target,key)==find(target,key,(find(target,key)))):#if first and last return (1) elif (find(target,key)==find(target,key,s))and (find(target,key)!=find(target,key,(find(target,key)))):#if first but not last x=1 s= find(target,key) return (countSubStringMatchRecursive(target,key,s,x) elif (find(target,key,s))==-1 and (find(target,key)!=find(target,key,s)):#if last but not first return (x+1) elif:(find(target,key,s))!=-1 and (find(target,key)!=find(target,key,s)):#if not last and not first x=x+1 s= find(target,key,s) return (countSubStringMatchRecursive(target,key,s,x) I getting a syntax error at line 8. I would just like to know what I did wrong there. Dont worry about the other mistakes I should be able to get those sorted out. I just Stuck on this. Thanks.

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• Handling text menu in Python

  - by PulpFiction

  Hi all. I am trying to create a text based menu in Python. Here is the code: #!/usr/bin/env python def testcaseOutput(): print '1. Add. 2. Subtract. 3. Divide. 4. Multiply' try: answer = int(raw_input('Enter a value (1 - 4) >. ')) except ValueError: print 'Invalid input. Enter a value between 1 -4 .' testcaseOutput() if answer in range(1, 5): return answer else: print 'Invalid input. Enter a value between 1 - 4.' testcaseOutput() My question: When the user enters an invalid input, i.e. not a number, I want this function to get called again. So I used the recursive approach which I think is bad design. I use that approach again in the if answer in range(1, 5). Is there any other way to handle this? I need the prompt called again when there is an invalid input. Also, is there any way I can club the two constraints: check whether input is a number and check whether the number is in the range(1,5) together? As you can see, I am checking that individually.

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• question about Ackermann function

  - by davit-datuashvili

  i am doing to write recursive program which calculates Ackemann function http://en.wikipedia.org/wiki/Ackermann_function here is code public class Ackermann{ public static long ackermann( long m,long n){ return (m==0)? n+1: (m>0 && n==0)? ackermann(m-1,1): (m>0 && n>0)? ackermann(m-1, ackermann(m,n-1)); } public static void main(String[]args){ long m=4; long n=2; System.out.println(ackermann(m,n)); } } but it shows me mistakes Ackermann.java:7: : expected (m>0 && n>0)? ackermann(m-1, ackermann(m,n-1)); ^ Ackermann.java:7: ';' expected (m>0 && n>0)? ackermann(m-1, ackermann(m,n-1)); ^ Ackermann.java:18: illegal start of expression public static void main(String[]args){ ^ Ackermann.java:18: ';' expected public static void main(String[]args){ ^ Ackermann.java:18: illegal start of expression public static void main(String[]args){ ^ Ackermann.java:18: ';' expected public static void main(String[]args){ ^ Ackermann.java:18: ';' expected public static void main(String[]args){ ^ Ackermann.java:26: reached end of file while parsing } ^ 8 errors please help

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• Java How to find a value in a linked list iteratively and recursively

  - by Roxy

  Hi I have a method that has a reference to a linked list and a int value. So, this method would count and return how often the value happens in the linked list. So, I decided to make a class, public class ListNode{ public ListNode (int v, ListNode n) {value = v; next = n;) public int value; public ListNode next; } Then, the method would start with a public static int findValue(ListNode x, int valueToCount){ // so would I do it like this?? I don't know how to find the value, // like do I check it? for (int i =0; i< x.length ;i++){ valueToCount += valueToCount; } So, I CHANGED this part, If I did this recursively, then I would have public static int findValue(ListNode x, int valueToCount) { if (x.next != null && x.value == valueToCount { return 1 + findValue(x, valueToCount);} else return new findvalue(x, valueToCount); SO, is the recursive part correct now?

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• OutOfMemoryError creating a tree recursively?

  - by Alexander Khaos Greenstein

  root = new TreeNode(N); constructTree(N, root); private void constructTree(int N, TreeNode node) { if (N > 0) { node.setLeft(new TreeNode(N-1)); constructTree(N-1, node.getLeft()); } if (N > 1) { node.setMiddle(new TreeNode(N-2)); constructTree(N-2, node.getMiddle()); } if (N > 2) { node.setRight(new TreeNode(N-3)); constructTree(N-3, node.getRight()); } Assume N is the root number, and the three will create a left middle right node of N-1, N-2, N-3. EX: 5 / | \ 4 3 2 /|\ 3 2 1 etc. My GameNode class has the following variables: private int number; private GameNode left, middle, right; Whenever I construct a tree with an integer greater than 28, I get a OutOfMemoryError. Is my recursive method just incredibly inefficient or is this natural? Thanks!

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• directory traversal in Java using different regular and enhanced for loops

  - by user3245621

  I have this code to print out all directories and files. I tried to use recursive method call in for loop. With enhanced for loop, the code prints out all the directories and files correctly. But with regular for loop, the code does not work. I am puzzled by the difference between regular and enhanced for loops. public class FileCopy { private File[] childFiles = null; public static void main(String[] args) { FileCopy fileCopy = new FileCopy(); File srcFile = new File("c:\\temp"); fileCopy.copyTree(srcFile); } public void copyTree(File file){ if(file.isDirectory()){ System.out.println(file + " is a directory. "); childFiles = file.listFiles(); /*for(int j=0; j<childFiles.length; j++){ copyTree(childFiles[j]); } This part is not working*/ for(File a: childFiles){ copyTree(a); } return; } else{ System.out.println(file + " is a file. "); return; } } }

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