Make graph.add_edge run in O(1) instead of O(degree(V))

[dkorduban]

Right now graph.add_edge runs in O(degree(V)) because node_neighbors is a list and v not in self.node_neighbors[u] runs in O(len(self.node_neighbors)). This leads to O(EV) creation time for dense graphs. Another worst case is a star — a graph where a single vertex is connected to each of other vertices, which will be constructed in O(V^2) having just O(V) edges & vertices.

This pull request fixes v not in self.node_neighbors[u] running time by making node_neighbors a set, which guarantees O(1) __contains__ check. neighbors still cast it to list for immutability & backward compatibility.

[coveralls]

Pull Request Test Coverage Report for Build 19

• 4 of 4 (100.0%) changed or added relevant lines in 1 file are covered.
• 3 unchanged lines in 1 file lost coverage.
• Overall coverage decreased (-0.2%) to 93.654%

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Files with Coverage Reduction	New Missed Lines	%
core/pygraph/algorithms/minmax.py	3	95.24%

Totals
Change from base Build 17:	-0.2%
Covered Lines:	1225
Relevant Lines:	1308

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💛 - Coveralls

[goldragoon]

@agroszer
Why don't you review this pull request?
I think it's quite nice.

[agroszer]

yeah, did not notice the PR...

@dkorduban would be nice to get coverage back

[dkorduban]

The coverage issue is unrelated to the changes (the same happens in #1 ). I can fix it in a different pull request though.

[agroszer]

had that feeling....

thank you