Implement Bellman–Ford

[dionyziz]

The current implementation only includes a way to find single source shortest paths in graphs with positive edges using Dijkstra. It would be useful to have an implementation where this restriction is not necessary. This would require the Bellman–Ford algorithm.

Ideally, I would like to see three functions: .dijkstra and .bellmanFord and simply .shortestPaths which chooses the appropriate underlying algorithm among the previous two. This would require keeping track of whether there are any negative edges (by counting them).

[mstou]

Given that checking for negative edges requires Θ(E) ( maybe until edges are handled diffrently by the library #90 ) , is the .shortestPaths function still wanted? Should I include it in #88 ?

[dionyziz]

All shortestPath implementations we have are Ω(E) so the asymptotic complexity is not harmed by including an initial check for negative edges. Hence I think it makes sense even if #90 is not implemented.

[mstou]

Yes, you're right, i'll add it in #88