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• Using Closure Properties to prove Regularity

  - by WATWF

  Here's a homework problem: Is L_4 Regular? Let L_4 = L*, where L={0^i1^i | i>=1}. I know L is non-regular and I know that Kleene Star is a closed operation, so my assumption is that L_4 is non-regular. However my professor provided an example of the above in which L = {0^p | p is prime}, which he said was regular by proving that L* was equal to L(000* + e) by saying each was a subset of one another (e in this case means the empty word). So his method involved forming a regex of 0^p, but how I can do that when I essentially have one already?

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• Why MySQL multiple-column index is overpopulated?

  - by actual

  Consider following MySQL table: CREATE TABLE `log` ( `what` enum('add', 'edit', 'remove') CHARACTER SET ascii COLLATE ascii_bin NOT NULL, `with` int(10) unsigned NOT NULL, KEY `with_what` (`with`,`what`) ) ENGINE=InnoDB; INSERT INTO `log` (`what`, `with`) VALUES ('add', 1), ('edit', 1), ('add', 2), ('remove', 2); As I understand, with_what index must have 2 unique entries on its first with level and 3 unique entries in what "subindex". But MySQL reports 4 unique entries for each level. In other words, number of unique elements for each level is always equal to number of rows in log table. Is that a bug, a feature or my misunderstanding?

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• how to interleaving lists

  - by user2829177

  I have two lists that could be not equal in lengths and I want to be able to interleave them. I want to be able to append the extra values in the longer list at the end of my interleaved list.I have this: a=xs b=ys minlength=[len(a),len(b)] extralist= list() interleave= list() for i in range((minval(minlength))): pair=a[i],b[i] interleave.append(pair) flat=flatten(interleave) c=a+b if len(b)>len(a): remainder=len(c)-len(a) for j in range(-remainder): extra=remainder[j] extralist.append(extra) if len(a)>len(b): remainder=len(c)-len(b) for j in range(-remainder): extra=remainder[j] final=flat+extralist return final but if I test it: >>> interleave([1,2,3], ["hi", "bye",True, False, 33]) [1, 'hi', 2, 'bye', 3, True] >>> The False and 33 don't appear. What is it that Im doing wrong?

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• How to hash and check for equality of objects with circular references

  - by mfya

  I have a cyclic graph-like structure that is represented by Node objects. A Node is either a scalar value (leaf) or a list of n=1 Nodes (inner node). Because of the possible circular references, I cannot simply use a recursive HashCode() function, that combines the HashCode() of all child nodes: It would end up in an infinite recursion. While the HashCode() part seems at least to be doable by flagging and ignoring already visited nodes, I'm having some troubles to think of a working and efficient algorithm for Equals(). To my surprise I did not find any useful information about this, but I'm sure many smart people have thought about good ways to solve these problems...right? Example (python): A = [ 1, 2, None ]; A[2] = A B = [ 1, 2, None ]; B[2] = B A is equal to B, because it represents exactly the same graph. BTW. This question is not targeted to any specific language, but implementing hashCode() and equals() for the described Node object in Java would be a good practical example.

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• C++ Segementation fault in binary_function

  - by noryb009

  I'm using Visual Studio 2010 Beta 2 (also tried with NetBeans), and I'm having a segmentation fault in the following code: // One of the @link s20_3_3_comparisons comparison functors@endlink. template <class _Tp> struct less : public binary_function<_Tp, _Tp, bool> { bool operator()(const _Tp& __x, const _Tp& __y) const { return __x < __y; } //this is the problem line }; I don't know what in my program calls it, but I am trying to find out. (I think it's a map) Does anyone know what to do, or has encountered this before?

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• What Can A 'TreeDict' (Or Treemap) Be Used For In Practice?

  - by Seun Osewa

  I'm developing a 'TreeDict' class in Python. This is a basically a dict that allows you to retrieve its key-value pairs in sorted order, just like the Treemap collection class in Java. I've implemented some functionality based on the way unique indexes in relational databases can be used, e.g. functions to let you retrieve values corresponding to a range of keys, keys greater than, less than or equal to a particular value in sorted order, strings or tuples that have a specific prefix in sorted order, etc. Unfortunately, I can't think of any real life problem that will require a class like this. I suspect that the reason we don't have sorted dicts in Python is that in practice they aren't required often enough to be worth it, but I want to be proved wrong. Can you think of any specific applications of a 'TreeDict'? Any real life problem that would be best solved by this data structure? I just want to know for sure whether this is worth it.

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• new with exception with Microsoft

  - by wsd

  As I'm coding for both Windows and Linux, I have a whole host of problems. Microsoft Visual C++ has no stdint header, but for that I wrote my own. Now I found out that MS C++'s new operator does not throw an exception, so I want to fix this a quickly as possible. I know I can define a Macro with Parameters in Parenthesis, can I define a macro that replaces MyClass x = new MyClass(); with #ifdef MSC_VER if(!(MyClass x = new MyClass()) { throw new std::bad_alloc(); } #else MyClass x = new MyClass(); #endif (or something equivalent), AND works in BOTH MS C++ and G++ ? Or alternatively if that is not possible, a batch file to run over the Code to do this? I have become rather dependent on this exception being thrown.

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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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• MySQL Join issue

  - by mouthpiec

  Hi, I have the following tables: --table sportactivity-- sport_activity_id, home_team_fk, away_team_fk, competition_id_fk, date, time (tuple example) - 1, 33, 41, 5, 2010-04-14, 05:40:00 --table teams-- team_id, team_name (tuple example) - 1, Algeria Now I have the following SQL statment that I use to extract Team A vs Team B SELECT sport_activity_id, T1.team_name AS TeamA, T2.team_name AS TeamB, DATE_FORMAT( DATE, '%d/%m/%Y' ) AS DATE, DATE_FORMAT( TIME, '%H:%i' ) AS TIME FROM sportactivity JOIN teams T1 ON home_team_fk = T1.team_id JOIN teams T2 ON ( away_team_fk = T2.team_id OR away_team_fk = '0' ) WHERE DATE( DATE ) >= CURDATE( ) ORDER BY DATE( DATE ) My problem is that when team B is empty, I am having irrelevant information .... it seems that it is returning all the combinations. I need a query that when team B is equal to 0, (this can occur in my scenario) I get only Team A - Team B (as 0) once.

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• C++ Word-Number to int

  - by Andrew

  I'm developing a program that makes basic calculations using words instead of numbers. E.g. five + two would output seven. The program becomes more complex, taking input such as two_hundred_one + five_thousand_six (201 + 5006) Through operator overloading methods, I split each number and assign it to it's own array index. two would be [0], hundred is [1], and one is [2]. Then the array recycles for 5006. My problem is, to perform the actual calculation, I need to convert the words stored in the array to actual integers. I have const string arrays such as this as a library of the words: const string units[] = { "", "one", "two", "three", "four", "five", "six", "seven", "eight", "nine" }; const string teens[] = { "ten", "eleven", "twelve", "thirteen", "fourteen", "fifteen", "sixteen", "seventeen", "eighteen", "nineteen" }; const string tens[] = { "", "", "twenty", "thirty", "forty", "fifty", "sixty", "seventy", "eighty", "ninety" }; If my 'token' array has stored in it two hundred one in index 0, 1, and 2, I'm not sure what the best way to convert these to ints would involve.

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• Why do the following expanded if shorthand statements not work in javascript?

  - by PeanutsMonkey

  This is my first attempt to write shorthand if statements however am befuddled by why the expanded versions don't work quite the way I imagined they would. Code 1 - Does not work if(document.getElementById == true) { alert("The document object model is supported by: " + navigator.appName); } Code 2 - Does work if(document.getElementById != false) { alert("The document object model is supported by: " + navigator.appName); } Code 3 - The shorthand that does work if(document.getElementById) { alert("The document object model is supported by: " + navigator.appName); } Why is that if I expand the shorthand in 3 to the first code sample not work and why does it work if I have it equal to != false?

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• Insert error when sending post array to activerecord

  - by Gonzalo

  I am using CodeIgniter + phpActiveRecord. I am getting all the records from the $_POST array and I want to send that same array to my activeRecord class to insert the data into the DB. This line doesn't seem to be working but I can't get the error because the page is just blank: Car::create($this->input->post()); If the names of the fields are equal to the names of the columns in the table, should it what I pasted above work? ==========SOLVED======== It is possible to do it, and in the model of the object one can add var $name_of_the_field_which_you_don't_process = FALSE; And that's it.

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• C++ Segmentation fault in binary_function

  - by noryb009

  I'm using Visual Studio 2010 Beta 2 (also tried with NetBeans), and I'm having a segmentation fault in the following code: // One of the @link s20_3_3_comparisons comparison functors@endlink. template <class _Tp> struct less : public binary_function<_Tp, _Tp, bool> { bool operator()(const _Tp& __x, const _Tp& __y) const { return __x < __y; } //this is the problem line }; I don't know what in my program calls it, but I am trying to find out. (I think it's a map) Does anyone know what to do, or has encountered this before?

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• How do I create a set with std::pair thats sorted based on the ::second pair member using bind

  - by Stone Free

  I know I could use the following: template <typename Pair> struct ComparePairThroughSecond : public std::unary_function<Pair, bool> { bool operator ()(const Pair& p1, const Pair& p2) const { return p1.second < p2.second; } }; std::set<std::pair<int, long>, ComparePairThroughSecond> somevar; but wondered if it could be done with boost::bind

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• help implementing algorithm

  - by davit-datuashvili

  http://en.wikipedia.org/wiki/All_nearest_smaller_values this is site of the problem and here is my code but i have some trouble to implement it import java.util.*; public class stack{ public static void main(String[]args){ int x[]=new int[]{ 0, 8, 4, 12, 2, 10, 6, 14, 1, 9, 5, 13, 3, 11, 7, 15 }; Stack<Integer> st=new Stack<Integer>(); for (int a:x){ while (!st.empty() && st.pop()>=a){ System.out.println( st.pop()); if (st.empty()){ break; } else{ st.push(a); } } } } } and here is pseudo code from site S = new empty stack data structure for x in the input sequence: while S is nonempty and the top element of S is greater than or equal to x: pop S if S is empty: x has no preceding smaller value else: the nearest smaller value to x is the top element of S push x onto S

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• PHP code in drupal pages treating > as ?>

  - by AmaDaden

  While working on an existing Drupal site I've noticed a strange glitch that causes any PHP operator with in it to act like a ? tag. This is happening in in Drupal pages that I create that have a 'Input Format' of 'PHP code'. For example this line of code foreach($array as $key = $value){ results in a very broken page that prints out $value){ Does any one know what could be causing this? My Dev environment is XAMPP. Drupal version is 6.15. PHP version is 5.2.9.

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• DJANGO complex modelling

  - by SledgehammerPL

  Hello. I have such model now: receipt contains components. component contain product. The difference between component and product is, that component has quantity and measure unit: eg. component is 100g sugar - sugar is a product. So I need to make lots of components to satisfy different recipes - 100g sugar is not equal 200g sugar I wonder if I can remodel it to kick off components - in pure sql it's rather easy, but I'm trying to USE django - not making workarounds. class Receipt(models.Model): name = models.CharField(max_length=128) (...) components = models.ManyToManyField(Component) class Component(models.Model): quantity = models.FloatField(max_length=9) unit = models.ForeignKey(Unit) product = models.ForeignKey(Product) class Product(models.Model): name = models.CharField(max_length = 128) TIA

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• T-SQL Operations on a Calculated Date Field

  - by firedrawndagger

  Can I do WHERE operations on a calculated date field? I have a lookup field, which has been written badly in SQL and unfortunately I can't change it. But basically it stores dates as characters such as "July-2010" or "June-2009" (along with other non date data). I want to extract the dates first (which I did using a LIKE opertor) and then extract data based on a date range. SELECT BusinessUnit, Lookup, ReleaseDate FROM ( SELECT TOP 10 LookupColumn As Lookup, BU as BusinessUnit, CONVERT(DATETIME, REPLACE(LookupColumn,'-',' ')) as ReleaseDate FROM [dbo].[LookupTable] WHERE LookupColumn LIKE N'%-2010' ) MyTable ORDER BY ReleaseDate WHERE ReleaseDate = '2010-02-01' I'm having issues with WHERE operator. I would assume creating a subquery to encapsulate the calculated field would allow me to do operations with it such as WHERE but maybe I'm wrong. Bottom line is it possible to do operations on calculated fields?

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• How to show a page after a specific time period?

  - by Mahfuz

  I want to build an online quiz test site. Suppose, exam will start at 10:00 am and a student login to give exam at 9:45 am. Whenever the student clicks 'Take Exam' button, he/she cannot not get access to the question paper because the exam time is 10:00 am and there are still 15 minutes before the exam start. Now I want to put some Javascript or PHP code that will prohibit the students to give exam earlier and if a students come early, it will show a stopwatch which display the remaining time before exam time and when the current time is equal to exam time then he/she will be directly redirected to the question paper page.

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• Query filter design for string field

  - by Midhat

  A field in my table can have arbitrary strings. On the UI, there is a drop down having options like All, Value1, Value2 And the results were filtered by the selected option value. So far this is easy and adding new filters to the UI is not a problem. Needs no changes in my stored procedure. Now I want to have an "Others" option here as well, which will return rows not having the column value as Value1 or Value2. Apparently this will require a "not in" operator in my query, and will make maintenance difficult, as the list of values is likely to change Any suggestions, design tips?

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• Is it possible to apply inheritance to a Singleton class?

  - by Bragaadeesh

  Hi, Today I faced one question in interview. Is it possible to apply inheritance concept on Singleton Classes. I said since the constructor is private, we cannot extend that Singleton class (can someone please validate this). Next thing he asked me is to apply inheritance on that Singleton class. So, I made the Singleton's constructor as protected thinking that child's constructor also has be protected. But I was wrong the child can have a modifier either equal to or higher than that. So, I asked him to give a real world example on such a case. He was not able to give me one and said that I cant ask questions and wanted me to tell whether this scenario is possible or not. I went kind of blank. My question here is, Is this possible? Even if its possible, what is the use of it? What real world scenario would demand such a use. Thanks

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• Why does a Linq Cast<T> operation fail when I have an implicit cast defined?

  - by Ryan Versaw

  I've created two classes, with one of them having an implicit cast between them: public class Class1 { public int Test1; } public class Class2 { public int Test2; public static implicit operator Class1(Class2 item) { return new Class1{Test1 = item.Test2}; } } When I create a new list of one type and try to Cast<T> to the other, it fails with an InvalidCastException: List<Class2> items = new List<Class2>{new Class2{Test2 = 9}}; foreach (Class1 item in items.Cast<Class1>()) { Console.WriteLine(item.Test1); } This, however, works fine: foreach (Class1 item in items) { Console.WriteLine(item.Test1); } Why is the implicit cast not called when using Cast<T>?

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• MySQL Query WHERE Including CASE or IF?

  - by handfix

  Strange problem. My Query looks like SELECT DISTINCT ID, `etcetc`, `if/elses over muliple joined tables` FROM table1 AS `t1` # some joins, eventually unrelated in that context WHERE # some standard where statements, they work/ CASE WHEN `t1`.`field` = "foo" THEN (`t1`.`anOtherField` != 123 AND `t1`.`anOtherField` != 456 AND `t1`.`anOtherOtherField` != "some String") WHEN `t1`.`field` = "bar" THEN `t1`.`aSecondOtherField` != 12345 END #ORDER BY CASE etc. Standard Stuff Apperantly MySQL returns a wrong rowcount and I think my problem is in the logic of the WHERE ... CASE statement. Maybe with the brackets? Maybe I should go for operator OR and not AND? Should my the second WHEN include brackets also, even when I only compare one field? Should I use IF and not CASE? Basically I want to exclude some rows with specific values IF theres a specific value in field foo or bar I would try that all out, but it takes a huge amount of time to complete that query... :(

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• How to force a deep copy when copying structs with arrays?

  - by Danvil

  If have a struct A { public double[] Data; public int X; } How can I force a deep copy when using operator= or adding instances of A to a container? The problem is for example: A a = new A(); var list = new List<A>(); list.Add(a); // does not make a deep copy of Data A b = a; // does not make a deep copy of Data Do I really have to implement my own DeepClone method and call it every time? This would be extremly error-prone ...

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• Dynamic name of NSMutableDictionary?

  - by Bruno

  Hi everyone I load from a txt file many info, and I would like, if possible, to dynamically create NSmutable dictionary with the elements of the txt. For example, each is like that: id of element | date | text What I'm asking is the equivalent of the NSString stringWithFormat:. Can we do the same for an Mutable Dictionary? To be more practical, let's say the NSString *date is equal to "23/12/2009" (for europe). I want to create a dictionary called 23/12/2009 without declaring *23/12/2009 but just something like dictionaryWithFormat: @"%@", date]; I'm stuck on this, and I don't even know if it is possible. If not, what's the best way to approach that? Thanks everyone Regards

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