This weekend will feature two Algorithms Live! episodes. This will hopefully make up for last week's technical difficulties.
Episode 7 will take place tomorrow and cover Steiner Trees. I'll be covering the solution idea to Ticket to Ride from NWERC 2006. You can find the problem here: http://www.csc.kth.se/contest/nwerc/2006/problems/nwerc06.pdf
SPOJ also has the problem if you would like to try it: http://www.spoj.com/problems/TICKET/
I'll be discussing two approaches for solving Steiner Tree problems for different bounds and some optimizations for making the approaches faster. I'll also live code the solution to Ticket to Ride.
Here is the info for the new Episode 7: (time, stream, channel)
On Sunday, Makoto Soejima will join Algorithms Live! to make up last week's episode. This episode will now be Episode 8. He will answer many of your posted questions, discuss AtCoder, and discuss the problem "90 and 270". You can find more information about the episode in the previous post.
Here is the info for Episode 8: (time, stream, channel)
See you live!
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ReplyDeleteSecond, I have a question regarding finding the actual steiner trees themselves. I have a problem where i'd like to find all steiner trees.
I used the dynamic programming in your video, but I noticed that if I have two solutions with the same minimum cost, then it seems impossible for me to know which nodes are part of which steiner tree.
What I did to find all steiner tree was:
1. delete nodes whose minimum cost are NOT the global minimum
2. find all pairs shortest path for the remaining nodes
3. loop over all nodes and connect them to each terminal using the shortest paths
4. select the resulting trees whose weight is minimal.
This procedure alone (i.e. running it on all nodes) is, I believe, an approximation to steiner tree, not guaranteed to find the optimal solution. However if I run it on only the nodes that are part of some optimal solution (as given by the DP), I feel that it may give be the right answer, but I am not sure. Thoughts?
Thanks!
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