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38 lines
751 B
Ruby
38 lines
751 B
Ruby
# Topological ordering of a directed graph is a linear ordering of
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# its vertices such that for every directed edge uv from vertex u to vertex v,
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# u comes before v in the ordering.
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class Dag
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attr_accessor :nodes
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def topological_sort
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# Tarjan's algorithm
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@sorted_nodes = []
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@unmarked_nodes = @nodes.dup
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visit(@unmarked_nodes.sample) while @unmarked_nodes.count > 0
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@sorted_nodes
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end
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def visit(node)
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# Depth First Search
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unless @unmarked_nodes.include? node
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node.neighbors.each { |neighbor| visit(neighbor) }
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@unmarked_nodes.delete(node)
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@sorted_nodes.unshift node
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end
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end
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end
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class Node
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attr_accessor :neighbors
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def initialize(neighbors)
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@neighbors = neighbors
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end
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end
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