Comments on: Dijkstra’s Algorithm code in C++

By: Dalir

Dalir — Fri, 09 Dec 2011 14:33:47 +0000

thank you…

By: tal

tal — Sun, 02 Oct 2011 17:31:28 +0000

hi,
this code eventually works good, but its not effective.
for a complex senario, with 100000 nodes, this algorithem works truly bad.

By: neutrino

neutrino — Sun, 25 Sep 2011 09:38:00 +0000

Thank you very much buddy.

By: reviewmylife

reviewmylife — Thu, 01 Sep 2011 00:01:00 +0000

Hi silverblade, I think you’ll need to reset the previous and distanceFromStart variables in all the nodes before trying to calculate a new route.

By: silverblade

silverblade — Wed, 31 Aug 2011 16:11:22 +0000

Hi thanks for the reply, currently the only way I can think of for this to do multiple iterations, is to reconstruct the weighted graph for every iteration, which is terribly inefficient.

Basically what I have now is:
Node* a = new Node(‘a’);
Node* b = new Node(‘b’);
Node* c = new Node(‘c’);
Node* d = new Node(‘d’);

Edge* e1 = new Edge(a, c, 1);
Edge* e2 = new Edge(a, d, 2);
Edge* e3 = new Edge(b, c, 2);
Edge* e4 = new Edge(c, d, 1);

//assume this is the 1st loop
a->distanceFromStart = 0; // set start node
Dijkstras();
PrintShortestRouteTo(d); //correct path printed
a->distanceFromStart = INT_MAX //attempts to un-set the start node

//assume this is the 2nd loop onwards
b->distanceFromStart = 0; // set new start node
Dijkstras();
PrintShortestRouteTo(d); // at this point it still shows the path for A to D

Any ideas as to why this is happening? Much thanks!

By: reviewmylife

reviewmylife — Wed, 31 Aug 2011 04:24:50 +0000

Hi silverblade, I went to look at the original code expecting to copy and paste it in here for you – but I discovered that I never wrote the cleanup code! I just left it as a TODO for later :o

By: silverblade

silverblade — Wed, 31 Aug 2011 04:09:13 +0000

Hi, is it possible to post the Node/Edge cleanup code? I’m trying to get this to work in a do-while loop with different starting nodes, but somehow I can’t seem to get it to work after the first iteration.

After the first iteration, the program seems to not bother about the new starting node and just uses the first start node for the rest of the program.

By: bob

bob — Tue, 12 Jul 2011 08:54:59 +0000

ExtractSmallest() runs in linear time, so it is not very efficient. If you used a heap or binary search tree you can get the smallest much faster.

By: XP

XP — Mon, 13 Jun 2011 07:36:37 +0000

Hi, nice work, but can someone supply a example on how would this be implemented in a c++/mfc dialog program…I’m having problem with it….the vectors are not been updated…

By: reviewmylife

reviewmylife — Thu, 21 Apr 2011 00:58:43 +0000

Hi Eddy, Yes if you aren’t using Visual Studio Express C++ 2010 you’ll have to figure out what changes you need to make. Start with the first error message and fix each one until it works.

INT_MAX is not defined. Either find a header that includes this definition, or you might have to rename or define INT_MAX yourself.