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  • Is it faster to count down than it is to count up?

    - by Bob
    Our computer science teacher once said that for some reason it is more efficient to count down that count up. For example if you need to use a FOR loop and the loop index is not used somewhere (like printing a line of N * to the screen) I mean that code like this : for (i=N; i>=0; i--) putchar('*'); is better than: for (i=0; i<N; i++) putchar('*'); Is it really true? and if so does anyone know why?

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  • Is it possible to make JQuery keydown respond faster?

    - by Drew Paul
    I am writing a simple page with JQuery and HTML5 canvas tags where I move a shape on the canvas by pressing 'w' for up, 's' for down, 'a' for left, and 'd' for right. I have it all working, but I would like the shape to start moving at a constant speed upon striking a key. Right now there is some kind of hold period and then the movement starts. How can I get the movement to occur immediately? Here the important part of my code: Your browser does not support the HTML5 canvas tag. start navigating coords should pop up here key should pop up here var c=document.getElementById("myCanvas"); var ctx=c.getContext("2d"); //keypress movements var xtriggered = 0; var keys = {}; var north = -10; var east = 10; var flipednorth = 0; $(document).ready(function(e){ $("input").keydown(function(){ keys[event.which] = true; if (event.which == 13) { event.preventDefault(); } //press w for north if (event.which == 87) { north++; flipednorth--; } //press s for south if (event.which == 83) { north--; flipednorth++; } //press d for east if (event.which == 68) { east++; } //press a for west if (event.which == 65) { east--; } var msg = 'x: ' + flipednorth*5 + ' y: ' + east*5; ctx.beginPath(); ctx.arc(east*6,flipednorth*6,40,0,2*Math.PI); ctx.stroke(); $('#soul2').html(msg); $('#soul3').html(event.which ); $("input").css("background-color","#FFFFCC"); }); $("input").keyup(function(){ delete keys[event.which]; $("input").css("background-color","#D6D6FF"); }); }); </script> please let me know if I shouldn't be posting code this lengthy.

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  • indexing for faster search of lists in a file??

    - by kaushik
    i have a file having around 1 lakh lists and have a another file with again a list of around an average of 50.. I want to compare 2nd item of list in second file with the 2nd element of 1st file and repeat this for each of the 50 lists in 2nd file and get the result of all the matching element. I have written the code for all this,but this is taking a lot of time as it need to check the whole the 1lakh list some 50 times..i want to improve the speed... please tell me how can i do this.... i cant not post my code as it is part of big code and will be difficult to infer anything from that... please tell what can be done to improve the speed?? thank u,

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  • How would I make this faster? Parsing Word/sorting by heading [on hold]

    - by Doof12
    Currently it takes about 3 minutes to run through a single 53 page word document. Hopefully you all have some advice about speeding up the process. Code: import win32com.client as win32 from glob import glob import io import re from collections import namedtuple from collections import defaultdict import pprint raw_files = glob('*.docx') word = win32.gencache.EnsureDispatch('Word.Application') word.Visible = False oFile = io.open("rawsort.txt", "w+", encoding = "utf-8")#text dump doccat= list() for f in raw_files: word.Documents.Open(f) doc = word.ActiveDocument #whichever document is active at the time doc.ConvertNumbersToText() print doc.Paragraphs.Count for x in xrange(1, doc.Paragraphs.Count+1):#for loop to print through paragraphs oText = doc.Paragraphs(x) if not oText.Range.Tables.Count >0 : results = re.match('(?P<number>(([1-3]*[A-D]*[0-9]*)(.[1-3]*[0-9])+))', oText.Range.Text) stylematch = re.match('Heading \d', oText.Style.NameLocal) if results!= None and oText.Style != None and stylematch != None: doccat.append((oText.Style.NameLocal, oText.Range.Text[:len(results.group('number'))],oText.Range.Text[len(results.group('number')):])) style = oText.Style.NameLocal else: if oText.Range.Font.Bold == True : doccat.append(style, oText) oFile.write(unicode(doccat)) oFile.close() The for Paragraph loop obviously takes the most amount of time. Is there some way of identifying and appending it without going through every Paragraph?

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  • Faster or more memory-efficient solution in Python for this Codejam problem.

    - by jeroen.vangoey
    I tried my hand at this Google Codejam Africa problem (the contest is already finished, I just did it to improve my programming skills). The Problem: You are hosting a party with G guests and notice that there is an odd number of guests! When planning the party you deliberately invited only couples and gave each couple a unique number C on their invitation. You would like to single out whoever came alone by asking all of the guests for their invitation numbers. The Input: The first line of input gives the number of cases, N. N test cases follow. For each test case there will be: One line containing the value G the number of guests. One line containing a space-separated list of G integers. Each integer C indicates the invitation code of a guest. Output For each test case, output one line containing "Case #x: " followed by the number C of the guest who is alone. The Limits: 1 = N = 50 0 < C = 2147483647 Small dataset 3 = G < 100 Large dataset 3 = G < 1000 Sample Input: 3 3 1 2147483647 2147483647 5 3 4 7 4 3 5 2 10 2 10 5 Sample Output: Case #1: 1 Case #2: 7 Case #3: 5 This is the solution that I came up with: with open('A-large-practice.in') as f: lines = f.readlines() with open('A-large-practice.out', 'w') as output: N = int(lines[0]) for testcase, i in enumerate(range(1,2*N,2)): G = int(lines[i]) for guest in range(G): codes = map(int, lines[i+1].split(' ')) alone = (c for c in codes if codes.count(c)==1) output.write("Case #%d: %d\n" % (testcase+1, alone.next())) It runs in 12 seconds on my machine with the large input. Now, my question is, can this solution be improved in Python to run in a shorter time or use less memory? The analysis of the problem gives some pointers on how to do this in Java and C++ but I can't translate those solutions back to Python.

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  • Is there a faster way to access a property member of a class using reflection?

    - by Ross Goddard
    I am currently using the following code to access the property of an object using reflection: Dim propInfo As Reflection.PropertyInfo = myType.GetProperty(propName) Dim objValue As Object = propInfo.GetValue(myObject, Nothing) I am having some issues with the speed since this type of code is being called many times and is causing some slowdown. I have been looking into using Refelction.Emit or dynamic methods, but I am not sure exactly how to make use of them. Background Information: I am creating a list of a subset of the properties of the object, associating then with some meta information (such as if they can be loaded from the database or xml, if they are editable, can the user see them). This is for later consumption so we can write code such as : foreach prop as BaseWrapper in graphNode.NodeProperties prop.LoadFromDataRow(dr) next The application makes heavy use of having access to this list. The problem is that on the initial load of a project, a larger number of objects are being created that make use of this, so for each object created it is looping through this code a number of times. I initially tried adding each property to the list manually, but this ran into problems with not everything being initialized at the correct time and some other issues. If there is no other good way, then I may have to rethink some of the design and see what else can be done to improve the performance.

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  • Faster way to convert from a String to generic type T when T is a valuetype?

    - by Kumba
    Does anyone know of a fast way in VB to go from a string to a generic type T constrained to a valuetype (Of T as Structure), when I know that T will always be some number type? This is too slow for my taste: Return DirectCast(Convert.ChangeType(myStr, GetType(T)), T) But it seems to be the only sane method of getting from a String -- T. I've tried using Reflector to see how Convert.ChangeType works, and while I can convert from the String to a given number type via a hacked-up version of that code, I have no idea how to jam that type back into T so it can be returned. I'll add that part of the speed penalty I'm seeing (in a timing loop) is because the return value is getting assigned to a Nullable(Of T) value. If I strongly-type my class for a specific number type (i.e., UInt16), then I can vastly increase the performance, but then the class would need to be duplicated for each numeric type that I use. It'd almost be nice if there was converter to/from T while working on it in a generic method/class. Maybe there is and I'm oblivious to its existence?

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  • Oracle Query Optimization: Why is My Second Query Faster?

    - by Patrick Cuff
    I was having some performance issues with an Oracle query, so I downloaded a trial of the Quest SQL Optimizer for Oracle, which made some changes that dramatically improved the query's performance. I'm not exactly sure why the recommended query had such an improvement; can anyone provide an explanation? Before: SELECT t1.version_id, t1.id, t2.field1, t3.person_id, t2.id FROM table1 t1, table2 t2, table3 t3 WHERE t1.id = t2.id AND t1.version_id = t2.version_id AND t2.id = 123 AND t1.version_id = t3.version_id AND t1.VERSION_NAME <> 'AA' order by t1.id Plan Cost: 831 Elapsed Time: 00:00:21.40 Number of Records: 40,717 After: SELECT /*+ USE_NL_WITH_INDEX(t1) */ t1.version_id, t1.id, t2.field1, t3.person_id, t2.id FROM table2 t2, table3 t3, table1 t1 WHERE t1.id = t2.id + 0 AND t1.version_id = t2.version_id + 0 AND t2.id = 123 AND t1.version_id = t3.version_id + 0 AND t1.VERSION_NAME || '' <> 'AA' AND t3.version_id = t2.version_id + 0 order by t1.id Plan Cost: 686 Elapsed Time: 00:00:00.95 Number of Records: 40,717 Questions: Why does re-arranging the order of the tables in the FROM clause help? Why does adding + 0 to the WHERE clause comparisons help? Why does || '' <> 'AA' in the WHERE clause VERSION_NAME comparison help? Is this a more efficient way of handling possible nulls on this column?

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  • c++ Sorting a vector based on values of other vector, or what's faster?

    - by pollux
    Hi, There are a couple of other posts about sorting a vector A based on values in another vector B. Most of the other answers tell to create a struct or a class to combine the values into one object and use std::sort. Though I'm curious about the performance of such solutions as I need to optimize code which implements bubble sort to sort these two vectors. I'm thinking to use a vector<pair<int,int>> and sort that. I'm working on a blob-tracking application (image analysis) where I try to match previously tracked blobs against newly detected blobs in video frames where I check each of the frames against a couple of previously tracked frames and of course the blobs I found in previous frames. I'm doing this at 60 times per second (speed of my webcam). Any advice on optimizing this is appreciated. The code I'm trying to optimize can be shown here: http://code.google.com/p/projectknave/source/browse/trunk/knaveAddons/ofxBlobTracker/ofCvBlobTracker.cpp?spec=svn313&r=313 Thanks

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  • Why is UDP + a software reliable ordering system faster than TCP?

    - by Ricket
    Some games today use a network system that transmits messages over UDP, and ensures that the messages are reliable and ordered. For example, RakNet is a popular game network engine. It uses only UDP for its connections, and has a whole system to ensure that packets can be reliable and ordered if you so choose. My basic question is, what's up with that? Isn't TCP the same thing as ordered, reliable UDP? What makes it so much slower that people have to basically reinvent the wheel?

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  • app engine's back referencing is too slow. How can I make it faster?

    - by Ray Yun
    Google app engine has smart feature named back references and I usually iterate them where the traditional SQL's computed column need to be used. Just imagine that need to accumulate specific force's total hp. class Force(db.Model): hp = db.IntegerProperty() class UnitGroup(db.Model): force = db.ReferenceProperty(reference_class=Force,collection_name="groups") hp = db.IntegerProperty() class Unit(db.Model): group = db.ReferenceProperty(reference_class=UnitGroup,collection_name="units") hp = db.IntegerProperty() When I code like following, it was horribly slow (almost 3s) with 20 forces with single group - single unit. (I guess back-referencing force reload sub entities. Am I right?) def get_hp(self): hp = 0 for group in self.groups: group_hp = 0 for unit in group.units: group_hp += unit.hp hp += group_hp return hp How can I optimize this code? Please consider that there are more properties should be computed for each force/unit-groups and I don't want to save these collective properties to each entities. :)

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  • Json, Timer, Ajax, What is faster (for shared cronometer) ?

    - by Felipe
    Hi everybody, I'm developing an application using ASP.Net. For first the idea: "My WebApp needs an cronometer to be shared by users and all users will se the same value in cronometer. When a user clicks on a button, the cronometer needs to be restarted and all users will need to see that!" All right, now I'd like to know what's the best choose to improve more performace an make sure that all users will see the same value in cronometer ? Need I use JSon (with jquery in client side), Timer with UpdatePanel of Ajax Extensions, pure Ajax (with JQuery) or any idea to suggested ? Any suggestion for how to shared a cronometer for all users in C# (put information in Cache or database) ? Thanks all Cheers

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  • memcached: which is faster, doing an add (and checking result), or doing a get (and set when returni

    - by Mike Sherov
    The title of this question isn't so clear, but the code and question is straightforward. Let's say I want to show my users an ad once per day. To accomplish this, every time they visit a page on my site, I check to see if a certain memcache key has any data stored on it. If so, don't show an ad. If not, store the value '1' in that key with an expiration of 86400. I can do this 2 ways: //version a $key='OPD_'.date('Ymd').'_'.$type.'_'.$user; if($memcache->get($key)===false){ $memcache->set($key,'1',false,$expire); //show ad } //version b $key='OPD_'.date('Ymd').'_'.$type.'_'.$user; if($memcache->add($key,'1',false,$expire)){ //show ad } Now, it might seem obvious that b is better, it always makes 1 memcache call. However, what is the overhead of "add" vs. "get"? These aren't the real comparisons... and I just made up these numbers, but let's say 1 add ~= 1 set ~= 5 get in terms of effort, and the average user views 5 pages a day: a: (5 get * 1 effort) + (1 set * 5 effort) = 10 units of effort b: (5 add * 5 effort) = 25 units of effort Would it make sense to always do the add call? Is this an unnecessary micro-optimization?

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  • Using Predicate of a class to Search Generic list - Faster than looping?

    - by Srikanth
    Lets say we have a generic list of Class1, typically having ~100 objects for a given session. I would like to see if the list has a particular object. ASP.NET 2.0 allows me to do this: Dim objResult as Class1 = objList.Find(objSearch) How does this approach rate when compared to a traditional For loop, looking at a performance perspective? How would this vary with increase or decrease in length of the list?

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  • What can we do to make XML processing faster?

    - by adpd
    We work on an internal corporate system that has a web front-end as one of its interfaces. The front-end (Java + Tomcat + Apache) communicates to the back-end (proprietary system written in a COBOL-like language) through SOAP web services. As a result, we pass large XML files back and forth. We believe that this architecture has a significant impact on performance due to the large overhead of XML transportation and parsing. Unfortunately, we are stuck with this architecture. How can we make this XML set-up more efficient? Any tips or techniques are greatly appreciated.

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  • How does java.util.Collections.contains() perform faster than a linear search?

    - by The111
    I've been fooling around with a bunch of different ways of searching collections, collections of collections, etc. Doing lots of stupid little tests to verify my understanding. Here is one which boggles me (source code further below). In short, I am generating N random integers and adding them to a list. The list is NOT sorted. I then use Collections.contains() to look for a value in the list. I intentionally look for a value that I know won't be there, because I want to ensure that the entire list space is probed. I time this search. I then do another linear search manually, iterating through each element of the list and checking if it matches my target. I also time this search. On average, the second search takes 33% longer than the first one. By my logic, the first search must also be linear, because the list is unsorted. The only possibility I could think of (which I immediately discard) is that Java is making a sorted copy of my list just for the search, but (1) I did not authorize that usage of memory space and (2) I would think that would result in MUCH more significant time savings with such a large N. So if both searches are linear, they should both take the same amount of time. Somehow the Collections class has optimized this search, but I can't figure out how. So... what am I missing? import java.util.*; public class ListSearch { public static void main(String[] args) { int N = 10000000; // number of ints to add to the list int high = 100; // upper limit for random int generation List<Integer> ints; int target = -1; // target will not be found, forces search of entire list space long start; long end; ints = new ArrayList<Integer>(); start = System.currentTimeMillis(); System.out.print("Generating new list... "); for (int i = 0; i < N; i++) { ints.add(((int) (Math.random() * high)) + 1); } end = System.currentTimeMillis(); System.out.println("took " + (end-start) + "ms."); start = System.currentTimeMillis(); System.out.print("Searching list for target (method 1)... "); if (ints.contains(target)) { // nothing } end = System.currentTimeMillis(); System.out.println(" Took " + (end-start) + "ms."); System.out.println(); ints = new ArrayList<Integer>(); start = System.currentTimeMillis(); System.out.print("Generating new list... "); for (int i = 0; i < N; i++) { ints.add(((int) (Math.random() * high)) + 1); } end = System.currentTimeMillis(); System.out.println("took " + (end-start) + "ms."); start = System.currentTimeMillis(); System.out.print("Searching list for target (method 2)... "); for (Integer i : ints) { // nothing } end = System.currentTimeMillis(); System.out.println(" Took " + (end-start) + "ms."); } }

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  • Is it faster to compute values in a query, call a Scalar Function (decimal(28,2) datatype) 4 times,

    - by Pulsehead
    I have a handful of queries I need to write in SQL Server 2005. Each Query will be calculating 4 unit cost values based on a handful of (up to 11) fields. Any time I want 1 of these 4 unit cost values, I'll want all 4. Which is quicker? Computing in the SQL Query ((a+b+c+d+e+f+g+h+i)/(j+k)), calling ComputeScalarUnitCost(datapoint.ID) 4 times, or joining to ComputeUnitCostTable(datapoint.ID) one time?

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  • MySQL VIEW vs. embedded query, which one is faster?

    - by Vincenzo
    I'm going to optimize a MySQL embedded query with a view, but I'm not sure whether it will give an effect: SELECT id FROM (SELECT * FROM t); I want to convert it to: CREATE VIEW v AS SELECT * FROM t; SELECT id FROM v; I've heard about "indexed views" in SQL Server, but I'm not sure about MySQL. Any help would be appreciated. Thanks!

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