32 lines
1.1 KiB
Python
32 lines
1.1 KiB
Python
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def topological_sort_as_sets(dependency_graph):
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"""Variation of Kahn's algorithm (1962) that returns sets.
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Takes a dependency graph as a dictionary of node => dependencies.
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Yields sets of items in topological order, where the first set contains
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all nodes without dependencies, and each following set contains all
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nodes that depend on the nodes in the previously yielded sets.
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"""
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todo = dependency_graph.copy()
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while todo:
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current = {node for node, deps in todo.items() if len(deps) == 0}
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if not current:
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raise ValueError('Cyclic dependency in graph: {}'.format(
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', '.join(repr(x) for x in todo.items())))
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yield current
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# remove current from todo's nodes & dependencies
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todo = {node: (dependencies - current) for node, dependencies in
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todo.items() if node not in current}
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def stable_topological_sort(l, dependency_graph):
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result = []
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for layer in topological_sort_as_sets(dependency_graph):
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for node in l:
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if node in layer:
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result.append(node)
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return result
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