Add a utility for finding minimal topological sorts #6884
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Reuse the code implementing Kahn's topological sort algorithm with a new configuration that uses a min-heap to always choose the best available element. Also add wrapper utilities that can find topological sorts of graphs with arbitrary element types, not just indices.
kripken
approved these changes
Aug 29, 2024
src/support/topological_orders.h
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| @@ -36,7 +38,8 @@ struct TopologicalOrders { | |||
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| // Takes an adjacency list, where the list for each vertex is a sorted list of | |||
| // the indices of its children, which will appear after it in the order. | |||
| TopologicalOrders(const std::vector<std::vector<size_t>>& graph); | |||
| TopologicalOrders(const std::vector<std::vector<size_t>>& graph) | |||
| : TopologicalOrders(graph, false) {} | |||
| const std::vector<size_t>& operator*() const { | ||
| return TopologicalOrders::operator*(); | ||
| } | ||
| }; |
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This constructor is identical to the parent, and this operator doesn't seem to modify anything either - I am sure I'm missing something?
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Nope, this is providing a small subset of the functionality of the superclass, packaged under a different name that is more appropriate for the common case of needing just one topological sort.
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Ah, thanks... I was missing the word "private" on line 108. Makes sense now.
| Graph graph(3); | ||
| graph[2].push_back(1); | ||
| std::vector<size_t> expected{0, 2, 1}; | ||
| EXPECT_EQ(*MinTopologicalSort(graph), expected); |
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Maybe add comments to these, e.g. for this one IIUC the point is to show that 2 is before 1, and the unconstrained 0 is smaller so it appears before them both.
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Reuse the code implementing Kahn's topological sort algorithm with a new
configuration that uses a min-heap to always choose the best available
element.
Also add wrapper utilities that can find topological sorts of graphs
with arbitrary element types, not just indices.