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  • How to find the number of inversions in an array ?

    - by Michael
    This is an phone interview question: "Find the number of inversions in an array". I guess they mean O(N*log N) solution since O(N^2) is trivial. I guess it cannot be better than O(N*log N) since sorting is O(N*log N) I have checked a similar question from SO and can summarize the answers as follows: Calculate half the distance the elements should be moved to sort the array : copy the array and sort the copy. For each element of the original array a[i] find it's position j in the sorted copy (binary search) and sum abs(i - j)/2. Modify merge sort : modify merge to count inversions between two sorted arrays (it takes O(N)) and run merge sort with the modified merge. Does it make sense ? Are there other (maybe simpler) solution ? Isn't it too hard for a phone interview ?

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  • C++ Filling an 1D array to represent a n-dimensional object based on a straight line segment

    - by Ben
    I'm struggling to find a good way to put this question but here goes. I'm making a system that uses a 1D array implemented as double * parts_ = new double[some_variable];. I want to use this to hold co-ordinates for a particle system that can run in various dimensions. What I want to be able to do is write a generic fill algorithm for filling this in n-dimensions with a common increment in all direction to a variable size. Examples will serve best I think. Consider the case where the number of particles stored by the array is 4 In 1D this produces 4 elements in the array because each particle only has one co-ordinate. 1D: {0, 25, 50, 75}; In 2D this produces 8 elements in the array because each particle has two co-ordinates.. 2D: {0, 0, 0, 25, 25, 0, 25, 25} In 3D this produces 12 elements in the array because each particle now has three co-ordinates {0, 0, 0, 0, 0, 25, 0, 0, 50, ... } These examples are still not quite accurate, but they hopefully will suffice. The way I would do this normally for two dimensions: int i = 0; for(int x = 0; x < parts_size_ / dims_ / dims_ * 25; x += 25) { for(int y = 0; y < parts_size_ / dims_ / dims_ * 25; y += 25) { parts_[i] = x; parts_[i+1] = y; i+=2; // Indentation hates me today .< How can I implement this for n-dimensions where 25 can be any number? The straight line part is because it seems to me logical that a line is a somewhat regular shape in 1D, as is a square in 2D, and a cube in 3D. It seems to me that it would follow that there would be similar shapes in this family that could be implemented for 4D and higher dimensions via a similar fill pattern. This is the shape I wish to set my array to represent.

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  • How do you convert an unsigned int[16] of hexidecimal to an unsigned char array without losing any information?

    - by user1068636
    I have a unsigned int[16] array that when printed out looks like this: 4418703544ED3F688AC208F53343AA59 The code used to print it out is this: for (i = 0; i < 16; i++) printf("%X", CipherBlock[i] / 16), printf("%X",CipherBlock[i] % 16); printf("\n"); I need to pass this unsigned int array "CipherBlock" into a decrypt() method that only takes unsigned char *. How do correctly memcpy everything from the "CipherBlock" array into an unsigned char array without losing information? My understanding is an unsigned int is 4 bytes and unsigned char 1 byte. Since "CipherBlock" is 16 unsigned integers, the total size in bytes = 16 * 4 = 64 bytes. Does this mean my unsigned char[] array needs to be 64 in length? If so, would the following work? unsigned char arr[64] = { '\0' }; memcpy(arr,CipherBlock,64); This does not seem to work. For some reason it only copies the the first byte of "CipherBlock" into "arr". The rest of "arr" is '\0' thereafter.

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  • How do I use a contact's photo in a table view cell?

    - by Andy
    I've got an app that has a table view that displays contact information in each row. I'd like to use the contact's stored image (if there is one available) as the image on the left-hand side of the cell. I've found some sketchy sample code in Apple's documentation, but the address book references some kind of weird data type (CFDataRef) that doesn't appear to correspond to the data types referenced in the table view programming guide (mainly UIImage). This seems like a pretty basic task, but I can't seem to wrap my head around it. Thanks in advance for any help you can offer.

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  • how to represent negative number to array of integers ?

    - by stdnoit
    I must convert string of 1324312321 to array of integers in java this is fine. I could use integer parseint and string substring method but how do I repesent -12312312 to my original array of integer.. the fact that - is a char / string and convert to array of integer would alter the value ( even though I convert - to integer-equivalent , it would change the rest of 12312312) it must be an array of integers and how should I convert negative numbers and still keeep the same value somehow reminding me of two complements trick but i dont think i need to go down to binary level in my program.. any other trick for doing this? thanks!

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  • Given an array of arguments, how do I send those arguments to a particular function in Ruby?

    - by Steven Xu
    Forgive the beginner question, but say I have an array: a = [1,2,3] And a function somewhere; let's say it's an instance function: class Ilike def turtles(*args) puts args.inspect end end How do I invoke Ilike.turtles with a as if I were calling (Ilike.new).turtles(1,2,3). I'm familiar with send, but this doesn't seem to translate an array into an argument list. A parallel of what I'm looking for is the Javascript apply, which is equivalent to call but converts the array into an argument list.

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  • How detect length of a numpy array with only one element?

    - by mishaF
    I am reading in a file using numpy.genfromtxt which brings in columns of both strings and numeric values. One thing I need to do is detect the length of the input. This is all fine provided there are more than one value read into each array. But...if there is only one element in the resulting array, the logic fails. I can recreate an example here: import numpy as np a = np.array(2.3) len(a) returns an error saying: TypeError: len() of unsized object however, If a has 2 or more elements, len() behaves as one would expect. import numpy as np a = np.array([2.3,3.6]) len(a) returns 2 My concern here is, if I use some strange exception handling, I can't distinguish between a being empty and a having length = 1.

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  • How can I pass an array resulting from a Perl method by reference?

    - by arareko
    Some XML::LibXML methods return arrays instead of references to arrays. Instead of doing this: $self->process_items($xml->findnodes('items/item')); I want to do something like: $self->process_items(\$xml->findnodes('items/item')); So that in process_items() I can dereference the original array instead of creating a copy: sub process_items { my ($self, $items) = @_; foreach my $item (@$items) { # do something... } } I can always store the results of findnodes() into an array and then pass the array reference to my own method, but let's say I want to try a reduced version of my code. Is that the correct syntax for passing the method results or should I use something different? Thanks! EDIT: Now suppose I want to change process_items() to process_item() so I can do stuff on a single element of the referenced array inside a loop. Something like: $self->process_item($_) for ([ $xml->findnodes('items/item') ]); This doesn't work as process_item() is executed only once because a single value is passed to the for loop (the reference to the array from findnodes()). What's the proper way of using $_ in this case?

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  • JavaScript: Is there a better way to retain your array but efficiently concat or replace items?

    - by Michael Mikowski
    I am looking for the best way to replace or add to elements of an array without deleting the original reference. Here is the set up: var a = [], b = [], c, i, obj; for ( i = 0; i < 100000; i++ ) { a[ i ] = i; b[ i ] = 10000 - i; } obj.data_list = a; Now we want to concatenate b INTO a without changing the reference to a, since it is used in obj.data_list. Here is one method: for ( i = 0; i < b.length; i++ ) { a.push( b[ i ] ); } This seems to be a somewhat terser and 8x (on V8) faster method: a.splice.apply( a, [ a.length, 0 ].concat( b ) ); I have found this useful when iterating over an "in-place" array and don't want to touch the elements as I go (a good practice). I start a new array (let's call it keep_list) with the initial arguments and then add the elements I wish to retain. Finally I use this apply method to quickly replace the truncated array: var keep_list = [ 0, 0 ]; for ( i = 0; i < a.length; i++ ){ if ( some_condition ){ keep_list.push( a[ i ] ); } // truncate array a.length = 0; // And replace contents a.splice.apply( a, keep_list ); There are a few problems with this solution: there is a max call stack size limit of around 50k on V8 I have not tested on other JS engines yet. This solution is a bit cryptic Has anyone found a better way?

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  • Mathematica quickie: About making cells Input cells by default.

    - by andrz
    I'm going through some lecture notes, Fundamentals of Mathematica Programming (see the .nb file there). I'd like to be able to do the exercises right there in the notebook; but for some reason I can't figure out how to make the default cell an Input cell. In other words, when I'm clicking in that notebook to create a new cell--in the exercises--the cell is by default a text cell. I'd like for it to be an Input cell so that I don't have to manually change it each time. Ideas?

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  • Excel Shows "#########" when i try to write DateTime.Now.tostring() to one of the cell in Excel File

    - by user1209631
    I have created a application in c# , it reads excel file and after checking some conditions, it select a row to be written in another Excel File. Everything is working fine, but i need to end the file with the DateTime.Now.ToString(). string date = DateTime.Now.ToString(); ExcelWorkSheet2.Cells[newFileRow, 1] = date; When I see the file created, it shows "########" symbol instead of actual date. When I select that cell , it changes to correct date format. What may be going wrong?

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  • Java JTable, how to change cell data (write text in)?

    - by Bob Owuor
    Am looking to change a cell's data in a jtable. How can I do this? When I execute the following code I get errors. JFrame f= new JFrame(); final JTable table= new JTable(10,5); TableModelListener tl= new TableModelListener(){ public void tableChanged(TableModelEvent e){ table.setValueAt("hello world",2,2); } }; table.getModel().addTableModelListener(tl); f.add(table); f.pack(); f.setVisible(true); I have also tried this below but it still doesn't work. What gives? table.getModel().setValueAt("hello world",2,2);

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  • Which of these Array Initializations is better in Ruby?

    - by Bragaadeesh
    Hi, Which of these two forms of Array Initialization is better in Ruby? Method 1: DAYS_IN_A_WEEK = (0..6).to_a HOURS_IN_A_DAY = (0..23).to_a @data = Array.new(DAYS_IN_A_WEEK.size).map!{ Array.new(HOURS_IN_A_DAY.size) } DAYS_IN_A_WEEK.each do |day| HOURS_IN_A_DAY.each do |hour| @data[day][hour] = 'something' end end Method 2: DAYS_IN_A_WEEK = (0..6).to_a HOURS_IN_A_DAY = (0..23).to_a @data = {} DAYS_IN_A_WEEK.each do |day| HOURS_IN_A_DAY.each do |hour| @data[day] ||= {} @data[day][hour] = 'something' end end The difference between the first method and the second method is that the second one does not allocate memory initially. I feel the second one is a bit inferior when it comes to performance due to the numerous amount of Array copies that has to happen. However, it is not straight forward in Ruby to find what is happening. So, if someone can explain me which is better, it would be really great! Thanks

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  • My table cells don't highlight immediately when touched

    - by Steve Denenberg
    Hi, In my app, I have a table view that has about eight cells. There is a navigation bar at the top. When a user touches a cell, nothing happens for about 1/2 second. Then the touched cell highlights blue and immediately the new view slides into position. The problem is that there is no feedback to the user about which cell he touched until just before the new view slides into position. For example, when I explore the tables in the iPhone's Settings application, when you touch a cell, the cell immediately turns blue, and then there is a 1/2 second delay, and then you see the new view. How do I get my table's feedback of highlighting the cells to happen immediately? I am using tableView didSelectRowAtIndexPath:, and each cell has an accessory button. Thanks for any insight.

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  • What's the best way to have functions share an array in Objective-C?

    - by editor
    I understand that in Objective-C you declare an array in the header file and interact with it in a class. So far I'm adding things and fetching them fine within a single function. I'm new to the language however and can't figure out how to share that array across other functions. I'd like to initialize array data in my viewDidLoad and access it from various functions later on. Is this possible and if so what's the best way to do it?

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  • php: possible to convert array of numbers to 'from' and 'to' pairs where consecutive?

    - by Haroldo
    I have an array of timestamps referring to the days when a holiday home is booked. each timestamp is a round day. I want to turn this into an array of 'begins' and 'ends' pairs for consecutive dates Are there any php functions I should be aware of for writing this function? Or does anyone have any pointers for this kind of thing? thanks! edit: example array: Array ( [0] => 1273536000 [1] => 1273622400 [2] => 1273708800 [3] => 1273795200 [4] => 1273881600 [5] => 1273968000 [6] => 1274054400 [7] => 1274140800 [8] => 1274227200 ) where a day = 86400 (seconds)

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  • C# IndexOutOfRange issue, probably simple.

    - by MWC
    Banging my head off the wall due to this. I'm getting the error at cell[rcell] = repack[counter] even though I have 190 items in the repack array. private string csvtogrid(string input) { input = input.Replace("\r", ",").Substring(2).TrimEnd(',').Trim().Replace("\n", ",").Replace(",,,", ",").Replace(",,",","); string[] repack = input.Split(','); string[] cell = { }; int rcell = 1; for (int counter = 1; counter < repack.Length; counter++) { if (rcell < 4) { cell[rcell] = repack[counter]; rcell++; } procgrid.Rows.Add(cell[1], cell[2], cell[3]); rcell = 1; } richTextBox1.Text = input; return null; }

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  • JavaScript: String Concatenation slow performance? Array.join('')?

    - by NickNick
    I've read that if I have a for loop, I should not use string concation because it's slow. Such as: for (i=0;i<10000000;i++) { str += 'a'; } And instead, I should use Array.join(), since it's much faster: var tmp = []; for (i=0;i<10000000;i++) { tmp.push('a'); } var str = tmp.join(''); However, I have also read that string concatention is ONLY a problem for Internet Explorer and that browsers such as Safari/Chrome, which use Webkit, actually perform FASTER is using string concatention than Array.join(). I've attempting to find a performance comparison between all major browser of string concatenation vs Array.join() and haven't been able to find one. As such, what is faster and more efficient JavaScript code? Using string concatenation or Array.join()?

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  • Drupal: Create custom search

    - by Dr. Hfuhruhurr
    I'm trying to create a custom search but getting stuck. What I want is to have a dropdownbox so the user can choose where to search in. These options can mean 1 or more content types. So if he chooses options A, then the search will look in node-type P,Q,R. But he may not give those results, but only the uid's which will be then themed to gather specific data for that user. To make it a little bit clearer, Suppose I want to llok for people. The what I'm searching in is 2 content profile types. But ofcourse you dont want to display those as a result, but a nice picture of the user and some data. I started with creating a form with a textfield and the dropdown box. Then, in the submit handler, i created the keys and redirected to another pages with those keys as a tail. This page has been defined in the menu hook, just like how search does it. After that I want to call hook_view to do the actual search by calling node_search, and give back the results. Unfortunately, it goes wrong. When i click the Search button, it gives me a 404. But am I on the right track? Is this the way to create a custom search? Thx for your help. Here's the code for some clarity: <?php // $Id$ /* * @file * Searches on Project, Person, Portfolio or Group. */ /** * returns an array of menu items * @return array of menu items */ function vm_search_menu() { $subjects = _vm_search_get_subjects(); foreach ($subjects as $name => $description) { $items['zoek/'. $name .'/%menu_tail'] = array( 'page callback' => 'vm_search_view', 'page arguments' => array($name), 'type' => MENU_LOCAL_TASK, ); } return $items; } /** * create a block to put the form into. * @param $op * @param $delta * @param $edit * @return mixed */ function vm_search_block($op = 'list', $delta = 0, $edit = array()) { switch ($op) { case 'list': $blocks[0]['info'] = t('Algemene zoek'); return $blocks; case 'view': if (0 == $delta) { $block['subject'] = t(''); $block['content'] = drupal_get_form('vm_search_general_form'); } return $block; } } /** * Define the form. */ function vm_search_general_form() { $subjects = _vm_search_get_subjects(); foreach ($subjects as $key => $subject) { $options[$key] = $subject['desc']; } $form['subjects'] = array( '#type' => 'select', '#options' => $options, '#required' => TRUE, ); $form['keys'] = array( '#type' => 'textfield', '#required' => TRUE, ); $form['submit'] = array( '#type' => 'submit', '#value' => t('Zoek'), ); return $form; } function vm_search_general_form_submit($form, &$form_state) { $subjects = _vm_search_get_subjects(); $keys = $form_state['values']['keys']; //the search keys //the content types to search in $keys .= ' type:' . implode(',', $subjects[$form_state['values']['subjects']]['types']); //redirect to the page, where vm_search_view will handle the actual search $form_state['redirect'] = 'zoek/'. $form_state['values']['subjects'] .'/'. $keys; } /** * Menu callback; presents the search results. */ function vm_search_view($type = 'node') { // Search form submits with POST but redirects to GET. This way we can keep // the search query URL clean as a whistle: // search/type/keyword+keyword if (!isset($_POST['form_id'])) { if ($type == '') { // Note: search/node can not be a default tab because it would take on the // path of its parent (search). It would prevent remembering keywords when // switching tabs. This is why we drupal_goto to it from the parent instead. drupal_goto($front_page); } $keys = search_get_keys(); // Only perform search if there is non-whitespace search term: $results = ''; if (trim($keys)) { // Log the search keys: watchdog('vm_search', '%keys (@type).', array('%keys' => $keys, '@type' => $type)); // Collect the search results: $results = node_search('search', $type); if ($results) { $results = theme('box', t('Zoek resultaten'), $results); } else { $results = theme('box', t('Je zoek heeft geen resultaten opgeleverd.')); } } } return $results; } /** * returns array where to look for * @return array */ function _vm_search_get_subjects() { $subjects['opdracht'] = array('desc' => t('Opdracht'), 'types' => array('project') ); $subjects['persoon'] = array('desc' => t('Persoon'), 'types' => array('types_specialisatie', 'smaak_en_interesses') ); $subjects['groep'] = array('desc' => t('Groep'), 'types' => array('Villamedia_groep') ); $subjects['portfolio'] = array('desc' => t('Portfolio'), 'types' => array('artikel') ); return $subjects; }

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  • Possible to migrate from non-RAID to RAID 1 and then RAID 5?

    - by stueng
    Using software RAID only Is it possible to start with a 2TB disk full of data and safely add it to a RAID 1 array? Is it then possible to add a third disk and migrate the RAID 1 array into a RAID 5 array? OR Is it possible to start with a 2 disk degraded RAID 5 array and then add the third disk later to create a health RAID 5 array? Backstory: I wish to migrate from a 2 disk NAS (RAID 1) to a 3 disk NAS and only purchase one new disk in doing so

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  • Initialize array in amortized constant time -- what is this trick called?

    - by user946850
    There is this data structure that trades performance of array access against the need to iterate over it when clearing it. You keep a generation counter with each entry, and also a global generation counter. The "clear" operation increases the generation counter. On each access, you compare local vs. global generation counters; if they differ, the value is treated as "clean". This has come up in this answer on Stack Overflow recently, but I don't remember if this trick has an official name. Does it? One use case is Dijkstra's algorithm if only a tiny subset of the nodes has to be relaxed, and if this has to be done repeatedly.

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