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  • What is the time complexity of LinkedList.getLast() in Java?

    - by i.
    I have a private LinkedList in a Java class & will frequently need to retrieve the last element in the list. The lists need to scale, so I'm trying to decide whether I need to keep a reference to the last element when I make changes (to achieve O(1)) or if the LinkedList class does that already with the getLast() call. What is the big-O cost of LinkedList.getLast() and is it documented? (i.e. can I rely on this answer or should I make no assumptions & cache it even if it's O(1)?)

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  • What does `?` stand for in SQL?

    - by user295189
    I have this SQL by a programmer: $sql = " INSERT INTO `{$database}`.`table` ( `my_id`, `xType`, `subType`, `recordID`, `textarea` ) VALUES ( {$my_id}, ?xType, ?subType, {$recordID}, ?areaText ) "; My question is why is he using ? before values? How do I see what values are coming in? I did echo and it shows ?xType as ?xType. No values. What does ? stand for in SQL?

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  • how does array_diff work?

    - by SpawnCxy
    I just wonder how array_diff() works.And obviously it couldn't work as follows function array_diff($arraya, $arrayb) { $diffs = array(); foreach ($arraya as $keya => $valuea) { foreach ($arrayb as $valueb) { if ($valuea == $valueb) { break; } $diffs[$keya]=$valuea; } } return $diffs; } //couldn't be worse than this Hope someone can show me some better solution. Thanks.

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  • How to set up a specific registration on Database

    - by ymorenz
    I'm creating a database so I can access names of people from a university. But I would like to create a registration ID for each person like 1012607, of which the first 2 numbers would be the year (11 for 2011) and the third digit would be the semester they registered (1 in the beginning of the year and 2 in the end of the year). The other 4 digits would be incremental. I don't know how to code a prefixed number in MySQL that can change only the last 4 digits and after a year change the first 2 digits every time you have a new registration. Can someone please help me?

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  • SQL query doesn't get inserted

    - by Deejdd
    I've been trying to get my query to work for some time it runs but doesn't insert anything nor does it return any errors. The database connection is open and is successfuly connection. The Table is called errorlog and holds the following data - id (int autoincremental, Primary key, Unique) - exception (varchar) - time (DateTime) exception = String(error message) time = DateTime.Now Here's the code: public void insertError(string error, DateTime time) { SqlCeParameter[] sqlParams = new SqlCeParameter[] { new SqlCeParameter("@exception", error), new SqlCeParameter("@time", time) }; try { cmd = new SqlCeCommand(); cmd.Connection = connection; cmd.CommandType = CommandType.Text; cmd.CommandText = "INSERT INTO errorlog (exception, time) VALUES(@exception, @time)"; cmd.Parameters.AddRange(sqlParams); cmd.ExecuteNonQuery(); } catch (Exception e) { Console.WriteLine(e.Message); } } Any help would be appreciated, Thanks in advance. EDIT Removed quotes around @exception Heres the connection: protected DataController() { try { string appPath = System.IO.Path.GetDirectoryName(Assembly.GetAssembly(typeof(DataController)).CodeBase).Replace(@"file:\", "") + @"\"; string strCon = @"Data Source = " + appPath + @"Data\EasyShop.sdf"; connection = new SqlCeConnection(strCon); } catch (Exception e) { } connection.Open(); } Finally the way it gets called: public bool log(string msg, bool timestamp = true) { DataController dc = DataController.Instance(); dc.insertError(msg, DateTime.Today); return true; }

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  • F# why my recursion is faster than Seq.exists?

    - by user38397
    I am pretty new to F#. I'm trying to understand how I can get a fast code in F#. For this, I tried to write two methods (IsPrime1 and IsPrime2) for benchmarking. My code is: // Learn more about F# at http://fsharp.net open System open System.Diagnostics #light let isDivisible n d = n % d = 0 let IsPrime1 n = Array.init (n-2) ((+) 2) |> Array.exists (isDivisible n) |> not let rec hasDivisor n d = match d with | x when x < n -> (n % x = 0) || (hasDivisor n (d+1)) | _ -> false let IsPrime2 n = hasDivisor n 2 |> not let SumOfPrimes max = [|2..max|] |> Array.filter IsPrime1 |> Array.sum let maxVal = 20000 let s = new Stopwatch() s.Start() let valOfSum = SumOfPrimes maxVal s.Stop() Console.WriteLine valOfSum Console.WriteLine("IsPrime1: {0}", s.ElapsedMilliseconds) ////////////////////////////////// s.Reset() s.Start() let SumOfPrimes2 max = [|2..max|] |> Array.filter IsPrime2 |> Array.sum let valOfSum2 = SumOfPrimes2 maxVal s.Stop() Console.WriteLine valOfSum2 Console.WriteLine("IsPrime2: {0}", s.ElapsedMilliseconds) Console.ReadKey() IsPrime1 takes 760 ms while IsPrime2 takes 260ms for the same result. What's going on here and how I can make my code even faster?

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  • How much faster is C++ than C#?

    - by Trap
    Or is it now the other way around? From what I've heard there are some areas in which C# proves to be faster than C++, but I've never had the guts to test it by myself. Thought any of you could explain these differences in detail or point me to the right place for information on this.

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  • SQL - Query to display average as either "longer than" or "shorter than"

    - by user1840801
    Here are the tables I've created: CREATE TABLE Plane_new (Pnum char(3), Feature varchar2(20), Ptype varchar2(15), primary key (Pnum)); CREATE TABLE Employee_new (eid char(3), ename varchar(10), salary number(7,2), mid char(3), PRIMARY KEY (eid), FOREIGN KEY (mid) REFERENCES Employee_new); CREATE TABLE Pilot_new (eid char(3), Licence char(9), primary key (eid), foreign key (eid) references Employee_new on delete cascade); CREATE TABLE FlightI_new (Fnum char(4), Fdate date, Duration number(2), Pid char(3), Pnum char(3), primary key (Fnum), foreign key (Pid) references Pilot_new (eid), foreign key (Pnum) references Plane_new); And here is the query I must complete: For each flight, display its number, the name of the pilot who implemented the flight and the words ‘Longer than average’ if the flight duration was longer than average or the words ‘Shorter than average’ if the flight duration was shorter than or equal to the average. For the column holding the words ‘Longer than average’ or ‘Shorter than average’ make a header Length. Here is what I've come up with - with no luck! SELECT F.Fnum, E.ename, CASE Length WHEN F.Duration>(SELECT AVG(F.Duration) FROM FlightI_new F) THEN "Longer than average" WHEN F.Duration<=(SELECT AVG(F.Duration) FROM FlightI_new F) THEN 'Shorter than average' END FROM FlightI_new F LEFT OUTER JOIN Employee_new E ON F.Pid=E.eid GROUP BY F.Fnum, E.ename; Where am I going wrong?

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  • Problem with mysql_query() ;Says resource expected .

    - by user364651
    I have this php file. The lines marked as bold are showing up the error :"mysql_query() expecets parameter 2 to be a resources. Well, the similar syntax on the line on which I have commented 'No error??' is working just fine. function checkAnswer($answerEntered,$quesId) { //This functions checks whether answer to question having ques_id = $quesId is satisfied by $answerEntered or not $sql2="SELECT keywords FROM quiz1 WHERE ques_id=$quesId"; **$result2=mysql_query($sql2,$conn);** $keywords=explode(mysql_result($result2,0)); $matches=false; foreach($keywords as $currentKeyword) { if(strcasecmp($currentKeyword,$answerEntered)==0) { $matches=true; } } return $matches; } $sql="SELECT answers FROM user_info WHERE user_id = $_SESSION[user_id]"; $result=mysql_query($sql,$conn); // No error?? $answerText=mysql_result($result,0); //Retrieve answers entered by the user $answerText=str_replace('<','',$answerText); $answerText=str_replace('>',',',$answerText); $answerText=substr($answerText,0,(strlen($answerText)-1)); $answers=explode(",",$answerText); //Get the questions that have been assigned to the user. $sql1="SELECT questions FROM user_info WHERE user_id = $_SESSION[user_id]"; **$result1=mysql_query($sql1,$conn);** $quesIdList=mysql_result($result1,0); $quesIdList=substr($quesIdList,0,(strlen($quesIdList)-1)); $quesIdArray=explode(",",$quesIdList); $reportCard=""; $i=0; foreach($quesIdArray as $currentQuesId) { $answerEnteredByUser=$answers[$i]; if(checkAnswer($answerEnteredByUser,$currentQuesId)) { $reportCard=$reportCard+"1"; } else { $reportCard=$reportCard+"0"; } $i++; } echo $reportCard; ?> Here is the file connect.php. It is working just fine for other PHP documents. <?php $conn= mysql_connect("localhost","root","password"); mysql_select_db("quiz",$conn); ?>

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  • SELECT DISTINCT multiple field search?

    - by Patrick
    I'm trying to search multiple fields zc_city and zc_zip for when user input and then return row results for zc_city zc_state and zc_zip $q = strtolower($_GET["q"]); if (!$q) return; $sql = "SELECT DISTINCT zc_city AS zcity FROM search_zipcodes WHERE zc_city LIKE '$q%'"; $rsd = mysql_query($sql); while($rs = mysql_fetch_array($rsd)) { $zcity = $rs['zcity']; echo "$zcity\n"; }

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  • PHP - Get value of imput box, without a form?

    - by Dodi300
    Hello. Does anyone know how I can get the value of an imput box, without having a form? I want a sumbit button, but instead of submiting a form, I want it to change data in a MySQL database. Something like this maybe? $img1="WHAT DO I PUT HERE?" $idx=1 $sql="INSERT INTO games SET img1='$img1' WHERE id=$idx"; $result=mysql_query($sql); Could I use that code on a "onclick" event? The imput box is named "img1". Thanks for the help!

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  • Detecting when Javascript is performing poorly

    - by what-the-crap
    I'm working on a webapp in jquery that, on older machines or machines without much resources, may perform poorly. To get around this I'd like to make a degraded version that disables some of the features, particularly those that rely on large images. How can I tell if my app is running poorly on the user's computer in jquery or javascript in general? I just need a way to call a function that will degrade the app. (especially when the user may run low on system memory) The only way I can think of is for manual user intervention, but the option would add clutter for users that don't need it and users that do need it may not notice it. Thanks!

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  • Which of these queries is more efficient?

    - by Brian
    Which of these queries are more efficient? select 1 as newAndClosed from sysibm.sysdummy1 where exists ( select 1 from items where new = 1 ) and not exists ( select 1 from status where open = 1 ) select 1 as newAndClosed from items where new = 1 and not exists ( select 1 from status where open = 1 )

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  • Updating multiple rows with an array

    - by Copephobia
    I have a table that holds user information. One of the columns holds the position of the user in the game they are in. When a game is being created, I need to update the positions of the users of each team. Here is an example: Game id : 7 Team 1 users : 1,2 Team 2 users : 3,4 team1_position : array(1,2) team2_position : array(13,14) What I want to do is update the user table using the array of positions in the SET area. My goal is to be able to update the users without the need for their id (I have different size game boards, so I have multiple position arrays for each board size) How can I do something like this: UPDATE user SET position='(team1_position)' WHERE game = '7' AND team = '1' I feel like it would be a waste of resources to select all the id's of each team and update them separately.

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  • Why is casting and comparing in PHP faster than is_*?

    - by tstenner
    While optimizing a function in PHP, I changed if(is_array($obj)) foreach($obj as $key=$value { [snip] } else if(is_object($obj)) foreach($obj as $key=$value { [snip] } to if($obj == (array) $obj) foreach($obj as $key=$value { [snip] } else if($obj == (obj) $obj) foreach($obj as $key=$value { [snip] } After learning about ===, I changed that to if($obj === (array) $obj) foreach($obj as $key=$value { [snip] } else if($obj === (obj) $obj) foreach($obj as $key=$value { [snip] } Changing each test from is_* to casting resulted in a major speedup (30%). I understand that === is faster than == as no coercion has to be done, but why is casting the variable so much faster than calling any of the is_*-functions?

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  • Why is i-- faster than i++ in loops? [closed]

    - by Afshin Mehrabani
    Possible Duplicate: JavaScript - Are loops really faster in reverse…? I don't know if this question is valid in other languages or not, but I'm asking this specifically for JavaScript. I see in some articles and questions that the fastest loop in JavaScript is something like: for(var i = array.length; i--; ) Also in Sublime Text 2, when you try to write a loop, it suggests: for (var i = Things.length - 1; i >= 0; i--) { Things[i] }; I want to know, why is i-- faster than i++ in loops?

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  • Help optimizing a query with 16 subqueries

    - by Webnet
    I have indexes/primaries on all appropriate ID fields for each type. I'm wondering though how I could make this more efficient. It takes a while to load the page with only 15,000 rows and that'll quickly grow to 500k. The $whereSql variable simply has a few more parameters for the main ebay_archive_listing table. NOTE: This is all done in a single query because I have ASC/DESC sorting for each subquery value. NOTE: I've converted some of the sub queries to INNER JOIN's SELECT product_master.product_id, ( SELECT COUNT(listing_id) FROM ebay_archive_product_listing_assoc '.$listingCountJoin.' WHERE ebay_archive_product_listing_assoc.product_id = product_master.product_id) as listing_count, sku, type_id, ( SELECT AVG(ebay_archive_listing.current_price) FROM ebay_archive_listing INNER JOIN ebay_archive_product_listing_assoc ON ( ebay_archive_product_listing_assoc.listing_id = ebay_archive_listing.id AND ebay_archive_product_listing_assoc.product_id = product_master.product_id ) WHERE '.$whereSql.' AND ebay_archive_listing.current_price > 0 ) as average_bid_price, ( SELECT AVG(ebay_archive_listing.buy_it_now_price) FROM ebay_archive_listing INNER JOIN ebay_archive_product_listing_assoc ON ( ebay_archive_product_listing_assoc.listing_id = ebay_archive_listing.id AND ebay_archive_product_listing_assoc.product_id = product_master.product_id ) WHERE '.$whereSql.' AND ebay_archive_listing.buy_it_now_price > 0 ) as average_buyout_price, ( SELECT MIN(ebay_archive_listing.current_price) FROM ebay_archive_listing INNER JOIN ebay_archive_product_listing_assoc ON ( ebay_archive_product_listing_assoc.listing_id = ebay_archive_listing.id AND ebay_archive_product_listing_assoc.product_id = product_master.product_id ) WHERE '.$whereSql.' AND ebay_archive_listing.current_price > 0 ) as lowest_bid_price, ( SELECT MAX(ebay_archive_listing.current_price) FROM ebay_archive_listing INNER JOIN ebay_archive_product_listing_assoc ON ( ebay_archive_product_listing_assoc.listing_id = ebay_archive_listing.id AND ebay_archive_product_listing_assoc.product_id = product_master.product_id ) WHERE '.$whereSql.' AND ebay_archive_listing.current_price > 0 ) as highest_bid_price, ( SELECT MIN(ebay_archive_listing.buy_it_now_price) FROM ebay_archive_listing INNER JOIN ebay_archive_product_listing_assoc ON ( ebay_archive_product_listing_assoc.listing_id = ebay_archive_listing.id AND ebay_archive_product_listing_assoc.product_id = product_master.product_id ) WHERE '.$whereSql.' AND ebay_archive_listing.current_price > 0 ) as lowest_buyout_price, ( SELECT MAX(ebay_archive_listing.buy_it_now_price) FROM ebay_archive_listing INNER JOIN ebay_archive_product_listing_assoc ON ( ebay_archive_product_listing_assoc.listing_id = ebay_archive_listing.id AND ebay_archive_product_listing_assoc.product_id = product_master.product_id ) WHERE '.$whereSql.' AND ebay_archive_listing.current_price > 0 ) as highest_buyout_price, round((( SELECT COUNT(ebay_archive_listing.id) FROM ebay_archive_listing INNER JOIN ebay_archive_product_listing_assoc ON ( ebay_archive_product_listing_assoc.listing_id = ebay_archive_listing.id AND ebay_archive_product_listing_assoc.product_id = product_master.product_id ) WHERE '.$whereSql.' AND ebay_archive_listing.status_id = 2 ) / ( SELECT COUNT(listing_id) FROM ebay_archive_product_listing_assoc '.$listingCountJoin.' WHERE ebay_archive_product_listing_assoc.product_id = product_master.product_id ) * 100), 1) as sold_percent FROM product_master '.$joinSql.' WHERE product_master.product_id IN ( SELECT product_id FROM ebay_archive_product_listing_assoc INNER JOIN ebay_archive_listing ON ( ebay_archive_listing.id = ebay_archive_product_listing_assoc.listing_id AND '.$whereSql.' ) )

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  • LOAD DATA LOCAL INFILE custom value

    - by NR03
    How to add a custom value using LOAD DATA LOCAL INFILE? The column time_added is the 7th column and the file has only 2 values for the first and the second column. For the 7th column, time_added I want to use the unix timestamp when loading from file. This code isn't working: $result = mysql_query("LOAD DATA LOCAL INFILE '{$myFile}' INTO TABLE {$table} FIELDS TERMINATED BY ':' LINES TERMINATED BY '\n' SET `time_added`=unix_timestamp()");

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  • PHP Try and Catch for SQL Insert

    - by meme
    I have a page on my website (high traffic) that does an insert on every page load. I am curious of the fastest and safest way to (catch an error) and continue if the system is not able to do the insert into MySQL. Should I use try/catch or die or something else. I want to make sure the insert happens but if for some reason it can't I want the page to continue to load anyway. ... $db = mysql_select_db('mobile', $conn); mysql_query("INSERT INTO redirects SET ua_string = '$ua_string'") or die('Error #10'); mysql_close($conn); ...

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  • SELECT * , COUNT( * ) FROM GROUP BY ORDER BY DESC

    - by quanganh_developer
    I have a table like: gold gold_city | gold_type | gold_selltime ------------------------------------- city1 | type 1 | 2012-01-01 city1 | type 1 | 2012-02-02 city1 | type 1 | 2012-03-03 city2 | type 2 | 2012-01-01 city2 | type 2 | 2012-02-02 city2 | type 2 | 2012-03-03 city3 | type 3 | 2012-01-01 city3 | type 3 | 2012-02-02 city3 | type 3 | 2012-03-03 How can I get 1 last result order by gold_selltime desc each group by gold_city and gold_type I used this: SELECT * , COUNT( * ) FROM gold_2012 GROUP BY gold_type , gold_city ORDER BY gold_selltime DESC but it did work. I only have result like: gold_city | gold_type | gold_selltime ------------------------------------- city1 | type 1 | 2012-01-01 city2 | type 2 | 2012-01-01 city3 | type 3 | 2012-01-01 but I need it like: gold_city | gold_type | gold_selltime ------------------------------------- city1 | type 1 | 2012-03-03 city2 | type 2 | 2012-03-03 city3 | type 3 | 2012-03-03

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  • Is it possible to put a form control on its own thread?

    - by BVernon
    I'm using a DataGridView and some operations that I do cause it to become unresponsive for periods of time. Normally I would put data processing in its own thread to make the form more responsive, but in this case it's the DataGridView itself that's taking so long. This leads me to wonder whether it's possible to have the main form on one thread and the DataGridView on another thread so it doesn't prevent the main form from responding. I completely understand that doing so is probably not 'safe' and likely opens up a can of worms that makes it hardly worth trying and I fully expect this post will be getting down votes for merely suggesting such a ridiculous idea. Is this possible? And if so how would you go about it?

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  • Android-SQLite: How to Count specific value from Column?

    - by sanpatil
    I have two table (TABLE_EXAM,TABLE_RESULT). Here is value of my TABLE_RESULT. result_id exam_id question_id correct_answer 1 2 4 y 2 2 5 y 3 2 6 n 4 2 7 y I need to count how many correct_answer='y' where exam_id=2. I try following code but it return 0. public int calculateResult(int examId,String confirmAnswer) { int correctAnswer=0; try { SQLiteDatabase db=this.getWritableDatabase(); String selectQuery=("select count(correctAnswer) from result where exam_id ='" + examId + "' and correctAnswer ='" + 'y' +"'" ); // String selectQuery=("SELECT COUNT(*)FROM result WHERE exam_id ='" + examId + "' and correctAnswer ='" + confirmAnswer +"'" ); Cursor cursor = db.rawQuery(selectQuery, null); if(cursor.moveToLast()) { correctAnswer=cursor.getInt(3); } } catch(Exception e) { e.printStackTrace(); } return correctAnswer; } In variable confirm_answer i pass "y". Give me some hint or reference. Any help is appreciated. Thanks in Advance

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