45 lines
1.4 KiB
Go
45 lines
1.4 KiB
Go
// Copyright 2016-2017, Pulumi Corporation. All rights reserved.
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package graph
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import (
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"github.com/pkg/errors"
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)
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// Topsort topologically sorts the graph, yielding an array of nodes that are in dependency order, using a simple
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// DFS-based algorithm. The graph must be acyclic, otherwise this function will return an error.
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func Topsort(g Graph) ([]Vertex, error) {
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var sorted []Vertex // will hold the sorted vertices.
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visiting := make(map[Vertex]bool) // temporary entries to detect cycles.
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visited := make(map[Vertex]bool) // entries to avoid visiting the same node twice.
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// Now enumerate the roots, topologically sorting their dependencies.
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roots := g.Roots()
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for _, r := range roots {
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if err := topvisit(r.To(), &sorted, visiting, visited); err != nil {
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return sorted, err
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}
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}
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return sorted, nil
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}
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func topvisit(n Vertex, sorted *[]Vertex, visiting map[Vertex]bool, visited map[Vertex]bool) error {
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if visiting[n] {
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// This is not a DAG! Stop sorting right away, and issue an error.
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// IDEA: return diagnostic information about why this isn't a DAG (e.g., full cycle path).
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return errors.New("Graph is not a DAG")
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}
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if !visited[n] {
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visiting[n] = true
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for _, m := range n.Outs() {
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if err := topvisit(m.To(), sorted, visiting, visited); err != nil {
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return err
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}
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}
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visited[n] = true
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visiting[n] = false
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*sorted = append(*sorted, n)
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}
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return nil
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}
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