moving greedy-color to rustworkx-core

[alexanderivrii]

This PR moves the greedy_color algorithm to rustworkx_core. The algorithm is exactly the same modulo some minor renaming and replacement of node_indices by node_identifiers.

The rust tests in rustworkx-core/tests/coloring.rs are adapted from python tests in rustworkx_test/graph/test_coloring.py.

---

I am wondering if there is a way to replace

let mut expected_colors = DictMap::new();
expected_colors.insert(NodeIndex::new(0), 0);
expected_colors.insert(NodeIndex::new(1), 1);
expected_colors.insert(NodeIndex::new(2), 1);

by something like DictMap::from (I was not able to make this work).

[coveralls]

Pull Request Test Coverage Report for Build 5010849131

• 32 of 32 (100.0%) changed or added relevant lines in 2 files are covered.
• 3 unchanged lines in 2 files lost coverage.
• Overall coverage decreased (-0.4%) to 96.557%

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Files with Coverage Reduction	New Missed Lines	%
src/random_graph.rs	1	99.44%
rustworkx-core/src/generators/mod.rs	2	0%

Totals
Change from base Build 4999136137:	-0.4%
Covered Lines:	14581
Relevant Lines:	15101

---

💛 - Coveralls

[mtreinish]

This LGTM, thanks for doing this. Just a couple small inline comments and questions, but then I think this is ready to merge.

[mtreinish]

Since you asked somewhere you can do this construction with something like:

Suggested change

	let mut expected_colors = DictMap::new();
	expected_colors.insert(NodeIndex::new(0), 0);
	expected_colors.insert(NodeIndex::new(1), 1);
	expected_colors.insert(NodeIndex::new(2), 1);
	let mut expected_colors: DictMap<NodeIndex, usize> = [
	(NodeIndex::new(0), 0),
	(NodeIndex::new(1), 1),
	(NodeIndex::new(2), 1),
	]
	.into_iter()
	.collect();

but manually calling insert works fine too.

[alexanderivrii]

Thanks! I like the suggested approach (and in this case we also don't need the mut keyword). I have updated the tests accordingly (and kept the original way in the docs example).

[mtreinish]

I'd be tempted to put these 3 test files under

#[cfg(test)]
mod tests {

}

in rustworkx-core/src/coloring.rs since they're isolated to just testing that module. But it doesn't matter too much I guess.

[enavarro51]

I think in our previous discussions, we want to put tests that are for only one module inside the module as you suggest. Putting new modules in tests is generally reserved for tests that are testing interactions of multiple modules.

[alexanderivrii]

Thanks! I have moved the tests to the coloring module (and I can see these running, now that I have learned to run cargo test).

[mtreinish]

Suggested change

	The function ``greedy_color``has been migrated to the ``rustworkx-core``
	crate in the ``coloring`` module. It colors a graph using a greedy
	graph coloring algorithm.
	Added a new function, ``greedy_color``, to ``rustworkx-core`` in a new
	``coloring`` module. It colors a graph using a greedy
	graph coloring algorithm.

[alexanderivrii]

Updated.

[mtreinish]

I wonder if we want to call this greedy_node_color or greedy_node_coloring just to make it a bit clear what it's doing. I don't feel super strongly this name works fine, it's just something to think about while we're adding the rust version of this function.

[alexanderivrii]

I have changed the name of the internal rust function to greedy_node_color. I don't feel strongly one way or another, but it might be slightly more clear if we are planning to add greedy_edge_color later.

[mtreinish]

This LGTM now. Just a couple small inline comments about the documentation for the new function.