Search Results

Search found 1071 results on 43 pages for 'integers'.

Page 40/43 | < Previous Page | 36 37 38 39 40 41 42 43  | Next Page >

  • Are there any working implementations of the rolling hash function used in the Rabin-Karp string sea

    - by c14ppy
    I'm looking to use a rolling hash function so I can take hashes of n-grams of a very large string. For example: "stackoverflow", broken up into 5 grams would be: "stack", "tacko", "ackov", "ckove", "kover", "overf", "verfl", "erflo", "rflow" This is ideal for a rolling hash function because after I calculate the first n-gram hash, the following ones are relatively cheap to calculate because I simply have to drop the first letter of the first hash and add the new last letter of the second hash. I know that in general this hash function is generated as: H = c1ak - 1 + c2ak - 2 + c3ak - 3 + ... + cka0 where a is a constant and c1,...,ck are the input characters. If you follow this link on the Rabin-Karp string search algorithm , it states that "a" is usually some large prime. I want my hashes to be stored in 32 bit integers, so how large of a prime should "a" be, such that I don't overflow my integer? Does there exist an existing implementation of this hash function somewhere that I could already use? Here is an implementation I created: public class hash2 { public int prime = 101; public int hash(String text) { int hash = 0; for(int i = 0; i < text.length(); i++) { char c = text.charAt(i); hash += c * (int) (Math.pow(prime, text.length() - 1 - i)); } return hash; } public int rollHash(int previousHash, String previousText, String currentText) { char firstChar = previousText.charAt(0); char lastChar = currentText.charAt(currentText.length() - 1); int firstCharHash = firstChar * (int) (Math.pow(prime, previousText.length() - 1)); int hash = (previousHash - firstCharHash) * prime + lastChar; return hash; } public static void main(String[] args) { hash2 hashify = new hash2(); int firstHash = hashify.hash("mydog"); System.out.println(firstHash); System.out.println(hashify.hash("ydogr")); System.out.println(hashify.rollHash(firstHash, "mydog", "ydogr")); } } I'm using 101 as my prime. Does it matter if my hashes will overflow? I think this is desirable but I'm not sure. Does this seem like the right way to go about this?

    Read the article

  • spoj: runlength

    - by user285825
    For RLM problem of SPOJ: This is the problem: "Run-length encoding of a number replaces a run of digits (that is, a sequence of consecutive equivalent digits) with the number of digits followed by the digit itself. For example, 44455 would become 3425 (three fours, two fives). Note that run-length encoding does not necessarily shorten the length of the data: 11 becomes 21, and 42 becomes 1412. If a number has more than nine consecutive digits of the same type, the encoding is done greedily: each run grabs as many digits as it can, so 111111111111111 is encoded as 9161. Implement an integer arithmetic calculator that takes operands and gives results in run-length format. You should support addition, subtraction, multiplication, and division. You won't have to divide by zero or deal with negative numbers. Input/Output The input will consist of several test cases, one per line. For each test case, compute the run-length mathematics expression and output the original expression and the result, as shown in the examples. The (decimal) representation of all operands and results will fit in signed 64-bit integers." These are my testcases: input: 11 + 11 988726 - 978625 12 * 41 1124 / 1112 13 * 33 15 / 16 19222317121013161815142715181017 + 10 10 + 19222317121013161815142715181017 19222317121013161815142715181017 / 19222317121013161815142715181017 19222317121013161815142715181017 / 11 11 / 19222317121013161815142715181017 19222317121013161815142715181017 / 12 12 / 19222317121013161815142715181017 19222317121013161815142715181017 / 141621161816101118141217131817191014 141621161816101118141217131817191014 / 19222317121013161815142715181017 19222317121013161815142715181017 / 141621161816101118141217131817191013 141621161816101118141217131817191013 / 19222317121013161815142715181017 19222317121013161815142715181017 * 11 11 * 19222317121013161815142715181017 19222317121013161815142715181017 * 10 10 * 19222317121013161815142715181017 19222317121013161815142715181017 - 10 19222317121013161815142715181017 - 19222317121013161815142715181017 19222317121013161815142715181017 - 141621161816101118141217131817191014 19222317121013161815142715181017 - 141621161816101118141217131817191013 141621161816101118141217131817191013 + 141621161816101118141217131817191013 141621161816101118141217131817191013 + 141621161816101118141217131817191014 141621161816101118141217131817191014 + 141621161816101118141217131817191013 141621161816101118141217131817191014 + 10 10 + 141621161816101118141217131817191013 141621161816101118141217131817191013 + 11 11 + 141621161816101118141217131817191013 141621161816101118141217131817191013 * 12 12 * 141621161816101118141217131817191013 141621161816101118141217131817191014 - 141621161816101118141217131817191014 141621161816101118141217131817191013 - 141621161816101118141217131817191013 141621161816101118141217131817191013 - 10 141621161816101118141217131817191014 - 11 141621161816101118141217131817191014 - 141621161816101118141217131817191013 141621161816101118141217131817191014 / 141621161816101118141217131817191014 141621161816101118141217131817191014 / 141621161816101118141217131817191013 141621161816101118141217131817191013 / 141621161816101118141217131817191014 141621161816101118141217131817191013 / 141621161816101118141217131817191013 141621161816101118141217131817191014 * 11 11 * 141621161816101118141217131817191014 141621161816101118141217131817191014 / 11 11 / 141621161816101118141217131817191014 10 + 10 10 + 11 10 + 15 15 + 10 11 + 10 11 + 10 10 - 10 15 - 10 10 * 10 10 * 15 15 * 10 10 / 111213 output: 11 + 11 = 12 988726 - 978625 = 919111 12 * 41 = 42 1124 / 1112 = 1112 13 * 33 = 39 15 / 16 = 10 19222317121013161815142715181017 + 10 = 19222317121013161815142715181017 10 + 19222317121013161815142715181017 = 19222317121013161815142715181017 19222317121013161815142715181017 / 19222317121013161815142715181017 = 11 19222317121013161815142715181017 / 11 = 19222317121013161815142715181017 11 / 19222317121013161815142715181017 = 10 19222317121013161815142715181017 / 12 = 141621161816101118141217131817191013 12 / 19222317121013161815142715181017 = 10 19222317121013161815142715181017 / 141621161816101118141217131817191014 = 11 141621161816101118141217131817191014 / 19222317121013161815142715181017 = 10 19222317121013161815142715181017 / 141621161816101118141217131817191013 = 12 141621161816101118141217131817191013 / 19222317121013161815142715181017 = 10 19222317121013161815142715181017 * 11 = 19222317121013161815142715181017 11 * 19222317121013161815142715181017 = 19222317121013161815142715181017 19222317121013161815142715181017 * 10 = 10 10 * 19222317121013161815142715181017 = 10 19222317121013161815142715181017 - 10 = 19222317121013161815142715181017 19222317121013161815142715181017 - 19222317121013161815142715181017 = 10 19222317121013161815142715181017 - 141621161816101118141217131817191014 = 141621161816101118141217131817191013 19222317121013161815142715181017 - 141621161816101118141217131817191013 = 141621161816101118141217131817191014 141621161816101118141217131817191013 + 141621161816101118141217131817191013 = 19222317121013161815142715181016 141621161816101118141217131817191013 + 141621161816101118141217131817191014 = 19222317121013161815142715181017 141621161816101118141217131817191014 + 141621161816101118141217131817191013 = 19222317121013161815142715181017 141621161816101118141217131817191014 + 10 = 141621161816101118141217131817191014 10 + 141621161816101118141217131817191013 = 141621161816101118141217131817191013 141621161816101118141217131817191013 + 11 = 141621161816101118141217131817191014 11 + 141621161816101118141217131817191013 = 141621161816101118141217131817191014 141621161816101118141217131817191013 * 12 = 19222317121013161815142715181016 12 * 141621161816101118141217131817191013 = 19222317121013161815142715181016 141621161816101118141217131817191014 - 141621161816101118141217131817191014 = 10 141621161816101118141217131817191013 - 141621161816101118141217131817191013 = 10 141621161816101118141217131817191013 - 10 = 141621161816101118141217131817191013 141621161816101118141217131817191014 - 11 = 141621161816101118141217131817191013 141621161816101118141217131817191014 - 141621161816101118141217131817191013 = 11 141621161816101118141217131817191014 / 141621161816101118141217131817191014 = 11 141621161816101118141217131817191014 / 141621161816101118141217131817191013 = 11 141621161816101118141217131817191013 / 141621161816101118141217131817191014 = 10 141621161816101118141217131817191013 / 141621161816101118141217131817191013 = 11 141621161816101118141217131817191014 * 11 = 141621161816101118141217131817191014 11 * 141621161816101118141217131817191014 = 141621161816101118141217131817191014 141621161816101118141217131817191014 / 11 = 141621161816101118141217131817191014 11 / 141621161816101118141217131817191014 = 10 10 + 10 = 10 10 + 11 = 11 10 + 15 = 15 15 + 10 = 15 11 + 10 = 11 11 + 10 = 11 10 - 10 = 10 15 - 10 = 15 10 * 10 = 10 10 * 15 = 10 15 * 10 = 10 10 / 111213 = 10 I am getting consistently wrong answer. I generated the above testcases trying to make them as representative as possible (boundary conditions, etc). I am not sure how to test it further. Some guidline would be really appreciated.

    Read the article

  • Diophantine Equation [closed]

    - by ANIL
    In mathematics, a Diophantine equation (named for Diophantus of Alexandria, a third century Greek mathematician) is a polynomial equation where the variables can only take on integer values. Although you may not realize it, you have seen Diophantine equations before: one of the most famous Diophantine equations is: X^n+Y^n=Z^n We are not certain that McDonald's knows about Diophantine equations (actually we doubt that they do), but they use them! McDonald's sells Chicken McNuggets in packages of 6, 9 or 20 McNuggets. Thus, it is possible, for example, to buy exactly 15 McNuggets (with one package of 6 and a second package of 9), but it is not possible to buy exactly 16 nuggets, since no non- negative integer combination of 6's, 9's and 20's adds up to 16. To determine if it is possible to buy exactly n McNuggets, one has to solve a Diophantine equation: find non-negative integer values of a, b, and c, such that 6a + 9b + 20c = n. Problem 1 Show that it is possible to buy exactly 50, 51, 52, 53, 54, and 55 McNuggets, by finding solutions to the Diophantine equation. You can solve this in your head, using paper and pencil, or writing a program. However you chose to solve this problem, list the combinations of 6, 9 and 20 packs of McNuggets you need to buy in order to get each of the exact amounts. Given that it is possible to buy sets of 50, 51, 52, 53, 54 or 55 McNuggets by combinations of 6, 9 and 20 packs, show that it is possible to buy 56, 57,..., 65 McNuggets. In other words, show how, given solutions for 50-55, one can derive solutions for 56-65. Problem 2 Write an iterative program that finds the largest number of McNuggets that cannot be bought in exact quantity. Your program should print the answer in the following format (where the correct number is provided in place of n): "Largest number of McNuggets that cannot be bought in exact quantity: n" Hints: Hypothesize possible instances of numbers of McNuggets that cannot be purchased exactly, starting with 1 For each possible instance, called n, a. Test if there exists non-negative integers a, b, and c, such that 6a+9b+20c = n. (This can be done by looking at all feasible combinations of a, b, and c) b. If not, n cannot be bought in exact quantity, save n When you have found six consecutive values of n that in fact pass the test of having an exact solution, the last answer that was saved (not the last value of n that had a solution) is the correct answer, since you know by the theorem that any amount larger can also be bought in exact quantity

    Read the article

  • Java ExecutorService java heap space ptoblems

    - by Sergey Aganezov jr
    I have a little bit of a problem in a multitasking java department. I have a class, called public class ThreadWorker implements Runnable { //some code in here public void run(){ // invokes some recursion method in the ThreadWorker itself, // which will stop eventually { } all in all, pretty simple "worker" that can work on it's on. To work with threads I'm using public static int THREAD_NUMBER = 4; public static ExecutorServide es = Executors.newFixedThreadPool(THREAD_NUMBER); adding instances of ThreadWroker class happens here: public void recursiveMethod(Arraylist<Integers> elements, MyClass data){ if (elements.size() == 0 && data.qualifies()){ ThreadWorker tw = new ThreadWorker(data); es.execute(tw); return; } for (int i=0; i< elements.size(); i++){ // some code to prevent my problem MyClass data1 = new MyClass(data); MyClass data2 = new MyClass(data); ArrayList<Integer> newElements = (ArrayList<Integer>)elements.clone(); data1.update(elements.get(i)); data2.update(-1 * elements.get(i)); newElements.remove(i); recursiveMethod(newElements, data1); recursiveMethod(newElements, data2); { } and the problem is that the depth of the recursion tree is quite big, so as it's width, so a lot of ThreadWorkers are added to the ExecutorService, so after some time on the big input a get Exception in thread "pool-1-thread-2" java.lang.OutOfMemoryError: Java heap space which is caused, as I think because of a ginormous number of ThreadWorkers i'm adding to ExecutorSirvice to be executed, so it runs out of memory. Every ThreadWorker takes about 40 Mb of RAM for all it needs. Is there a method to get how many threads (instances of classes implementing runnable interface) have been added to ExecutorService? So I can add it in the shown above code (int the " // some code to prevent my problem"), as while ("number of threads in the ExecutorService" > 10){ Thread.sleep(10000); } so I won't go to deep or to broad with my recursion and prevent those exception-throwing situations. Sincerely, Sergey Aganezov jr.

    Read the article

  • Advanced Django query with subselects and custom JOINS

    - by Bryan Ward
    I have been investigating this number theoretic function (found in the Height model) and I need to query for things based on the prime factorization of the primary key, or id. I have created a model for Factors of the id which maintains all of the prime factors. class Height(models.Model): b = models.IntegerField(null=True, blank=True) c = models.IntegerField(null=True, blank=True) d = models.FloatField(null=True, blank=True) class Factors(models.Model): height = models.ForeignKey(Height, null=True, blank=True) factor = models.IntegerField(null=True, blank=True) degree = models.IntegerField(null=True, blank=True) prime_id = models.IntegerField(null=True, blank=True) For example, if id=24, then the associated entries in the factors table would be height_id=24,factor=2,degree=3,prime_id=0 height_id=24,factor=3,degree=1,prime_id=1 the prime_id keep track of the relative order of the primes. Now let p < q < r < s all be prime numbers and a,b,c,d be positive integers. Then I want to be able to query for all Heights of the form id=(p**a)*(q**b)*(r**c)*(s**d). Now this is simple in the case that all of p,q,r,s,a,b,c,d are known in that I can just run Height.objects.get(id=(p**a)*(q**b)*(r**c)*(s**d)) But I need to be able to query for something like (2**a)*(3**2)*(r**c)*(s**d) where r,s,a,d are unknown and all Heights of such form will be returned. Furthermore, not all of the rows in Height will have exactly four prime factors, so I need to make sure that I am not matching rows of the form id=(p**a)*(q**b)*(r**c)*(s**d)*(t**e)... From what I can tell, the following MySQL query accomplishes this, but I would like to do it through the Django ORM. I also don't know if this MySQL query is the proper way to go about doing things. SELECT h.*,count(f.height_id) AS factorsCount FROM height AS h LEFT JOIN factors AS f ON ( f.height_id = h.id AND f.height_id IN (SELECT height_id FROM factors where prime_id=1 AND factor=2 AND degree=1) AND f.height_id IN (SELECT height_id FROM factors where prime_id=2 AND factor=3 AND degree=2) AND f.height_id IN (SELECT height_id FROM factors where prime_id=3 AND factor=5 AND degree=1) AND f.height_id IN (SELECT height_id FROM factors where prime_id=4 AND factor=7 ANd degree=1) ) GROUP BY h.id HAVING factorsCount=4 ORDER BY h.id; Any ideas or suggestions for things to try?

    Read the article

  • Perl Moose::Util::TypeConstraints bug ? what is this error about the name has invalid chars ?

    - by alex8657
    That has been hours i am tracking a Moose::Util::TypeConstraints exceptions, i don't understand where it gets to check a type and tells me that the name is incorrect. I tracked the error to a reduced example to try to locate the problem, and it just shows me that i do not get it. Did i get to a Moose::Util::TypeConstraints bug ? aoffice:new alex$ perl -c ../codesnippets/typeconstrainterror.pl ../codesnippets/typeconstrainterror.pl syntax OK aoffice:new alex$ perl -d ../codesnippets/typeconstrainterror.pl (...) DB<1> r Something::File::LocalFile=HASH(0x100d1bfa8) contains invalid characters for a type name. Names can contain alphanumeric character, ":", and "." at /opt/local/lib/perl5/vendor_perl/5.10.1/darwin-multi-2level/Moose/Util/TypeConstraints.pm line 508 Moose::Util::TypeConstraints::_create_type_constraint('Something::File::LocalFile=HASH(0x100d1bfa8)', undef, undef, undef, undef) called at /opt/local/lib/perl5/vendor_perl/5.10.1/darwin-multi-2level/Moose/Util/TypeConstraints.pm line 285 Moose::Util::TypeConstraints::type('Something::File::LocalFile=HASH(0x100d1bfa8)') called at ../codesnippets/typeconstrainterror.pl line 7 Something::File::is_slink('Something::File::LocalFile=HASH(0x100d1bfa8)') called at ../codesnippets/typeconstrainterror.pl line 33 Debugged program terminated. Use q to quit or R to restart, use o inhibit_exit to avoid stopping after program termination, h q, h R or h o to get additional info. Below, the code that crashes: package Something::File; use Moose; has 'type' =>(is=>'ro', isa=>'Str', writer=>'_set_type' ); sub is_slink { my $self = shift; return ( $self->type eq 'slink' ); } no Moose; __PACKAGE__->meta->make_immutable; 1; package Something::File::LocalFile; use Moose; use Moose::Util::TypeConstraints; extends 'Something::File'; subtype 'PositiveInt' => as 'Int' => where { $_ >0 } => message { 'Only positive greater than zero integers accepted' }; no Moose; __PACKAGE__->meta->make_immutable; 1; my $a = Something::File::LocalFile->new; # $a->_set_type('slink'); print $a->is_slink ." end\n";

    Read the article

  • Learning Treetop

    - by cmartin
    I'm trying to teach myself Ruby's Treetop grammar generator. I am finding that not only is the documentation woefully sparse for the "best" one out there, but that it doesn't seem to work as intuitively as I'd hoped. On a high level, I'd really love a better tutorial than the on-site docs or the video, if there is one. On a lower level, here's a grammar I cannot get to work at all: grammar SimpleTest rule num (float / integer) end rule float ( (( '+' / '-')? plain_digits '.' plain_digits) / (( '+' / '-')? plain_digits ('E' / 'e') plain_digits ) / (( '+' / '-')? plain_digits '.') / (( '+' / '-')? '.' plain_digits) ) { def eval text_value.to_f end } end rule integer (( '+' / '-' )? plain_digits) { def eval text_value.to_i end } end rule plain_digits [0-9] [0-9]* end end When I load it and run some assertions in a very simple test object, I find: assert_equal @parser.parse('3.14').eval,3.14 Works fine, while assert_equal @parser.parse('3').eval,3 raises the error: NoMethodError: private method `eval' called for # If I reverse integer and float on the description, both integers and floats give me this error. I think this may be related to limited lookahead, but I cannot find any information in any of the docs to even cover the idea of evaluating in the "or" context A bit more info that may help. Here's pp information for both those parse() blocks. The float: SyntaxNode+Float4+Float0 offset=0, "3.14" (eval,plain_digits): SyntaxNode offset=0, "" SyntaxNode+PlainDigits0 offset=0, "3": SyntaxNode offset=0, "3" SyntaxNode offset=1, "" SyntaxNode offset=1, "." SyntaxNode+PlainDigits0 offset=2, "14": SyntaxNode offset=2, "1" SyntaxNode offset=3, "4": SyntaxNode offset=3, "4" The Integer... note that it seems to have been defined to follow the integer rule, but not caught the eval() method: SyntaxNode+Integer0 offset=0, "3" (plain_digits): SyntaxNode offset=0, "" SyntaxNode+PlainDigits0 offset=0, "3": SyntaxNode offset=0, "3" SyntaxNode offset=1, "" Update: I got my particular problem working, but I have no clue why: rule integer ( '+' / '-' )? plain_digits { def eval text_value.to_i end } end This makes no sense with the docs that are present, but just removing the extra parentheses made the match include the Integer1 class as well as Integer0. Integer1 is apparently the class holding the eval() method. I have no idea why this is the case. I'm still looking for more info about treetop.

    Read the article

  • XQuery method question, trying to sum values read from xml

    - by Buck
    I'm pretty new to XQuery and I'm trying to write an example function that I can't get to work. I want to read an xml file, parse out the "time" values, sum them as they're read and return the sum. This is trivial and I'm looking to build more functionality into it but I'd like to get this working first. Also, I know there's a "sum" directive in XQuery that would do just this but I want to add more to it so the built-in sum is insufficient for my needs. Here's my funtion: bool example(Zorba* aZorba) { XQuery_t lQuery = aZorba-compileQuery( "for $i in fn:doc('/tmp/products.xml')//time" "let $sum := xs:integer($i)" " return $sum" ); DynamicContext* lCtx = lQuery-getDynamicContext(); lCtx-setContextItemAsDocument("temp_measurements.xml", lDocStream); try { std::cout << lQuery << std::endl; } catch (DynamicException& e) { std::cerr << e.getDescription() << std::endl; return false; } catch (StaticException& f){ std::cerr << f.getDescription() << f.getErrorCodeAsString(f.getErrorCode()) << std::endl; return false; } } It's called with an appropriate main(). If I comment out the line that starts "let $sum..." then this works in that it returns the time values as a series of integers like this: 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 3 3 3 3 3 3 3 3 3.... Input file looks like this: <?xml version="1.0" encoding="UTF-8"? <temps <temp <time0</time <lat0</lat <long0</long <value0</value </temp <temp <time1</time <lat0</lat <long1</long <value0</value </temp ...

    Read the article

  • Marshal.PtrToStructure (and back again) and generic solution for endianness swapping

    - by cgyDeveloper
    I have a system where a remote agent sends serialized structures (from and embedded C system) for me to read and store via IP/UDP. In some cases I need to send back the same structure types. I thought I had a nice setup using Marshal.PtrToStructure (receive) and Marshal.StructureToPtr (send). However, a small gotcha is that the network big endian integers need to be converted to my x86 little endian format to be used locally. When I'm sending them off again, big endian is the way to go. Here are the functions in question: private static T BytesToStruct<T>(ref byte[] rawData) where T: struct { T result = default(T); GCHandle handle = GCHandle.Alloc(rawData, GCHandleType.Pinned); try { IntPtr rawDataPtr = handle.AddrOfPinnedObject(); result = (T)Marshal.PtrToStructure(rawDataPtr, typeof(T)); } finally { handle.Free(); } return result; } private static byte[] StructToBytes<T>(T data) where T: struct { byte[] rawData = new byte[Marshal.SizeOf(data)]; GCHandle handle = GCHandle.Alloc(rawData, GCHandleType.Pinned); try { IntPtr rawDataPtr = handle.AddrOfPinnedObject(); Marshal.StructureToPtr(data, rawDataPtr, false); } finally { handle.Free(); } return rawData; } And a quick example structure that might be used like this: byte[] data = this.sock.Receive(ref this.ipep); Request request = BytesToStruct<Request>(ref data); Where the structure in question looks like: [StructLayout(LayoutKind.Sequential, CharSet = CharSet.Ansi, Pack = 1)] private struct Request { public byte type; public short sequence; [MarshalAs(UnmanagedType.ByValArray, SizeConst = 5)] public byte[] address; } What (generic) way can I swap the endianness when marshalling the structures? My need is such that the locally stored 'public short sequence' in this example will be little-endian for displaying to the user. I don't want to have to swap the endianness on a structure-specific way. My first thought was to use Reflection, but I'm not very familiar with that feature. Also, I hoped that there would be a better solution out there that somebody could point me towards. Thanks in advance :)

    Read the article

  • Rtti accessing fields and properties in complex data structures

    - by Coco
    As already discussed in Rtti data manipulation and consistency in Delphi 2010 a consistency between the original data and rtti values can be reached by accessing members by using a pair of TRttiField and an instance pointer. This would be very easy in case of a simple class with only basic member types (like e.g. integers or strings). But what if we have structured field types? Here is an example: TIntArray = array [0..1] of Integer; TPointArray = array [0..1] of Point; TExampleClass = class private FPoint : TPoint; FAnotherClass : TAnotherClass; FIntArray : TIntArray; FPointArray : TPointArray; public property Point : TPoint read FPoint write FPoint; //.... and so on end; For an easy access of Members I want to buil a tree of member-nodes, which provides an interface for getting and setting values, getting attributes, serializing/deserializing values and so on. TMemberNode = class private FMember : TRttiMember; FParent : TMemberNode; FInstance : Pointer; public property Value : TValue read GetValue write SetValue; //uses FInstance end; So the most important thing is getting/setting the values, which is done - as stated before - by using the GetValue and SetValue functions of TRttiField. So what is the Instance for FPoint members? Let's say Parent is the Node for TExample class, where the instance is known and the member is a field, then Instance would be: FInstance := Pointer (Integer (Parent.Instance) + TRttiField (FMember).Offset); But what if I want to know the Instance for a record property? There is no offset in this case. So is there a better solution to get a pointer to the data? For the FAnotherClass member, the Instance would be: FInstance := Parent.Value.AsObject; So far the solution works, and data manipulation can be done by using rtti or the original types, without losing information. But things get harder, when working with arrays. Especially the second array of Points. How can I get the instance for the members of points in this case?

    Read the article

  • Coming Up with a Good Algorithm for a Simple Idea

    - by mkoryak
    I need to come up with an algorithm that does the following: Lets say you have an array of positive numbers (e.g. [1,3,7,0,0,9]) and you know beforehand their sum is 20. You want to abstract some average amount from each number such that the new sum would be less by 7. To do so, you must follow these rules: you can only subtract integers the resulting array must not have any negative values you can not make any changes to the indices of the buckets. The more uniformly the subtraction is distributed over the array the better. Here is my attempt at an algorithm in JavaScript + underscore (which will probably make it n^2): function distributeSubtraction(array, goal){ var sum = _.reduce(arr, function(x, y) { return x + y; }, 0); if(goal < sum){ while(goal < sum && goal > 0){ var less = ~~(goal / _.filter(arr, _.identity).length); //length of array without 0s arr = _.map(arr, function(val){ if(less > 0){ return (less < val) ? val - less : val; //not ideal, im skipping some! } else { if(goal > 0){ //again not ideal. giving preference to start of array if(val > 0) { goal--; return val - 1; } } else { return val; } } }); if(goal > 0){ var newSum = _.reduce(arr, function(x, y) { return x + y; }, 0); goal -= sum - newSum; sum = newSum; } else { return arr; } } } else if(goal == sum) { return _.map(arr, function(){ return 0; }); } else { return arr; } } var goal = 7; var arr = [1,3,7,0,0,9]; var newArray = distributeSubtraction(arr, goal); //returned: [0, 1, 5, 0, 0, 7]; Well, that works but there must be a better way! I imagine the run time of this thing will be terrible with bigger arrays and bigger numbers. edit: I want to clarify that this question is purely academic. Think of it like an interview question where you whiteboard something and the interviewer asks you how your algorithm would behave on a different type of a dataset.

    Read the article

  • "Simple" sort a nested array using array_multisort or native PHP functions instead of my own foreach loop

    - by Ana Ban
    I have the following array of days of the week, with each day having hours of the day (the whole array represents the schedule of a part-time employee): Array ( [7] => Array ( [0] => 15 [1] => 14 [2] => 13 [3] => 11 [4] => 12 [5] => 10 ) [1] => Array ( [0] => 10 [1] => 13 [2] => 12 ) [6] => Array ( [0] => 14 ) [3] => Array ( [0] => 4 [1] => 5 [2] => 6 ) ) and I simply need to: sort asc each sub-array (2nd dimension) - no need to maintain the numeric keys, values are integers sort asc the 1st dimension and maintain the numeric, integer keys ie: Array ( [1] => Array ( [0] => 10 [1] => 12 [2] => 13 ) [3] => Array ( [0] => 4 [1] => 5 [2] => 6 ) [6] => Array ( [0] => 14 ) [7] => Array ( [0] => 10 [1] => 11 [2] => 12 [3] => 13 [4] => 14 [5] => 15 ) ) Additional info: only the keys of the 1st dimension and the values of the 2nd dimension (and of course their association) are meaningful to my use-case the 1st dimension can have at most 7 values, ranging from 1-7 (days of the week), and will have at least 1 value (1 day) the 2nd dimension can have at most 24 values, ranging from 0-23 (hours of each day), and will have at least 1 value (1 hour per day) I know I can do this with a foreach on the whole ksorted array and sort each 2nd dimension array: ksort($sched); foreach ($sched as &$array) sort($array); unset($array); but I was hoping I could achieve this with native php array function(s) instead. My search led me to try array_multisort(array_values($array), array_keys($array), $array) but I just can't make it work.

    Read the article

  • average velocity, as3

    - by VideoDnd
    Hello, I need something accurate I can plug equations in to if you can help. How would you apply the equation bellow? Thanks guys. AVERAGE VELOCITY AND DISPLACEMENT average velocity V=X/T displacement x=v*T more info example I have 30 seconds and a field that is 170 yards. What average velocity would I need my horse to travel at to reach the end of the field in 30 seconds. I moved the decimal places around and got this. Here's what I tried 'the return value is close, but not close enough' FLA here var TIMER:int = 10; var T:int = 0; var V:int = 5.6; var X:int = 0; var Xf:int = 17000/10*2; var timer:Timer = new Timer(TIMER,Xf); timer.addEventListener(TimerEvent.TIMER, incrementCounter); timer.start(); function formatCount(i:int):String { var fraction:int = Math.abs(i % 100); var whole:int = Math.abs(i / 100); return ("0000000" + whole).substr(-7, 7) + "." + (fraction < 10 ? "0" + fraction : fraction); } function incrementCounter(event:TimerEvent) { T++; X = Math.abs(V*T); text.text = formatCount(X); } tests TARGET 5.6yards * 30seconds = 168yards INTEGERS 135.00 in 30 seconds MATH.ROUND 135.00 in 30 seconds NUMBERS 140.00 in 30 seconds control timer 'I tested with this and the clock on my desk' var timetest:Timer = new Timer(1000,30); var Dplus:int = 17000; timetest.addEventListener(TimerEvent.TIMER, cow); timetest.start(); function cow(evt:TimerEvent):void { tx.text = String("30 SECONDS: " + timetest.currentCount); if(timetest.currentCount> Dplus){ timetest.stop(); } } //far as I got...couldn't get delta to work... T = (V*timer.currentCount); X += Math.round(T);

    Read the article

  • Exception opening TAdoDataset: Arguments are of the wrong type, are out of acceptable range, or are

    - by Dave Falkner
    I've been trying to debug the following problem for several weeks now - this method is called from several places within the same datamodule, but this exception (from the subject line of this post) only occurs when integers for a certain purpose (pickup orders vs. orders that we ship through a carrier) are used - and don't ask me how the application can tell the difference between one integer's purpose and another! Furthermore, I cannot duplicate this issue on my machine - the error occurs on a warehouse machine but not my own development machine, even when working with the same production database. I have suspected an MDAC version conflict between the two machines, but have run a version checker and confirmed that both machines are running 2.8, and additionally have confirmed this by logging the TAdoDataset's .Version property at runtime. function TdmESShip.SecondaryID(const PrimaryID : Integer ): String; begin try with qESPackage2 do begin if Active then Close; LogMessage('-----------------------------------'); LogMessage('Version: ' + FConnection.Version); LogMessage('DB Info: ' + FConnection.Properties['Initial Catalog'].Value + ' ' + FConnection.Properties['Data Source'].Value); LogMessage('Setting the parameter.'); Parameters.ParamByName('ParameterName').Value := PrimaryID; LogMessage('Done setting the parameter.'); Open; Ninety-nine times out of 100 this logging code logs a successful operation as follows: Version: 2.8 DB Info: (database name and instance) Setting the parameter. Done setting the parameter. Opened the dataset. But then whenever a "pickup" order is processed, this exception gets thrown whenever the dataset is opened: Version: 2.8 DB Info: (database name and instance) Setting the parameter. Done setting the parameter. GetESPackageID() threw an exception. Type: EOleException, Message: Arguments are of the wrong type, are out of acceptable range, or are in conflict with one another Error: Arguments are of the wrong type, are out of acceptable range, or are in conflict with one another for packageID 10813711 I've tried eliminating the parameter and have built the commandtext for this dataset programmatically, suspecting that some part of the TParameter's configuration might be out of whack, but the same error occurs under the same circumstances. I've tried every combination of TParameter properties that I can think of - this is the millionth TParameter I've created for my millionth dataset, and I've never encountered this error. I've even created a second dataset from scratch and removed all references to the original dataset in case some property of the original dataset in the .dfm might be corrupted, but the same error occurs under the same circumstances. The commandtext for this dataset is a simple select ValueA from TableName where ValueB = @ParameterB I'm about ready to do something extreme, such as writing a web service to look these values up - it feels right now as though I could destroy my machine, rebuild it, rewrite this entire application from scratch, and the application would still know to throw an exception whenever I try to look up a secondary value from a primary value, but only for pickup orders, and only from the one machine in the warehouse, but I'm probably missing something simple. So, any help anyone could provide would be greatly appreciated.

    Read the article

  • Opinion on "loop invariants", and are these frequently used in the industry?

    - by Michael Aaron Safyan
    I was thinking back to my freshman year at college (five years ago) when I took an exam to place-out of intro-level computer science. There was a question about loop invariants, and I was wondering if loop invariants are really necessary in this case or if the question was simply a bad example... the question was to write an iterative definition for a factorial function, and then to prove that the function was correct. The code that I provided for the factorial function was as follows: public static int factorial(int x) { if ( x < 0 ){ throw new IllegalArgumentException("Parameter must be = 0"); }else if ( x == 0 ){ return 1; }else{ int result = 1; for ( int i = 1; i <= x; i++ ){ result*=i; } return result; } } My own proof of correctness was a proof by cases, and in each I asserted that it was correct by definition (x! is undefined for negative values, 0! is 1, and x! is 1*2*3...*x for a positive value of x). The professor wanted me to prove the loop using a loop invariant; however, my argument was that it was correct "by definition", because the definition of "x!" for a positive integer x is "the product of the integers from 1... x", and the for-loop in the else clause is simply a literal translation of this definition. Is a loop invariant really needed as a proof of correctness in this case? How complicated must a loop be before a loop invariant (and proper initialization and termination conditions) become necessary for a proof of correctness? Additionally, I was wondering... how often are such formal proofs used in the industry? I have found that about half of my courses are very theoretical and proof-heavy and about half are very implementation and coding-heavy, without any formal or theoretical material. How much do these overlap in practice? If you do use proofs in the industry, when do you apply them (always, only if it's complicated, rarely, never)?

    Read the article

  • realloc - converting int to char

    - by Mike
    I'm converting an array of integers into a char by iterating through the whole array, and then I'm adding the resulting string to ncurses's method new_item. For some reason I'm doing something wrong the way I reallocate memory, thus I get the the first column as: -4 Choice 1 0 Choice 1 4 Choice 2 1 Choice 1 4 Choice 3 - Instead of - 2 Choice 1 4 Choice 4 3 Choice 1 4 Exit 4 Choice 1 - #include <stdio.h> #include <stdlib.h> #include <curses.h> #include <menu.h> #define ARRAY_SIZE(a) (sizeof(a) / sizeof(a[0])) #define CTRLD 4 char *choices[] = { "Choice 1", "Choice 2", "Choice 3", "Choice 4", "Exit", }; int table[5]={0,1,2,3,4}; int main() { ITEM **my_items; int c; MENU *my_menu; int n_choices, i; ITEM *cur_item; initscr(); cbreak(); noecho(); keypad(stdscr, TRUE); n_choices = ARRAY_SIZE(choices); my_items = (ITEM **)calloc(n_choices + 1, sizeof(ITEM *)); // right here char *convert = NULL; for(i = 0; i < n_choices; ++i){ convert = (char *) realloc (convert, sizeof(char) * 4); sprintf(convert, "%i", table[i]); my_items[i] = new_item(convert, choices[i]); } my_items[n_choices] = (ITEM *)NULL; my_menu = new_menu((ITEM **)my_items); mvprintw(LINES - 2, 0, "F1 to Exit"); post_menu(my_menu); refresh(); while((c = getch()) != KEY_F(1)) { switch(c) { case KEY_DOWN: menu_driver(my_menu, REQ_DOWN_ITEM); break; case KEY_UP: menu_driver(my_menu, REQ_UP_ITEM); break; } } free(convert); unpost_menu(my_menu); free_item(my_items[0]); free_item(my_items[1]); free_item(my_items[2]); free_item(my_items[3]); free_item(my_items[4]); free_menu(my_menu); endwin(); }

    Read the article

  • Steganography Experiment - Trouble hiding message bits in DCT coefficients

    - by JohnHankinson
    I have an application requiring me to be able to embed loss-less data into an image. As such I've been experimenting with steganography, specifically via modification of DCT coefficients as the method I select, apart from being loss-less must also be relatively resilient against format conversion, scaling/DSP etc. From the research I've done thus far this method seems to be the best candidate. I've seen a number of papers on the subject which all seem to neglect specific details (some neglect to mention modification of 0 coefficients, or modification of AC coefficient etc). After combining the findings and making a few modifications of my own which include: 1) Using a more quantized version of the DCT matrix to ensure we only modify coefficients that would still be present should the image be JPEG'ed further or processed (I'm using this in place of simply following a zig-zag pattern). 2) I'm modifying bit 4 instead of the LSB and then based on what the original bit value was adjusting the lower bits to minimize the difference. 3) I'm only modifying the blue channel as it should be the least visible. This process must modify the actual image and not the DCT values stored in file (like jsteg) as there is no guarantee the file will be a JPEG, it may also be opened and re-saved at a later stage in a different format. For added robustness I've included the message multiple times and use the bits that occur most often, I had considered using a QR code as the message data or simply applying the reed-solomon error correction, but for this simple application and given that the "message" in question is usually going to be between 10-32 bytes I have plenty of room to repeat it which should provide sufficient redundancy to recover the true bits. No matter what I do I don't seem to be able to recover the bits at the decode stage. I've tried including / excluding various checks (even if it degrades image quality for the time being). I've tried using fixed point vs. double arithmetic, moving the bit to encode, I suspect that the message bits are being lost during the IDCT back to image. Any thoughts or suggestions on how to get this working would be hugely appreciated. (PS I am aware that the actual DCT/IDCT could be optimized from it's naive On4 operation using row column algorithm, or an FDCT like AAN, but for now it just needs to work :) ) Reference Papers: http://www.lokminglui.com/dct.pdf http://arxiv.org/ftp/arxiv/papers/1006/1006.1186.pdf Code for the Encode/Decode process in C# below: using System; using System.Collections.Generic; using System.Linq; using System.Text; using System.Drawing.Imaging; using System.Drawing; namespace ImageKey { public class Encoder { public const int HIDE_BIT_POS = 3; // use bit position 4 (1 << 3). public const int HIDE_COUNT = 16; // Number of times to repeat the message to avoid error. // JPEG Standard Quantization Matrix. // (to get higher quality multiply by (100-quality)/50 .. // for lower than 50 multiply by 50/quality. Then round to integers and clip to ensure only positive integers. public static double[] Q = {16,11,10,16,24,40,51,61, 12,12,14,19,26,58,60,55, 14,13,16,24,40,57,69,56, 14,17,22,29,51,87,80,62, 18,22,37,56,68,109,103,77, 24,35,55,64,81,104,113,92, 49,64,78,87,103,121,120,101, 72,92,95,98,112,100,103,99}; // Maximum qauality quantization matrix (if all 1's doesn't modify coefficients at all). public static double[] Q2 = {1,1,1,1,1,1,1,1, 1,1,1,1,1,1,1,1, 1,1,1,1,1,1,1,1, 1,1,1,1,1,1,1,1, 1,1,1,1,1,1,1,1, 1,1,1,1,1,1,1,1, 1,1,1,1,1,1,1,1, 1,1,1,1,1,1,1,1}; public static Bitmap Encode(Bitmap b, string key) { Bitmap response = new Bitmap(b.Width, b.Height, PixelFormat.Format32bppArgb); uint imgWidth = ((uint)b.Width) & ~((uint)7); // Maximum usable X resolution (divisible by 8). uint imgHeight = ((uint)b.Height) & ~((uint)7); // Maximum usable Y resolution (divisible by 8). // Start be transferring the unmodified image portions. // As we'll be using slightly less width/height for the encoding process we'll need the edges to be populated. for (int y = 0; y < b.Height; y++) for (int x = 0; x < b.Width; x++) { if( (x >= imgWidth && x < b.Width) || (y>=imgHeight && y < b.Height)) response.SetPixel(x, y, b.GetPixel(x, y)); } // Setup the counters and byte data for the message to encode. StringBuilder sb = new StringBuilder(); for(int i=0;i<HIDE_COUNT;i++) sb.Append(key); byte[] codeBytes = System.Text.Encoding.ASCII.GetBytes(sb.ToString()); int bitofs = 0; // Current bit position we've encoded too. int totalBits = (codeBytes.Length * 8); // Total number of bits to encode. for (int y = 0; y < imgHeight; y += 8) { for (int x = 0; x < imgWidth; x += 8) { int[] redData = GetRedChannelData(b, x, y); int[] greenData = GetGreenChannelData(b, x, y); int[] blueData = GetBlueChannelData(b, x, y); int[] newRedData; int[] newGreenData; int[] newBlueData; if (bitofs < totalBits) { double[] redDCT = DCT(ref redData); double[] greenDCT = DCT(ref greenData); double[] blueDCT = DCT(ref blueData); int[] redDCTI = Quantize(ref redDCT, ref Q2); int[] greenDCTI = Quantize(ref greenDCT, ref Q2); int[] blueDCTI = Quantize(ref blueDCT, ref Q2); int[] blueDCTC = Quantize(ref blueDCT, ref Q); HideBits(ref blueDCTI, ref blueDCTC, ref bitofs, ref totalBits, ref codeBytes); double[] redDCT2 = DeQuantize(ref redDCTI, ref Q2); double[] greenDCT2 = DeQuantize(ref greenDCTI, ref Q2); double[] blueDCT2 = DeQuantize(ref blueDCTI, ref Q2); newRedData = IDCT(ref redDCT2); newGreenData = IDCT(ref greenDCT2); newBlueData = IDCT(ref blueDCT2); } else { newRedData = redData; newGreenData = greenData; newBlueData = blueData; } MapToRGBRange(ref newRedData); MapToRGBRange(ref newGreenData); MapToRGBRange(ref newBlueData); for(int dy=0;dy<8;dy++) { for(int dx=0;dx<8;dx++) { int col = (0xff<<24) + (newRedData[dx+(dy*8)]<<16) + (newGreenData[dx+(dy*8)]<<8) + (newBlueData[dx+(dy*8)]); response.SetPixel(x+dx,y+dy,Color.FromArgb(col)); } } } } if (bitofs < totalBits) throw new Exception("Failed to encode data - insufficient cover image coefficients"); return (response); } public static void HideBits(ref int[] DCTMatrix, ref int[] CMatrix, ref int bitofs, ref int totalBits, ref byte[] codeBytes) { int tempValue = 0; for (int u = 0; u < 8; u++) { for (int v = 0; v < 8; v++) { if ( (u != 0 || v != 0) && CMatrix[v+(u*8)] != 0 && DCTMatrix[v+(u*8)] != 0) { if (bitofs < totalBits) { tempValue = DCTMatrix[v + (u * 8)]; int bytePos = (bitofs) >> 3; int bitPos = (bitofs) % 8; byte mask = (byte)(1 << bitPos); byte value = (byte)((codeBytes[bytePos] & mask) >> bitPos); // 0 or 1. if (value == 0) { int a = DCTMatrix[v + (u * 8)] & (1 << HIDE_BIT_POS); if (a != 0) DCTMatrix[v + (u * 8)] |= (1 << HIDE_BIT_POS) - 1; DCTMatrix[v + (u * 8)] &= ~(1 << HIDE_BIT_POS); } else if (value == 1) { int a = DCTMatrix[v + (u * 8)] & (1 << HIDE_BIT_POS); if (a == 0) DCTMatrix[v + (u * 8)] &= ~((1 << HIDE_BIT_POS) - 1); DCTMatrix[v + (u * 8)] |= (1 << HIDE_BIT_POS); } if (DCTMatrix[v + (u * 8)] != 0) bitofs++; else DCTMatrix[v + (u * 8)] = tempValue; } } } } } public static void MapToRGBRange(ref int[] data) { for(int i=0;i<data.Length;i++) { data[i] += 128; if(data[i] < 0) data[i] = 0; else if(data[i] > 255) data[i] = 255; } } public static int[] GetRedChannelData(Bitmap b, int sx, int sy) { int[] data = new int[8 * 8]; for (int y = sy; y < (sy + 8); y++) { for (int x = sx; x < (sx + 8); x++) { uint col = (uint)b.GetPixel(x,y).ToArgb(); data[(x - sx) + ((y - sy) * 8)] = (int)((col >> 16) & 0xff) - 128; } } return (data); } public static int[] GetGreenChannelData(Bitmap b, int sx, int sy) { int[] data = new int[8 * 8]; for (int y = sy; y < (sy + 8); y++) { for (int x = sx; x < (sx + 8); x++) { uint col = (uint)b.GetPixel(x, y).ToArgb(); data[(x - sx) + ((y - sy) * 8)] = (int)((col >> 8) & 0xff) - 128; } } return (data); } public static int[] GetBlueChannelData(Bitmap b, int sx, int sy) { int[] data = new int[8 * 8]; for (int y = sy; y < (sy + 8); y++) { for (int x = sx; x < (sx + 8); x++) { uint col = (uint)b.GetPixel(x, y).ToArgb(); data[(x - sx) + ((y - sy) * 8)] = (int)((col >> 0) & 0xff) - 128; } } return (data); } public static int[] Quantize(ref double[] DCTMatrix, ref double[] Q) { int[] DCTMatrixOut = new int[8*8]; for (int u = 0; u < 8; u++) { for (int v = 0; v < 8; v++) { DCTMatrixOut[v + (u * 8)] = (int)Math.Round(DCTMatrix[v + (u * 8)] / Q[v + (u * 8)]); } } return(DCTMatrixOut); } public static double[] DeQuantize(ref int[] DCTMatrix, ref double[] Q) { double[] DCTMatrixOut = new double[8*8]; for (int u = 0; u < 8; u++) { for (int v = 0; v < 8; v++) { DCTMatrixOut[v + (u * 8)] = (double)DCTMatrix[v + (u * 8)] * Q[v + (u * 8)]; } } return(DCTMatrixOut); } public static double[] DCT(ref int[] data) { double[] DCTMatrix = new double[8 * 8]; for (int v = 0; v < 8; v++) { for (int u = 0; u < 8; u++) { double cu = 1; if (u == 0) cu = (1.0 / Math.Sqrt(2.0)); double cv = 1; if (v == 0) cv = (1.0 / Math.Sqrt(2.0)); double sum = 0.0; for (int y = 0; y < 8; y++) { for (int x = 0; x < 8; x++) { double s = data[x + (y * 8)]; double dctVal = Math.Cos((2 * y + 1) * v * Math.PI / 16) * Math.Cos((2 * x + 1) * u * Math.PI / 16); sum += s * dctVal; } } DCTMatrix[u + (v * 8)] = (0.25 * cu * cv * sum); } } return (DCTMatrix); } public static int[] IDCT(ref double[] DCTMatrix) { int[] Matrix = new int[8 * 8]; for (int y = 0; y < 8; y++) { for (int x = 0; x < 8; x++) { double sum = 0; for (int v = 0; v < 8; v++) { for (int u = 0; u < 8; u++) { double cu = 1; if (u == 0) cu = (1.0 / Math.Sqrt(2.0)); double cv = 1; if (v == 0) cv = (1.0 / Math.Sqrt(2.0)); double idctVal = (cu * cv) / 4.0 * Math.Cos((2 * y + 1) * v * Math.PI / 16) * Math.Cos((2 * x + 1) * u * Math.PI / 16); sum += (DCTMatrix[u + (v * 8)] * idctVal); } } Matrix[x + (y * 8)] = (int)Math.Round(sum); } } return (Matrix); } } public class Decoder { public static string Decode(Bitmap b, int expectedLength) { expectedLength *= Encoder.HIDE_COUNT; uint imgWidth = ((uint)b.Width) & ~((uint)7); // Maximum usable X resolution (divisible by 8). uint imgHeight = ((uint)b.Height) & ~((uint)7); // Maximum usable Y resolution (divisible by 8). // Setup the counters and byte data for the message to decode. byte[] codeBytes = new byte[expectedLength]; byte[] outBytes = new byte[expectedLength / Encoder.HIDE_COUNT]; int bitofs = 0; // Current bit position we've decoded too. int totalBits = (codeBytes.Length * 8); // Total number of bits to decode. for (int y = 0; y < imgHeight; y += 8) { for (int x = 0; x < imgWidth; x += 8) { int[] blueData = ImageKey.Encoder.GetBlueChannelData(b, x, y); double[] blueDCT = ImageKey.Encoder.DCT(ref blueData); int[] blueDCTI = ImageKey.Encoder.Quantize(ref blueDCT, ref Encoder.Q2); int[] blueDCTC = ImageKey.Encoder.Quantize(ref blueDCT, ref Encoder.Q); if (bitofs < totalBits) GetBits(ref blueDCTI, ref blueDCTC, ref bitofs, ref totalBits, ref codeBytes); } } bitofs = 0; for (int i = 0; i < (expectedLength / Encoder.HIDE_COUNT) * 8; i++) { int bytePos = (bitofs) >> 3; int bitPos = (bitofs) % 8; byte mask = (byte)(1 << bitPos); List<int> values = new List<int>(); int zeroCount = 0; int oneCount = 0; for (int j = 0; j < Encoder.HIDE_COUNT; j++) { int val = (codeBytes[bytePos + ((expectedLength / Encoder.HIDE_COUNT) * j)] & mask) >> bitPos; values.Add(val); if (val == 0) zeroCount++; else oneCount++; } if (oneCount >= zeroCount) outBytes[bytePos] |= mask; bitofs++; values.Clear(); } return (System.Text.Encoding.ASCII.GetString(outBytes)); } public static void GetBits(ref int[] DCTMatrix, ref int[] CMatrix, ref int bitofs, ref int totalBits, ref byte[] codeBytes) { for (int u = 0; u < 8; u++) { for (int v = 0; v < 8; v++) { if ((u != 0 || v != 0) && CMatrix[v + (u * 8)] != 0 && DCTMatrix[v + (u * 8)] != 0) { if (bitofs < totalBits) { int bytePos = (bitofs) >> 3; int bitPos = (bitofs) % 8; byte mask = (byte)(1 << bitPos); int value = DCTMatrix[v + (u * 8)] & (1 << Encoder.HIDE_BIT_POS); if (value != 0) codeBytes[bytePos] |= mask; bitofs++; } } } } } } } UPDATE: By switching to using a QR Code as the source message and swapping a pair of coefficients in each block instead of bit manipulation I've been able to get the message to survive the transform. However to get the message to come through without corruption I have to adjust both coefficients as well as swap them. For example swapping (3,4) and (4,3) in the DCT matrix and then respectively adding 8 and subtracting 8 as an arbitrary constant seems to work. This survives a re-JPEG'ing of 96 but any form of scaling/cropping destroys the message again. I was hoping that by operating on mid to low frequency values that the message would be preserved even under some light image manipulation.

    Read the article

  • Distinct rand() sequences yielding the same results in an expression

    - by suszterpatt
    Ok, this is a really weird one. I have an MPI program, where each process has to generate random numbers in a fixed range (the range is read from file). What happens is that even though I seed each process with a different value, and the numbers generated by rand() are different in each process, the expression to generate the random numbers still yields the same sequence between them. Here's all relevant code: // 'rank' will be unique for each process int rank; MPI_Comm_rank(MPI_COMM_WORLD, &rank); // seed the RNG with a different value for each process srand(time(NULL) + rank); // print some random numbers to see if we get a unique sequence in each process // 'log' is a uniquely named file, each process has its own log << rand() << " " << rand() << " " << rand() << std::endl; // do boring deterministic stuff while (true) { // waitTimeMin and waitTimeMax are integers, Max is always greater than Min waitSecs = waitTimeMin + rand() % (waitTimeMax - waitTimeMin); log << "waiting " << waitSecs << " seconds" << std::endl; sleep(waitSecs); // do more boring deterministic stuff } Here's the output of each process, with 3 processes generating numbers in the range [1,9]. process 1: 15190 28284 3149 waiting 6 seconds waiting 8 seconds waiting 9 seconds waiting 4 seconds process 2: 286 6264 3153 waiting 6 seconds waiting 8 seconds waiting 9 seconds waiting 4 seconds process 3: 18151 17013 3156 waiting 6 seconds waiting 8 seconds waiting 9 seconds waiting 4 seconds So while rand() clearly generates different numbers, the expression to calculate waitSecs still evaluates to the same sequence on all processes. What's even weirder: if I run the program with the same parameteres again, only the first 3 random numbers will change, the rest of the "random" sequence will be exactly the same in each run! Changing the range of numbers will obviously produce a different result from this one, but the same parameters always yield the same sequence, between processes and between executions: except for the first 3 numbers. Just what the hell is going on here?

    Read the article

  • How do I get the next token in a Cstring if I want to use it as an int? (c++)

    - by Van
    My objective is to take directions from a user and eventually a text file to move a robot. The catch is that I must use Cstrings(such as char word[];) rather than the std::string and tokenize them for use. the code looks like this: void Navigator::manualDrive() { char uinput[1]; char delim[] = " "; char *token; cout << "Enter your directions below: \n"; cin.ignore(); cin.getline (uinput, 256); token=strtok(uinput, delim); if(token == "forward") { int inches; inches=token+1; travel(inches); } } I've never used Cstrings I've never tokenized anything before, and I don't know how to write this. Our T.A.'s expect us to google and find all the answers because they are aware we've never been taught these methods. Everyone in my lab is having much more trouble than usual. I don't know the code to write but I know what I want my program to do. I want it to execute like this: 1) Ask for directions. 2) cin.getline the users input 3) tokenize the inputed string 4) if the first word token == "forward" move to the next token and find out how many inches to move forward then move forward 5) else if the first token == "turn" move to the next token. if the next token == "left" move to the next token and find out how many degrees to turn left I will have to do this for forward x, backward x, turn left x, turn right x, and stop(where x is in inches or degrees). I already wrote functions that tell the robot how to move forward an inch and turn in degrees. I just need to know how to convert the inputted strings to all lowercase letters and move from token to token and convert or extract the numbers from the string to use them as integers. If all is not clear you can read my lab write up at this link: http://www.cs.utk.edu/~cs102/robot_labs/Lab9.html If anything is unclear please let me know, and I will clarify as best I can.

    Read the article

  • Deterministic key serialization

    - by Mike Boers
    I'm writing a mapping class which uses SQLite as the storage backend. I am currently allowing only basestring keys but it would be nice if I could use a couple more types hopefully up to anything that is hashable (ie. same requirements as the builtin dict). To that end I would like to derive a deterministic serialization scheme. Ideally, I would like to know if any implementation/protocol combination of pickle is deterministic for hashable objects (e.g. can only use cPickle with protocol 0). I noticed that pickle and cPickle do not match: >>> import pickle >>> import cPickle >>> def dumps(x): ... print repr(pickle.dumps(x)) ... print repr(cPickle.dumps(x)) ... >>> dumps(1) 'I1\n.' 'I1\n.' >>> dumps('hello') "S'hello'\np0\n." "S'hello'\np1\n." >>> dumps((1, 2, 'hello')) "(I1\nI2\nS'hello'\np0\ntp1\n." "(I1\nI2\nS'hello'\np1\ntp2\n." Another option is to use repr to dump and ast.literal_eval to load. This would only be valid for builtin hashable types. I have written a function to determine if a given key would survive this process (it is rather conservative on the types it allows): def is_reprable_key(key): return type(key) in (int, str, unicode) or (type(key) == tuple and all( is_reprable_key(x) for x in key)) The question for this method is if repr itself is deterministic for the types that I have allowed here. I believe this would not survive the 2/3 version barrier due to the change in str/unicode literals. This also would not work for integers where 2**32 - 1 < x < 2**64 jumping between 32 and 64 bit platforms. Are there any other conditions (ie. do strings serialize differently under different conditions)? (If this all fails miserably then I can store the hash of the key along with the pickle of both the key and value, then iterate across rows that have a matching hash looking for one that unpickles to the expected key, but that really does complicate a few other things and I would rather not do it.) Any insights?

    Read the article

  • What are the Options for Storing Hierarchical Data in a Relational Database?

    - by orangepips
    Good Overviews One more Nested Intervals vs. Adjacency List comparison: the best comparison of Adjacency List, Materialized Path, Nested Set and Nested Interval I've found. Models for hierarchical data: slides with good explanations of tradeoffs and example usage Representing hierarchies in MySQL: very good overview of Nested Set in particular Hierarchical data in RDBMSs: most comprehensive and well organized set of links I've seen, but not much in the way on explanation Options Ones I am aware of and general features: Adjacency List: Columns: ID, ParentID Easy to implement. Cheap node moves, inserts, and deletes. Expensive to find level (can store as a computed column), ancestry & descendants (Bridge Hierarchy combined with level column can solve), path (Lineage Column can solve). Use Common Table Expressions in those databases that support them to traverse. Nested Set (a.k.a Modified Preorder Tree Traversal) First described by Joe Celko - covered in depth in his book Trees and Hierarchies in SQL for Smarties Columns: Left, Right Cheap level, ancestry, descendants Compared to Adjacency List, moves, inserts, deletes more expensive. Requires a specific sort order (e.g. created). So sorting all descendants in a different order requires additional work. Nested Intervals Combination of Nested Sets and Materialized Path where left/right columns are floating point decimals instead of integers and encode the path information. Bridge Table (a.k.a. Closure Table: some good ideas about how to use triggers for maintaining this approach) Columns: ancestor, descendant Stands apart from table it describes. Can include some nodes in more than one hierarchy. Cheap ancestry and descendants (albeit not in what order) For complete knowledge of a hierarchy needs to be combined with another option. Flat Table A modification of the Adjacency List that adds a Level and Rank (e.g. ordering) column to each record. Expensive move and delete Cheap ancestry and descendants Good Use: threaded discussion - forums / blog comments Lineage Column (a.k.a. Materialized Path, Path Enumeration) Column: lineage (e.g. /parent/child/grandchild/etc...) Limit to how deep the hierarchy can be. Descendants cheap (e.g. LEFT(lineage, #) = '/enumerated/path') Ancestry tricky (database specific queries) Database Specific Notes MySQL Use session variables for Adjacency List Oracle Use CONNECT BY to traverse Adjacency Lists PostgreSQL ltree datatype for Materialized Path SQL Server General summary 2008 offers HierarchyId data type appears to help with Lineage Column approach and expand the depth that can be represented.

    Read the article

  • Implementing Skip List in C++

    - by trikker
    [SOLVED] So I decided to try and create a sorted doubly linked skip list... I'm pretty sure I have a good grasp of how it works. When you insert x the program searches the base list for the appropriate place to put x (since it is sorted), (conceptually) flips a coin, and if the "coin" lands on a then that element is added to the list above it(or a new list is created with element in it), linked to the element below it, and the coin is flipped again, etc. If the "coin" lands on b at anytime then the insertion is over. You must also have a -infinite stored in every list as the starting point so that it isn't possible to insert a value that is less than the starting point (meaning that it could never be found.) To search for x, you start at the "top-left" (highest list lowest value) and "move right" to the next element. If the value is less than x than you continue to the next element, etc. until you have "gone too far" and the value is greater than x. In this case you go back to the last element and move down a level, continuing this chain until you either find x or x is never found. To delete x you simply search x and delete it every time it comes up in the lists. For now, I'm simply going to make a skip list that stores numbers. I don't think there is anything in the STL that can assist me, so I will need to create a class List that holds an integer value and has member functions, search, delete, and insert. The problem I'm having is dealing with links. I'm pretty sure I could create a class to handle the "horizontal" links with a pointer to the previous element and the element in front, but I'm not sure how to deal with the "vertical" links (point to corresponding element in other list?) If any of my logic is flawed please tell me, but my main questions are: How to deal with vertical links and whether my link idea is correct Now that I read my class List idea I'm thinking that a List should hold a vector of integers rather than a single integer. In fact I'm pretty positive, but would just like some validation. I'm assuming the coin flip would simply call int function where rand()%2 returns a value of 0 or 1 and if it's 0 then a the value "levels up" and if it's 0 then the insert is over. Is this incorrect? How to store a value similar to -infinite? Edit: I've started writing some code and am considering how to handle the List constructor....I'm guessing that on its construction, the "-infinite" value should be stored in the vectorname[0] element and I can just call insert on it after its creation to put the x in the appropriate place.

    Read the article

  • How to check for palindrome using Python logic

    - by DrOnline
    My background is only a 6 month college class in basic C/C++, and I'm trying to convert to Python. I may be talking nonsense, but it seems to me C, at least at my level, is very for-loop intensive. I solve most problems with these loops. And it seems to me the biggest mistake people do when going from C to Python is trying to implement C logic using Python, which makes things run slowly, and it's just not making the most of the language. I see on this website: http://hyperpolyglot.org/scripting (serach for "c-style for", that Python doesn't have C-style for loops. Might be outdated, but I interpret it to mean Python has its own methods for this. I've tried looking around, I can't find much up to date (Python 3) advice for this. How can I solve a palindrome challenge in Python, without using the for loop? I've done this in C in class, but I want to do it in Python, on a personal basis. The problem is from the Euler Project, great site btw. def isPalindrome(n): lst = [int(n) for n in str(n)] l=len(lst) if l==0 || l==1: return True elif len(lst)%2==0: for k in range (l) ##### else: while (k<=((l-1)/2)): if (list[]): ##### for i in range (999, 100, -1): for j in range (999,100, -1): if isPalindrome(i*j): print(i*j) break I'm missing a lot of code here. The five hashes are just reminders for myself. Concrete questions: 1) In C, I would make a for loop comparing index 0 to index max, and then index 0+1 with max-1, until something something. How to best do this in Python? 2) My for loop (in in range (999, 100, -1), is this a bad way to do it in Python? 3) Does anybody have any good advice, or good websites or resources for people in my position? I'm not a programmer, I don't aspire to be one, I just want to learn enough so that when I write my bachelor's degree thesis (electrical engineering), I don't have to simultaneously LEARN an applicable programming language while trying to obtain good results in the project. "How to go from basic C to great application of Python", that sort of thing. 4) Any specific bits of code to make a great solution to this problem would also be appreciated, I need to learn good algorithms.. I am envisioning 3 situations. If the value is zero or single digit, if it is of odd length, and if it is of even length. I was planning to write for loops... PS: The problem is: Find the highest value product of two 3 digit integers that is also a palindrome.

    Read the article

  • Implementing events to communicate between two processes - C

    - by Jamie Keeling
    Hello all! I have an application consisting of two windows, one communicates to the other and sends it a struct constaining two integers (In this case two rolls of a dice). I will be using events for the following circumstances: Process a sends data to process b, process b displays data Process a closes, in turn closing process b Process b closes a, in turn closing process a I have noticed that if the second process is constantly waiting for the first process to send data then the program will be just sat waiting, which is where the idea of implementing threads on each process occurred and I have started to implement this already. The problem i'm having is that I don't exactly have a lot of experience with threads and events so I'm not sure of the best way to actually implement what I want to do. Following is a small snippet of what I have so far in the producer application; Create thread: case IDM_FILE_ROLLDICE: { hDiceRoll = CreateThread( NULL, // lpThreadAttributes (default) 0, // dwStackSize (default) ThreadFunc(hMainWindow), // lpStartAddress NULL, // lpParameter 0, // dwCreationFlags &hDiceID // lpThreadId (returned by function) ); } break; The data being sent to the other process: DWORD WINAPI ThreadFunc(LPVOID passedHandle) { HANDLE hMainHandle = *((HANDLE*)passedHandle); WCHAR buffer[256]; LPCTSTR pBuf; LPVOID lpMsgBuf; LPVOID lpDisplayBuf; struct diceData storage; HANDLE hMapFile; DWORD dw; //Roll dice and store results in variable storage = RollDice(); hMapFile = CreateFileMapping( (HANDLE)0xFFFFFFFF, // use paging file NULL, // default security PAGE_READWRITE, // read/write access 0, // maximum object size (high-order DWORD) BUF_SIZE, // maximum object size (low-order DWORD) szName); // name of mapping object if (hMapFile == NULL) { dw = GetLastError(); MessageBox(hMainHandle,L"Could not create file mapping object",L"Error",MB_OK); return 1; } pBuf = (LPTSTR) MapViewOfFile(hMapFile, // handle to map object FILE_MAP_ALL_ACCESS, // read/write permission 0, 0, BUF_SIZE); if (pBuf == NULL) { MessageBox(hMainHandle,L"Could not map view of file",L"Error",MB_OK); CloseHandle(hMapFile); return 1; } CopyMemory((PVOID)pBuf, &storage, (_tcslen(szMsg) * sizeof(TCHAR))); //_getch(); MessageBox(hMainHandle,L"Completed!",L"Success",MB_OK); UnmapViewOfFile(pBuf); return 0; } I'm trying to find out how I would integrate an event with the threaded code to signify to the other process that something has happened, I've seen an MSDN article on using events but it's just confused me if anything, I'm coming up on empty whilst searching on the internet too. Thanks for any help Edit: I can only use the Create/Set/Open methods for events, sorry for not mentioning it earlier.

    Read the article

  • Schema to support dynamic properties

    - by Johan Fredrik Varen
    Hi people. I'm working on an editor that enables its users to create "object" definitions in real-time. A definition can contain zero or more properties. A property has a name a type. Once a definition is created, a user can create an object of that definition and set the property values of that object. So by the click of a mouse-button, the user should ie. be able to create a new definition called "Bicycle", and add the property "Size" of type "Numeric". Then another property called "Name" of type "Text", and then another property called "Price" of type "Numeric". Once that is done, the user should be able to create a couple of "Bicycle" objects and fill in the "Name" and "Price" property values of each bike. Now, I've seen this feature in several software products, so it must be a well-known concept. My problem started when I sat down and tried to come up with a DB schema to support this data structure, because I want the property values to be stored using the appropriate column types. Ie. a numeric property value is stored as, say, an INT in the database, and a textual property value is stored as VARCHAR. First, I need a table that will hold all my object definitions: Table obj_defs id | name | ---------------- 1 | "Bicycle" | 2 | "Book" | Then I need a table for holding what sort of properties each object definition should have: Table prop_defs id | obj_def_id | name | type | ------------------------------------ 1 | 1 | "Size" | ? | 2 | 1 | "Name" | ? | 3 | 1 | "Price" | ? | 4 | 2 | "Title" | ? | 5 | 2 | "Author" | ? | 6 | 2 | "ISBN" | ? | I would also need a table that holds each object: Table objects id | created | updated | ------------------------------ 1 | 2011-05-14 | 2011-06-15 | 2 | 2011-05-14 | 2011-06-15 | 3 | 2011-05-14 | 2011-06-15 | Finally, I need a table that will hold the actual property values of each object, and one solution is for this table to have one column for each possible value type, such as this: Table prop_vals id | prop_def_id | object_id | numeric | textual | boolean | ------------------------------------------------------------ 1 | 1 | 1 | 27 | | | 2 | 2 | 1 | | "Trek" | | 3 | 3 | 1 | 1249 | | | 4 | 1 | 2 | 26 | | | 5 | 2 | 2 | | "GT" | | 6 | 3 | 2 | 159 | | | 7 | 4 | 3 | | "It" | | 8 | 5 | 3 | | "King" | | 9 | 6 | 4 | 9 | | | If I implemented this schema, what would the "type" column of the prop_defs table hold? Integers that each map to a column name, varchars that simply hold the column name? Any other possibilities? Would a stored procedure help me out here in some way? And what would the SQL for fetching the "name" property of object 2 look like?

    Read the article

< Previous Page | 36 37 38 39 40 41 42 43  | Next Page >