[QuickGraph][1]

QuickGraph is a graph library for .NET that is inspired by Boost Graph Library.

QuickGraph provides generic directed/undirected graph datastructures and algorithms for .Net 2.0 and up. QuickGraph comes with algorithms such as depth first seach, breath first search, A* search, shortest path, k-shortest path, maximum flow, minimum spanning tree, least common ancestors, etc... QuickGraph supports MSAGL, GLEE, and Graphviz to render the graphs, serialization to GraphML, etc...

---

There are several ways to build graphs. The C++ Boost Graph Library (BGL) would be your best reference. It implements both adjacency-list, adjacency-matrix and edge-list graphs.
Look [here][2] for details.


  [1]: https://github.com/YaccConstructor/QuickGraph
  [2]: http://www.boost.org/doc/libs/1_47_0/libs/graph/doc/index.html

There is actually a fairly old article in MSDN that covers graph creation in C#, [An Extensive Examination of Data Structures Using C# 2.0]. Despite its age, it still addresses your question as long as you don&#39;t mind creating your own graph class(es).

[An Extensive Examination of Data Structures Using C# 2.0]: http://msdn.microsoft.com/en-us/library/ms379574(v=vs.80).aspx#datastructures20_5_topic3



Under active development, there is https://www.nuget.org/packages/QuikGraph You can view source code on GitHub https://github.com/KeRNeLith/QuikGraph and also read the wiki https://github.com/KeRNeLith/QuikGraph/wiki

I would like an explanation for the values used with the .cfi_def_cfa_offset directives in assembly generated by GCC. I know vaguely that the .cfi directives are involved in call frames and stack unwinding, but I would like a more detailed explanation of why, for example, the values 16 and 8 are used in the assembly outputted by GCC in compiling the following C program on my 64-bit Ubuntu machine.

The C program:

    #include &lt;stdio.h&gt;
    
    int main(int argc, char** argv)
    {
            printf(&quot;%d&quot;, 0);
            return 0;
    }

I invoked GCC on the source file test.c as follows: `gcc -S -O3 test.c`. I know that -O3 enables nonstandard optimization, but I wanted to limit the size of the generated assembly for the sake of brevity.

The generated assembly:


            .file   &quot;test.c&quot;
            .section        .rodata.str1.1,&quot;aMS&quot;,@progbits,1
    .LC0:
            .string &quot;%d&quot;
            .text
            .p2align 4,,15
    .globl main
            .type   main, @function
    main:
    .LFB22:
            .cfi_startproc
            subq    $8, %rsp
            .cfi_def_cfa_offset 16
            xorl    %edx, %edx
            movl    $.LC0, %esi
            movl    $1, %edi
            xorl    %eax, %eax
            call    __printf_chk
            xorl    %eax, %eax
            addq    $8, %rsp
            .cfi_def_cfa_offset 8
            ret
                .cfi_endproc
    .LFE22:
            .size   main, .-main
            .ident  &quot;GCC: (Ubuntu/Linaro 4.5.2-8ubuntu4) 4.5.2&quot;
            .section        .note.GNU-stack,&quot;&quot;,@progbits

Why are the values 16 and 8 used for the .cfi_def_cfa_offset directives in the generated assembly? Also, why is the number 22 used for the local function begin and function end labels?

GAS: Explanation of .cfi_def_cfa_offset

I wrote a java program to test RESTful web services by using Netbeans7.0.1 and it works fine there. Now I wrote the build.xml file to compile the code and when I try to run the generated .class file I always got this exception:

	Exception in thread &quot;main&quot; java.lang.NoClassDefFoundError: ClientREST (wrong name: clientrest/ClientREST)
		at java.lang.ClassLoader.defineClass1(Native Method)
		at java.lang.ClassLoader.defineClassCond(ClassLoader.java:632)
		at java.lang.ClassLoader.defineClass(ClassLoader.java:616)
		at java.security.SecureClassLoader.defineClass(SecureClassLoader.java:141)
		at java.net.URLClassLoader.defineClass(URLClassLoader.java:283)
		at java.net.URLClassLoader.access$000(URLClassLoader.java:58)
		at java.net.URLClassLoader$1.run(URLClassLoader.java:197)
		at java.security.AccessController.doPrivileged(Native Method)
		at java.net.URLClassLoader.findClass(URLClassLoader.java:190)
		at java.lang.ClassLoader.loadClass(ClassLoader.java:307)
		at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:301)
		at java.lang.ClassLoader.loadClass(ClassLoader.java:248)
	Could not find the main class: ClientREST. Program will exit.

The name and path are correct, so any thoughts why I&#39;m getting this exception?



NoClassDefFoundError: wrong name

I tried to find a graph data structure to reuse in C# without any success. Of course, I can borrow from data structure books but I want it to be more commercially practical(?) Also I would appreciate if you can tell me what the best way of implementing a graph is. Thanks 

Is there any graph data structure implemented for C#

<p>I tried to find a graph data structure to reuse in C# without any success. Of course, I can borrow from data structure books but I want it to be more commercially practical(?) Also I would appreciate if you can tell me what the best way of implementing a graph is. Thanks</p>


To get maximum value of a column that contains integer, I can use the following T-SQL comand

    SELECT MAX(expression )
    FROM tables
    WHERE predicates;

Is it possible to obtain the same result with Entity Framework.

Let&#39;s say I have the following model

    public class Person
    {
      public int PersonID { get; set; }
      public int Name { get; set; }
      public int Age { get; set; }
    }

How do I get the oldest person&#39;s age?

    int maxAge = context.Persons.?

How to get max value of a column using Entity Framework?

I am trying to learn the Single Responsibility Principle (SRP) but it is being quite difficult as I am having a huge difficult to figure out when and what I should remove from one class and where I should put/organize it.

I was googling around for some materials and code examples, but most materials I found, instead of making it easier to understand, made it hard to understand.

&gt; For example if I have a list of Users and from that List I have a
&gt; class Called Control that does lots of things like Send a greeting and
&gt; goodbye message when a user comes in/out, verify weather the user
&gt; should be able to enter or not and kick him, receive user commands and messages, etc.

From the example you don&#39;t need much to understand I am already doing too much into one class but yet I am not clear enough on how to split and reorganize it afterwards.

If I understand the SRP, I would have a class for joining the channel, for the greeting and goodbye, a class for user verification, a class for reading the commands, right ?

But where and how would I use the kick for example ?

I have the verification class so I am sure I would have all sort of user verification in there including weather or not a user should be kicked.

So the kick function would be inside the channel join class and be called if the verification fails ?

For example:

    public void UserJoin(User user)
    {
        if (verify.CanJoin(user))
        {
            messages.Greeting(user);
        }
        else
        {
            this.kick(user);
        }
    }

Would appreciate if you guys could lend me a hand here with easy to understand C# materials that are online and free or by showing me how I would be splitting the quoted example and if possible some sample codes, advice, etc.

Learning Single Responsibility Principle with C#

I&#39;m able to delete, insert and update in my program and I try to do an insert by calling a created stored procedure from my database.  

This button insert I made works well.

    private void btnAdd_Click(object sender, EventArgs e)
    {
            SqlConnection con = new SqlConnection(dc.Con);
            SqlCommand cmd = new SqlCommand(&quot;Command String&quot;, con);
            
            da.InsertCommand = new SqlCommand(&quot;INSERT INTO tblContacts VALUES (@FirstName, @LastName)&quot;, con);
            da.InsertCommand.Parameters.Add(&quot;@FirstName&quot;, SqlDbType.VarChar).Value = txtFirstName.Text;
            da.InsertCommand.Parameters.Add(&quot;@LastName&quot;, SqlDbType.VarChar).Value = txtLastName.Text;

            con.Open();
            da.InsertCommand.ExecuteNonQuery();
            con.Close();

            dt.Clear();
            da.Fill(dt);
        } 

This is the start of the button that calls the procedure named `sp_Add_contact` to add a contact. The two parameters for `sp_Add_contact(@FirstName,@LastName)`. I searched on google for some good examples but found nothing interesting.

    private void button1_Click(object sender, EventArgs e)
    {
            SqlConnection con = new SqlConnection(dc.Con);
            SqlCommand cmd = new SqlCommand(&quot;Command String&quot;, con);
            cmd.CommandType = CommandType.StoredProcedure;

            ???
            
            con.Open();
            da. ???.ExecuteNonQuery();
            con.Close();

            dt.Clear();
            da.Fill(dt);
        }


Call a stored procedure with parameter in c#

I see many examples but all of them read them into byte arrays or 256 chars at a time, slowly. Why?

Is it not advisable to just convert the resulting `Stream` value into a string where I can parse it?

How to convert WebResponse.GetResponseStream return into a string?

I have a function that returns same kind of objects (query results) but with no properties or methods in common. In order to have a common type I resorted using an empty interface as a return type and &quot;implemented&quot; that on both. 

That doesn&#39;t sound right of course. I can only console myself by clinging to hope that someday those classes will have something in common and I will move that common logic to my empty interface. Yet I&#39;m not satisfied and thinking about whether I should have two different methods and conditionally call next. Would that be a better approach? 

I&#39;ve been also told that .NET Framework uses empty interfaces for tagging purposes. 

My question is: is an empty interface a strong sign of a design problem or is it widely used? 

**EDIT**: For those interested, I later found out that discriminated unions in functional languages are the perfect solution for what I was trying to achieve. C# doesn&#39;t seem friendly to that concept yet. 

**EDIT**: I wrote a [longer piece][1] about this issue, explaining the issue and the solution in detail.


  [1]: https://hackernoon.com/are-interfaces-code-smell-bd19abc266d3#.dvyk5m4ge

Are empty interfaces code smell?

I have a class (`SomeClass`) which contains a property `Name` of `string` type. And I need to store an array of that class and find its items by their names. For this purpose there are two types of collections: `KeyedCollection` and `Dictionary`. My question is: What difference between them and in such case It is better to use `KeyedCollection` and `Dictionary`? Thanks for any help in explanation.

Dictionary or KeyedCollection?

There are a lot of different ways to read and write files (*text files*, not binary) in C#. 

I just need something that is easy and uses the least amount of code, because I am going to be working with files a lot in my project. I only need something for `string` since all I need is to read and write `string`s.


Easiest way to read from and write to files

I have a website that is hosted in a different timezone than the users using the application. In addition to this, users can have a specific timezone. I was wondering how other SO users and applications approach this? The most obvious part is that inside the DB, date/times are stored in UTC. When on the server, all date/times should be dealt with in UTC. However, I see three problems that I&#39;m trying to overcome:

1. Getting the current time in UTC (solved easily with `DateTime.UtcNow`).

2. Pulling date/times from the database and displaying these to the user. There are potentially *lots* of calls to print dates on different views. I was thinking of some layer in between the view and the controllers that could solve this issue. Or having a custom extension method on `DateTime` (see below). The major down side is that at *every* location of using a datetime in a view, the extension method must be called! 

   This would also add difficulty to using something like the `JsonResult`. You could no longer easily call `Json(myEnumerable)`, it would have to be `Json(myEnumerable.Select(transformAllDates))`. Maybe AutoMapper could help in this situation?

3. Getting input from the user (Local to UTC). For example, POSTing a form with a date would require converting the date to UTC before. The first thing that comes to mind is creating a custom `ModelBinder`.

Here&#39;s the extensions that I thought of using in the views:

    public static class DateTimeExtensions
    {
        public static DateTime UtcToLocal(this DateTime source, 
            TimeZoneInfo localTimeZone)
        {
            return TimeZoneInfo.ConvertTimeFromUtc(source, localTimeZone);
        }

        public static DateTime LocalToUtc(this DateTime source, 
            TimeZoneInfo localTimeZone)
        {
            source = DateTime.SpecifyKind(source, DateTimeKind.Unspecified);
            return TimeZoneInfo.ConvertTimeToUtc(source, localTimeZone);
        }
    }

I would think that dealing with timezones would be such a common thing considering a lot of applications are now cloud-based where the server&#39;s local time could be much different than the expected time zone. 

Has this been elegantly solved before? Is there anything that I&#39;m missing? Ideas and thoughts are much appreciated.

**EDIT:** To clear some confusion I thought add some more details. The issue right now isn&#39;t *how* to store UTC times in the db, it&#39;s more about the process of going from UTC-&gt;Local and Local-&gt;UTC. As @Max Zerbini points out, it&#39;s obviously smart to put the UTC-&gt;Local code in the view, but is using the `DateTimeExtensions` really the answer? When getting input from the user, does it make sense to accept dates as the user&#39;s local time (since that&#39;s what JS would be using) and then use a `ModelBinder` to transform to UTC? The user&#39;s timezone is stored in the DB and is easily retrieved.

How to elegantly deal with timezones

There are the [`Uri.IsWellFormedUriString`](https://msdn.microsoft.com/en-us/library/system.uri.iswellformeduristring(v=vs.110).aspx) and [`Uri.TryCreate`](http://msdn.microsoft.com/en-us/library/ms131572.aspx) methods, but they seem to return `true` for file paths, etc.

How do I check whether a string is a valid (not necessarily active) HTTP URL for input validation purposes?

How to check whether a string is a valid HTTP URL?

This is a google interview question:

There are around thousand phone numbers to be stored each having 10 digits. You can assume first 5 digits of each to be same across thousand numbers. You have to perform the following operations:
a. Search if a given number exists.
b. Print all the number

What is the most efficient space saving way to do this ?

I answered hash table and later huffman coding but my interviewer said I was not going in right direction. Please help me here.

Could using a suffix trie help?



Ideally 1000 numbers storing takes 4 bytes per number so in all it would take 4000 bytes to store 1000 number. Quantitatively, I wish to reduce the storage to &lt; 4000 bytes, this is what my interviewer explained to me.


Most efficient way to store thousand telephone numbers

What is the basic algorithm for testing if a tree is symmetrical?  Because it is a binary tree, I would assume that it would be a recursive definition of sorts

The formal question is below:


A binary tree is a mirror image of itself if its left and right subtrees are identical mirror images i.e., the binary tree is symmetrical.
This is best explained with a few examples.

      1
     / \
    2   2

TRUE

       1
      / \
     2   2
      \
       3

FALSE

         1
       /   \
      2     2
     / \   / \
    4   3 3   4

TRUE

           1
         /   \
        2     2 
       / \   / \
      3   4 3   4

FALSE

           1
         /   \
        2     2
       /       \
      3         3

TRUE

In a programming language of choice, define a BTree class/C struct and an associated method to check if the tree is a mirror image. For statically typed languages, you can assume that node values are all integers.

    Class/structure definition
    BTree {
      BTree left;
      BTree right;
      int value;
    }

Assume that the root of the tree is tracked by caller and function isMirror() is invoked on it.

Also, if defining a class, make sure to provide a no-argument constructor and getter/setter methods if data elements are not publicly accessible.

Check if a binary tree is a mirror image or symmetric

I understand how to delete the root node from a max heap but is the procedure for deleting a node from the middle to remove and replace the root repeatedly until the desired node is deleted?


1. Is O(log n) the optimal complexity for this procedure?

2. Does this affect the big O complexity since other nodes must be deleted in order to delete a specific node?

How to delete in a heap data structure?

Sometimes during programming contests etc., we need a simple working implementation of min priority queue with decrease-key to implement Dijkstra algorithm etc.. I often use set&amp;lt; pair&amp;lt;key_value, ID&amp;gt; &amp;gt; and an array (mapping ID--&gt;key_value) together to achieve that. 

 - Adding an element to the set takes O(log(N)) time. To build a priority queue out of N elements, we simply add them one by one into the set. This takes O(N log(N)) time in total.

 - The element with min key_value is simply the first element of the set. Probing the smallest element takes O(1) time. Removing it takes O(log(N)) time.


 - To test whether some ID=k is in the set, we first look up its key_value=v_k in the array and then search the element (v_k, k) in the set. This takes O(log(N)) time.

 - To change the key_value of some ID=k from v_k to v_k&#39;, we first look up its key_value=v_k in the array, and then search the element (v_k, k) in the set. Next we remove that element from the set and then insert the element (v_k&#39;, k) into the set. We then update the array, too. This takes O(log(N)) time.

Although the above approach works, most textbooks usually recommend using binary heaps to implement priority queues, as the time of building the binary heaps is just O(N). I heard that there is a built-in priority queue data structure in STL of C++ that uses binary heaps. However, I&#39;m not sure how to update the key_value for that data structure.

What&#39;s the easiest and most efficient way of using min priority queue with key update in C++?

Easiest way of using min priority queue with key update in C++

Why do I keep seeing different runtime complexities for these functions on a hash table? 

On wiki, search and delete are O(n) (I thought the point of hash tables was to have constant lookup so what&#39;s the point if search is O(n)). 

In some course notes from a while ago, I see a wide range of complexities depending on certain details including one with all O(1). Why would any other implementation be used if I can get all O(1)?

If I&#39;m using standard hash tables in a language like C++ or Java, what can I expect the time complexity to be?

Hash table runtime complexity (insert, search and delete)

I am working on an implementation of Dijkstra&#39;s Algorithm to retrieve the shortest path between interconnected nodes on a network of routes. I have the implementation working. It returns all the shortest paths to all the nodes when I pass the start node into the algorithm.

My question: 
How does one go about retrieving all possible paths from Node A to, say, Node G or even all possible paths from Node A and back to Node A?


Find all paths between two graph nodes

The basic algorithm for BFS:

    set start vertex to visited
    
    load it into queue
        
    while queue not empty
        
       for each edge incident to vertex
                  
            if its not visited
                
                load into queue
                      
                mark vertex


So I would think the time complexity would be:  

    v1 + (incident edges) + v2 + (incident edges) + .... + vn + (incident edges) 


where `v` is vertex `1` to `n`


Firstly, is what I&#39;ve said correct?  Secondly, how is this `O(N + E)`, and intuition as to why would be really nice.  Thanks


Why is the time complexity of both DFS and BFS O( V + E )

I read it is ideal to represent sparse graphs by adjacency lists and dense graphs by an adjacency matrix. But I would like to understand the main difference between sparse and dense graphs. 

What is the distinction between sparse and dense graphs?

What does **`relaxation of an edge`** mean in the context of graph theory ? I came across this while studying up on Dijkstra&#39;s algorithm for single source shortest path.

Relaxation of an edge in Dijkstra&#39;s algorithm

Can somebody tell me why Dijkstra&#39;s algorithm for single source shortest path assumes that the edges must be non-negative. 

I am talking about only edges not the negative weight cycles.

Content Type	Original Author	Original Content on Stackoverflow
Question	Tae-Sung Shin	View Question on Stackoverflow
Solution 1 - C#	Lior Kogan	View Answer on Stackoverflow
Solution 2 - C#	Michael Goldshteyn	View Answer on Stackoverflow
Solution 3 - C#	TomDane	View Answer on Stackoverflow

Is there any graph data structure implemented for C#

C# Problem Overview

C# Solutions

Solution 1 - C#

Solution 2 - C#

Solution 3 - C#

NoClassDefFoundError: wrong name

GAS: Explanation of .cfi_def_cfa_offset

Attributions