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Apologies for the shouting but this is important.
When answering a question please:
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Insults, slap-downs and sarcasm aren't welcome. Let's work to help developers, not make them feel stupid.
cheers,
Chris Maunder
The Code Project Co-founder
Microsoft C++ MVP
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For those new to message boards please try to follow a few simple rules when posting your question.- Choose the correct forum for your message. Posting a VB.NET question in the C++ forum will end in tears.
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cheers,
Chris Maunder
The Code Project Co-founder
Microsoft C++ MVP
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We got an assignment where we have to find the shortest route between S and G and use the bfs, dfs, a* & dijkstra algorithms.
I'm not sure I did the steps correctly, I'd love to know if I made a mistake and where.
For example in dijksra, when I got to point T I didn't know exactly what to do,
if it was possible to end the search and go straight to G, or as I did - go to D and then to G.
Regarding the *A, I'm not at all sure that I did it right.. at least the table of steps..
I would appreciate your help.
Pdf:
Ex0[^]
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Help with what? You showed no code, and nobody in their right mind is going to click on your link.
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its just a pdf file, scan it if you want to.
I'm new here and didn't find a way to upload img
Smallpdf.com[^]
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Still on a clicking a link. I told you the code shows up in a post here, or nothing gets answered.
Posting images is not allowed, for obvious abuse reasons.
What on earth is so difficult about copying RELEVANT code from your IDE into the little post window and wrapping it in PRE tags?
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It's not a code, it's a graph where we have to find the shortest route from point to point using an algorithm.
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Then that's a question for your teacher.
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You're, in effect, asking us to confirm the validity of "your steps". That would be the job of whoever gave you the "assignment". As it stands, that would require too much effort on our part ("read my pdf").
"Before entering on an understanding, I have meditated for a long time, and have foreseen what might happen. It is not genius which reveals to me suddenly, secretly, what I have to say or to do in a circumstance unexpected by other people; it is reflection, it is meditation." - Napoleon I
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I suspect strongly that there are multiple sites which specialize in discussions of math. Your question is probably better asked there.
You might want to phrase it more carefully with more detail. (But that might just be that it so long that I have looked at stuff like that that I cannot judge the question.)
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So we know the node S and we know the node G, we've got a bunch of links leading out of S, and we've a bunch of links leading to G. And armed with that information we want to find the shortest path.
So one way is exhaustive enumeration of the entire graph starting from S, and following links from. And the other way is exhaustive enumeration of the entire graph starting at G, and following links to. And both of those will work, but require enumeration of the entire graph, ad we want to be a little clever.
So what do we do? What we do is push out little bubbles from S and G, one link away, two links away, and so on. And we keep a list of nodes for S and G in the bubbles. And eventually a node in the S bubble turns out to be a node in the G bubble, or vice versa, and you've found a path, and the shortest path for most graphs.
And then, knowing a bit about the graph topology, we can refine things a bit to speed up the normal case search. But get the two bubbles system working first, and then come back, and we'll discuss how to refine.
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I'd like to have non C# metadata about some of my classes stored with those classes.
I tried creating static virtual methods that would return the metadata, but alas, C# doesn't support static virtual methods.
So it got me thinking...What's the best way to store metadata about classes inside those classes so that you can retrieve it from an instance or from a static method?
Or is there another better way to store metadata about the classes?
SOLUTION: I'll just create virtual instance methods. But I'd still like to hear your thoughts on the matter.
SECOND SOLUTION: Due to Gerry's suggestion, I am now using Attributes for this purpose. It's working out better than instance methods would have.
The difficult we do right away...
...the impossible takes slightly longer.
modified 31-Dec-23 11:24am.
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I was going to suggest "attributes" ... or is that "C# metadata"? ... which you don't want.
Extending Metadata Using Attributes - .NET | Microsoft Learn
"Before entering on an understanding, I have meditated for a long time, and have foreseen what might happen. It is not genius which reveals to me suddenly, secretly, what I have to say or to do in a circumstance unexpected by other people; it is reflection, it is meditation." - Napoleon I
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I need to store information that one cannot get from .net reflection. That's all I meant by non C#.
But I think that attributes might be what I'm looking for.
Thanks for the idea!
The difficult we do right away...
...the impossible takes slightly longer.
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My program contains a List<T> object that is extremely critical to the program's function.
In normal use, it will be accessed by many ( >10 ) worker threads.
I don't need to synchronize worker thread access, because the workers never write to the collection, it's read-only to the worker threads.
However, I want to be able to make changes to the list in a single, central class. And I'd like to be able to temporarily shut off worker-thread access to the list while changes are being made by a thread in the central class.
I'd like not to require the worker threads to acquire a mutex every time they need access due to performance reasons.
So, is there a pattern by which I can make access to the List<T> very fast for the worker threads, but still be able to shut off worker access while the list is being updated by the central class?
The difficult we do right away...
...the impossible takes slightly longer.
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Yes! That should do the job. I didn't know that they made a primitive exactly for this use case.
Thanks!
The difficult we do right away...
...the impossible takes slightly longer.
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Richard Andrew x64 wrote: And I'd like to be able to temporarily shut off worker-thread access
If you remove that requirement you can implement a solution with no locks of any sort.
Basic idea...
For the workers
static ListX realList = ...;
DoWork()
{
ListX temp = realList;
}
For the the controller
ManageListX()
{
ListX newList = new ListX();
realList = newList;
}
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Thanks, that's a great idea.
I thought of that, but I decided against it because it might lead to some threads seeing the new version of the list while other threads are still working with data from the old version of the list. Also, the worker threads enumerate the list, so that would lead to exceptions caused by changing the list out from under them.
The difficult we do right away...
...the impossible takes slightly longer.
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If you take a local copy (often a good idea anyway) you can avoid the second problem. Then a worker would keep hold of the same list until it's ready for the list to change. Doesn't do anything about the first problem.
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When you refer to a local copy of the list, do you mean a copy local to each worker thread, or local to the worker module, (all worker threads can access)?
If you mean local to each worker thread, then that becomes expensive creating a deep copy of the list every time a worker needs to reference it.
Do I misunderstand?
The difficult we do right away...
...the impossible takes slightly longer.
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A shallow copy does the trick. jschell doesn't want to call this a shallow copy, whatever. What I meant, and what the whole thread has always been about, is assigning the list to a local variable, and never editing its contents, only replacing the whole thing. The list which a reader is iterating over does not change since it has an .. even shallower f***ing copy, whatever the f*** you want to call it. Copy of the pointer. They can update that when they're ready for it to change.
The list is never modified anyway, only replaced. At least that was the premise of this sub-thread stared by jschell
modified 29-Dec-23 11:32am.
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Shallow copy of the list?
No rebuild the entire list brand new.
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Threads take a copy of the reference to the list. Making a new list builds it brand new. There is no reason for threads to make a deep copy since the list, once made, never changes (only replaced as a whole).
E: why are you making me re-explain your own idea back to you anyway? You know how this works, you suggested it.
modified 29-Dec-23 11:19am.
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