Sunday, October 02, 2005

Modified Dijkstra's algorithm in Python

Algorithm: perform a breadth-first search, always expand the vertex with the smallest cost, and don't remove duplicate vertices in the cost-priority-queue.

This algorithm turns out to be nearly equivalent to Dijkstra's algorithm. For n vertices and m edges, it requires O(n+m) space, O(m*log(m)) time, and always finds the shortest path.

The strategy of not removing duplicate vertices is particularly helpful in Python, where the builtin priority queue class doesn't support the DECREASE-KEY operation. See my comment at David Eppstein's recipe (the comment is public domain).


Anonymous said...

That, sir, is one of the most elegant Dijkstra I've ever seen. Thanks for sharing.

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Sildenafil Citrate said...

I am started to learn Python stuff two days ago and I don't really know that hang of it yet, but with your posts I am learning the basics, thanks!

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