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  • Array: Recursive problem cracked me up

    - by VaioIsBorn
    An array of integers A[i] (i 1) is defined in the following way: an element A[k] ( k 1) is the smallest number greater than A[k-1] such that the sum of its digits is equal to the sum of the digits of the number 4* A[k-1] . You need to write a program that calculates the N th number in this array based on the given first element A[1] . INPUT: In one line of standard input there are two numbers seperated with a single space: A[1] (1 <= A[1] <= 100) and N (1 <= N <= 10000). OUTPUT: The standard output should only contain a single integer A[N] , the Nth number of the defined sequence. Input: 7 4 Output: 79 Explanation: Elements of the array are as follows: 7, 19, 49, 79... and the 4th element is solution. I tried solving this by coding a separate function that for a given number A[k] calculates the sum of it's digits and finds the smallest number greater than A[k-1] as it says in the problem, but with no success. The first testing failed because of a memory limit, the second testing failed because of a time limit, and now i don't have any possible idea how to solve this. One friend suggested recursion, but i don't know how to set that. Anyone who can help me in any way please write, also suggest some ideas about using recursion/DP for solving this problem. Thanks.

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  • Help me write my LISP :) LISP environments, Ruby Hashes...

    - by MikeC8
    I'm implementing a rudimentary version of LISP in Ruby just in order to familiarize myself with some concepts. I'm basing my implementation off of Peter Norvig's Lispy (http://norvig.com/lispy.html). There's something I'm missing here though, and I'd appreciate some help... He subclasses Python's dict as follows: class Env(dict): "An environment: a dict of {'var':val} pairs, with an outer Env." def __init__(self, parms=(), args=(), outer=None): self.update(zip(parms,args)) self.outer = outer def find(self, var): "Find the innermost Env where var appears." return self if var in self else self.outer.find(var) He then goes on to explain why he does this rather than just using a dict. However, for some reason, his explanation keeps passing in through my eyes and out through the back of my head. Why not use a dict, and then inside the eval function, when a new "sub-environment" needs to be created, just take the existing dict and update the key/value pairs that need to be updated, and pass that new dict into the next eval? Won't the Python interpreter keep track of the previous "outer" envs? And won't the nature of the recursion ensure that the values are pulled out from "inner" to "outer"? I'm using Ruby, and I tried to implement things this way. Something's not working though, and it might be because of this, or perhaps not. Here's my eval function, env being a regular Hash: def eval(x, env = $global_env) ........ elsif x[0] == "lambda" then ->(*args) { eval(x[2], env.merge(Hash[*x[1].zip(args).flatten(1)])) } ........ end The line that matters of course is the "lambda" one. If there is a difference, what's importantly different between what I'm doing here and what Norvig did with his Env class? If there's no difference, then perhaps someone can enlighten me as to why Norvig uses the Env class. Thanks :)

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  • Sparse linear program solver

    - by Jacob
    This great SO answer points to a good sparse solver, but I've got constraints on x (for Ax = b) such that each element in x is >=0 an <=N. The first thing which comes to mind is an LP solver for large sparse matrices. Any ideas/recommendations?

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  • How exactly do MbUnit's [Parallelizable] and DegreeOfParallelism work?

    - by BenA
    I thought I understood how MbUnit's parallel test execution worked, but the behaviour I'm seeing differs sufficiently much from my expectation that I suspect I'm missing something! I have a set of UI tests that I wish to run concurrently. All of the tests are in the same assembly, split across three different namespaces. All of the tests are completely independent of one another, so I'd like all of them to be eligible for parallel execution. To that end, I put the following in the AssemblyInfo.cs: [assembly: DegreeOfParallelism(8)] [assembly: Parallelizable(TestScope.All)] My understanding was that this combination of assembly attributes should cause all of the tests to be considered [Parallelizable], and that the test runner should use 8 threads during execution. My individual tests are marked with the [Test] attribute, and nothing else. None of them are data-driven. However, what I actually see is at most 5-6 threads being used, meaning that my test runs are taking longer than they should be. Am I missing something? Do I need to do anything else to ensure that all of my 8 threads are being used by the runner? N.B. The behaviour is the same irrespective of which runner I use. The GUI, command line and TD.Net runners all behave the same as described above, again leading me to think I've missed something. EDIT: As pointed out in the comments, I'm running v3.1 of MbUnit (update 2 build 397). The documentation suggests that the assembly level [parallelizable] attribute is available, but it does also seem to reference v3.2 of the framework despite that not yet being available. EDIT 2: To further clarify, the structure of my assembly is as follows: assembly - namespace - fixture - tests (each carrying only the [Test] attribute) - fixture - tests (each carrying only the [Test] attribute) - namespace - fixture - tests (each carrying only the [Test] attribute) - fixture - tests (each carrying only the [Test] attribute) - namespace - fixture - tests (each carrying only the [Test] attribute) - fixture - tests (each carrying only the [Test] attribute)

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  • How to initialize F# list when size is unknown, using while..do loop

    - by James Black
    I have a function that will parse the results of a DataReader, and I don't know how many items are returned, so I want to use a while..do loop to iterate over the reader, and the outcome should be a list of a certain type. (fun(reader) -> [ while reader.Read() do new CityType(Id=(reader.GetInt32 0), Name=(reader.GetString 1), StateName=(reader.GetString 2)) ]) This is what I tried, but the warning I get is: This expression should have type 'unit', but has type 'CityType'. Use 'ignore' to discard the result of the expression, or 'let' to bind the result to a name. So what is the best way to iterate over a DataReader and create a list?

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  • How to modify Keyboard interrupt (under Windows XP) from a C++ Program ?

    - by rockr90
    Hi everyone ! We have been given a little project (As part of my OS course) to make a Windows program that modifies keyboard input, so that it transforms any lowercase character entered into an uppercase one (without using caps-lock) ! so when you type on the keyboard you'll see what you're typing transformed into uppercase ! I have done this quite easily using Turbo C by calling geninterrupt() and using variables _AH, _AL, i had to read a character using: _AH = 0x07; // Reading a character without echo geninterrupt(0x21); // Dos interrupt Then to transform it into an Upercase letter i have to mask the 5th bit by using: _AL = _AL & 0xDF; // Masking the entered character with 11011111 and then i will display the character using any output routine. Now, this solution will only work under old C DOS compilers. But what we intend to do is to make a close or similar solution to this by using any modern C/C++ compiler under Windows XP ! What i have first thought of is modifying the Keyboard ISR so that it masks the fifth bit of any entered character to turn it uppercase ! But i do not know how exactly to do this. Second, I wanted to create a Win32 console program to either do the same solution (but to no avail) or make a windows-compatible solution, still i do not know which functions to use ! Third I thought to make a windows program that modifies the ISR directly to suit my needs ! and i'm still looking for how to do this ! So please, If you could help me out on this, I would greatly appreciate it ! Thank you in advance ! (I'm using Windows XP on intel X86 with mingw-GCC compiler.)

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  • Manifesto for Integrated Development Environments

    - by Hugo S Ferreira
    Have you recently take a peek at Coda, or Espresso, or Textmate? Or even Google Chrome's Developer Tools? They are well designed, intuitive, interface rich, and extensible. But Coda, Espresso or Textmate, among several, are text editors, not IDEs. On the other side, VIM and Emacs live in the last century, and Eclipse is an overbloated platform. This is more like an outcry for a decent, common infrastructure for REAL IDEs. But there's some questions attached: (i) what features are needed for such a product and (ii) what products are out there that could fullfil this need, and what are they missing. So here's my draft for a manifesto: Manifesto for Integrated Development Environments: We favor interactivity and productivity over syntax and tools. We favor inline, contextual documentation over man and html files. We favor high-definition, graphic-capable color screens over 80x25 character terminals. We favor the use of advanced input schemas over unintuitive keyboard shortcuts. We favor a common, extensible and customizable infrastructure over unmaintained chaintools. We know the difference between search&replace and refactoring. We know the difference between integrated debugging support over a terminal window. We know the difference between semantic-aware code-completion over dumb textual templates. We favor the usage of standards like (E)BNF.

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  • Supporting Piping (A Useful Hello World)

    - by blastthisinferno
    I am trying to write a collection of simple C++ programs that follow the basic Unix philosophy by: Make each program do one thing well. Expect the output of every program to become the input to another, as yet unknown, program. I'm having an issue trying to get the output of one to be the input of the other, and getting the output of one be the input of a separate instance of itself. Very briefly, I have a program add which takes arguments and spits out the summation. I want to be able to pipe the output to another add instance. ./add 1 2 | ./add 3 4 That should yield 6 but currently yields 10. I've encountered two problems: The cin waits for user input from the console. I don't want this, and haven't been able to find a simple example showing a the use of standard input stream without querying the user in the console. If someone knows of an example please let me know. I can't figure out how to use standard input while supporting piping. Currently, it appears it does not work. If I issue the command ./add 1 2 | ./add 3 4 it results in 7. The relevant code is below: add.cpp snippet // ... COMMAND LINE PROCESSING ... std::vector<double> numbers = multi.getValue(); // using TCLAP for command line parsing if (numbers.size() > 0) { double sum = numbers[0]; double arg; for (int i=1; i < numbers.size(); i++) { arg = numbers[i]; sum += arg; } std::cout << sum << std::endl; } else { double input; // right now this is test code while I try and get standard input streaming working as expected while (std::cin) { std::cin >> input; std::cout << input << std::endl; } } // ... MORE IRRELEVANT CODE ... So, I guess my question(s) is does anyone see what is incorrect with this code in order to support piping standard input? Are there some well known (or hidden) resources that explain clearly how to implement an example application supporting the basic Unix philosophy? @Chris Lutz I've changed the code to what's below. The problem where cin still waits for user input on the console, and doesn't just take from the standard input passed from the pipe. Am I missing something trivial for handling this? I haven't tried Greg Hewgill's answer yet, but don't see how that would help since the issue is still with cin. // ... COMMAND LINE PROCESSING ... std::vector<double> numbers = multi.getValue(); // using TCLAP for command line parsing double sum = numbers[0]; double arg; for (int i=1; i < numbers.size(); i++) { arg = numbers[i]; sum += arg; } // right now this is test code while I try and get standard input streaming working as expected while (std::cin) { std::cin >> arg; std::cout << arg << std::endl; } std::cout << sum << std::endl; // ... MORE IRRELEVANT CODE ...

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  • Call a function from another Class - Obj C

    - by AndrewDK
    I'm trying to figure out how I can call a function from another one of my classes. I'm using a RootViewController to setup one of my views as lets say AnotherViewController So in my AnotherViewController im going to add in on the .h file @class RootViewController And in the .m file im going to import the View #import "RootViewController.h" I have a function called: -(void)toggleView { //do something } And then in my AnotherViewController I have a button assigned out as: -(void)buttonAction { //} In the buttonAction I would like to be able to call the function toggleView in my RootViewController. Can someone clarify on how I do this. I've tried adding this is my buttonAction: RootViewController * returnRootObject = [[RootViewController alloc] init]; [returnRootObject toggleView]; But I dont think that's right. Thanks in advanced.

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  • How to use boost::transform_iterator to iterate over modifed std::map values?

    - by Frank
    I have an std::map, and I would like to define an iterator that returns modified values. Typically, a std::map<int,double>::iterator iterates over std::pair<int,double>, and I would like the same behavior, just the double value is multiplied by a constant. I tried it with boost::transform_iterator, but it doesn't compile: #include <map> #include <boost/iterator/transform_iterator.hpp> #include <boost/functional.hpp> typedef std::map<int,double> Map; Map m; m[100] = 2.24; typedef boost::binder2nd< std::multiplies<double> > Function; typedef boost::transform_iterator<Function, Map::value_type*> MultiplyIter; MultiplyIter begin = boost::make_transform_iterator(m.begin(), Function(std::multiplies<double>(), 4)); // now want to similarly create an end iterator // and then iterate over the modified map The error is: error: conversion from 'boost ::transform_iterator< boost::binder2nd<multiplies<double> >, gen_map<int, double>::iterator , boost::use_default, boost::use_default >' to non-scalar type 'boost::transform_iterator< boost::binder2nd<multiplies<double> >, pair<const int, double> * , boost::use_default, boost::use_default >' requested What is gen_map and do I really need it? I adapted the transform_iterator tutorial code from here to write this code ...

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  • Simple IF statement question

    - by JGreig
    How can I simply the below if statements? if ( isset(var1) & isset(var2) ) { if ( (var1 != something1) || (var2 != something2) ) { // ... code ... } } Seems like this could be condensed to only one IF statement but am not certain if I'd use an AND or OR

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  • What production software have you written in F# in the past year or so that you would previously hav

    - by Peter McGrattan
    Over the last few years F# has evolved into one of Microsoft's fully supported languages employing many ideas incubated in OCaml, ML and Haskell. Over the last several years C# has extended it's general purpose features by introducing more and more functional language features: LINQ (list comprehension), Lamdas, Closures, Anonymous Delegates and more... Given C#'s adoption of these functional features and F#'s taxonomy as an impure functional language (it allows YOU to access framework libraries or change shared state when a function is called if you want to) there is a strong similarity between the two languages although each has it's own polar opposite primary emphasis. I'm interested in any successful models employing these two languages in your production polyglot programs and also the areas within production software (web apps, client apps, server apps) you have written in F# in the past year or so that you would previously have written in C#.

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  • java string detection of ip

    - by user384706
    Hi, Assume a java string that contains an IP (v4 or v6) or a hostname. What is the best way to detect among these cases? I am not interested so much on whether the IP is in valid range (e.g. 999.999.999.999 for IPv4). I am interested in just a way to detect if a String is a hostname or an IP (v4 or v6). Initially I though this: if(theString.indexOf("@")!=-1){ //Not an Ip } but I am not sure if I should always expect a format containing @ always. Thanks

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  • Is learning C++ a good idea?

    - by chang
    The more I hear and read about C++ (e.g. this: http://lwn.net/Articles/249460/), I get the impression, that I'd waste my time learning C++. I some wrote network routing algorithm in C++ for a simulator, and it was a pain (as expected, especially coming from a perl/python/Java background ...). I'm never happy about giving up on some technology, but I would be happy, if I could limit my knowledge of C-family languages to just C, C# and Objective-C (even OS Xs Cocoa, which is huge and takes a lot of time to learn looks like joy compared to C++ ...). Do I need to consider myself dumb or unwilling, just because I'm not partial to the pain involved learning this stuff? Technologies advance and there will be options other than C++, when deciding on implementation languages, or not? And for speed: If speed were that critical, I'd go for a plain C implementation instead, or write C extensions for much more productive languages like ruby or python ... The one-line version of the above: Will C++ stay such a relevant language that every committed programmer should be familiar with it? [ edit / thank you very much for your interesting and useful answers so far .. ] [ edit / .. i am accepting the top-rated answer; thanks again for all answers! ]

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  • Functional languages & support for memoization

    - by Joel
    Do any of the current crop of popular functional languages have good support for memoization & if I was to pick one on the strength of its memoisation which would you recommend & why? Update: I'm looking to optimise a directed graph (where nodes could be functions or data). When a node in the graph is updated I would like the values of other nodes to be recalculated only if they depend the node that changed. Update2: require free or open-source language/runtime.

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  • What alternative is there to writing a TCP/IP data relay?

    - by LoudNPossiblyRight
    I am about to write a tcp/ip data relay - application that passes a one way stream of data from one host/port to another host/port. Initially it will be generic, but later on i will customize it to the need of a specific business request. I am guessing that something generic already exists out there so my question is: Has anyone used a third party (preferably open source) data relay in a production environment, if so what is, and do you recommend it? Any platform is fine. Thanks.

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  • how to create http headers from scratch

    - by Sean Ochoa
    So, I made a simple socket server using python. And now I'm trying to structure a proper http response. However, I can't seem to find any sort of tutorial or spec that discusses how to format http responses. Could someone point me to the right place?

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  • MySQL: Get only count of result set.

    - by Varun
    I am using MVC with PHP/MySQL. Suppose I am using 10 functions with different queries for fetching details from the database. But at other times I may want to get only the count of the result that will be returned by the query. What is the standard way to handle such situation. Should I write 10 more functions which duplicate almost whole query and return only the count. Or Should I always return the count also with the result set Or I can pass a flag to indicate that the function should return count only, and then based on the flag I will dynamically generate the (select part of) query. Or Is there a better way?

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  • How can I pass methods in javascript?

    - by peterjwest
    I often need to pass methods from objects into other objects. However I usually want the method to be attached to the original object (by attached I mean 'this' should refer to the original object). I know a few ways to do this: a) In the object constructor: ObjectA = function() { var that = this; var method = function(a,b,c) { that.abc = a+b+c }} b) In objectA which has been passed objectB: objectB.assign(function(a,b,c) { that.method(a,b,c) }) c) Outside both objects: objectB.assign(function(a,b,c) { objectA.method(a,b,c) }) I want to know if there is a simpler way to pass methods attached to their original objects.

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