57 lines
1.9 KiB
Go
57 lines
1.9 KiB
Go
// Copyright 2016-2018, Pulumi Corporation.
|
|
//
|
|
// Licensed under the Apache License, Version 2.0 (the "License");
|
|
// you may not use this file except in compliance with the License.
|
|
// You may obtain a copy of the License at
|
|
//
|
|
// http://www.apache.org/licenses/LICENSE-2.0
|
|
//
|
|
// Unless required by applicable law or agreed to in writing, software
|
|
// distributed under the License is distributed on an "AS IS" BASIS,
|
|
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
|
|
// See the License for the specific language governing permissions and
|
|
// limitations under the License.
|
|
|
|
package graph
|
|
|
|
import (
|
|
"errors"
|
|
)
|
|
|
|
// Topsort topologically sorts the graph, yielding an array of nodes that are in dependency order, using a simple
|
|
// DFS-based algorithm. The graph must be acyclic, otherwise this function will return an error.
|
|
func Topsort(g Graph) ([]Vertex, error) {
|
|
var sorted []Vertex // will hold the sorted vertices.
|
|
visiting := make(map[Vertex]bool) // temporary entries to detect cycles.
|
|
visited := make(map[Vertex]bool) // entries to avoid visiting the same node twice.
|
|
|
|
// Now enumerate the roots, topologically sorting their dependencies.
|
|
roots := g.Roots()
|
|
for _, r := range roots {
|
|
if err := topvisit(r.To(), &sorted, visiting, visited); err != nil {
|
|
return sorted, err
|
|
}
|
|
}
|
|
return sorted, nil
|
|
}
|
|
|
|
func topvisit(n Vertex, sorted *[]Vertex, visiting map[Vertex]bool, visited map[Vertex]bool) error {
|
|
if visiting[n] {
|
|
// This is not a DAG! Stop sorting right away, and issue an error.
|
|
// IDEA: return diagnostic information about why this isn't a DAG (e.g., full cycle path).
|
|
return errors.New("Graph is not a DAG")
|
|
}
|
|
if !visited[n] {
|
|
visiting[n] = true
|
|
for _, m := range n.Outs() {
|
|
if err := topvisit(m.To(), sorted, visiting, visited); err != nil {
|
|
return err
|
|
}
|
|
}
|
|
visited[n] = true
|
|
visiting[n] = false
|
|
*sorted = append(*sorted, n)
|
|
}
|
|
return nil
|
|
}
|