Improving The Floyd-Warshall All Pairs Shortest Paths Algorithm
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The Floyd-Warshall algorithm is the most popular algorithm for determining the shortest paths between all pairs in a graph. It is very a simple and an elegant algorithm. However, if the graph does not contain any negative weighted edge, using Dijkstra's shortest path algorithm for every vertex as a source vertex to produce all pairs shortest paths of the graph works much better than the Floyd-Warshall algorithm for sparse graphs. Also, for the graphs with negative weighted edges, with no negative cycle, Johnson's algorithm still performs significantly better than the Floyd-Warshall algorithm for sparse graphs. Johnson's algorithm transforms the graph into a non-negative one by using the Bellman-Ford algorithm, then, applies the Dijkstra's algorithm. Thus, in general the Floyd-Warshall algorithm becomes very inefficient especially for sparse graphs. In this paper, we show a simple improvement on the Floyd-Warshall algorithm that will increases its performance especially for the sparse graphs, so it can be used instead of more complicated alternatives.
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