CODEWITHSUNDEEP
breadth-first-searchshortest-pathdijkstra
samabu
samabu

Reputation: 183

Can I use Breadth-First-Search on weighted graphs if I modify it?

I am having a discussion with a friend if the following will work:

We recently learned in a lecture about Breadth-First-Search. I know that it is a special case of Dijkstra where each edge weight is set to one. Assume now we are given a graph where the edges have integer weights of more than one. Then I would modify this graph by introducing additional vertices and connecting them by edges with weight one, e.g. assume we have an edge of weight 3 connecting the vertices u and v, then I would introduce dummy-vertices d1, d2, remove the edge connecting u and v and instead add edges {u, d1}, {d1, d2}, {d2,v} of weight one.

If I modify my whole graph this way and then apply breadth-first search starting from one of the original vertices, wouldn't this work as well?

Thank you very much in advance!

Upvotes: 2

Views: 688

Answers (1)

BlueRaja - Danny Pflughoeft
BlueRaja - Danny Pflughoeft

Reputation: 86023

Since BFS is guaranteed to return an optimal path on unweighted graphs, and you've created the unweighted equivalent of your original graph, you'll be guaranteed to get the shortest path.

What you lose by doing this over Dijkstra's algorithm is runtime optimality. Now the runtime of your algorithm is dependent on the edge weights, whereas Dijkstra's is only dependent on the number of edges.

This sort of thought experiment is a great way to understand how Dijkstra's algorithm works (eg. how would you modify your algorithm to not require creating a new graph? Or not take 100 steps for an edge with weight 100?). In fact this is probably how Dijkstra discovered the algorithm to begin with.

Upvotes: 1

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