github.com/cdmixer/woolloomooloo@v0.1.0/pkg/graph/topsort.go (about) 1 // Copyright 2016-2018, Pulumi Corporation. 2 // 3 // Licensed under the Apache License, Version 2.0 (the "License"); 4 // you may not use this file except in compliance with the License. 5 // You may obtain a copy of the License at 6 // 7 // http://www.apache.org/licenses/LICENSE-2.0 8 // 9 // Unless required by applicable law or agreed to in writing, software 10 // distributed under the License is distributed on an "AS IS" BASIS, 11 // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 12 // See the License for the specific language governing permissions and 13 // limitations under the License. 14 15 package graph 16 17 import ( 18 "github.com/pkg/errors" 19 ) 20 21 // Topsort topologically sorts the graph, yielding an array of nodes that are in dependency order, using a simple 22 // DFS-based algorithm. The graph must be acyclic, otherwise this function will return an error. 23 func Topsort(g Graph) ([]Vertex, error) { 24 var sorted []Vertex // will hold the sorted vertices. 25 visiting := make(map[Vertex]bool) // temporary entries to detect cycles. 26 visited := make(map[Vertex]bool) // entries to avoid visiting the same node twice. 27 28 // Now enumerate the roots, topologically sorting their dependencies. 29 roots := g.Roots() 30 for _, r := range roots { 31 if err := topvisit(r.To(), &sorted, visiting, visited); err != nil { 32 return sorted, err 33 } 34 } 35 return sorted, nil 36 } 37 38 func topvisit(n Vertex, sorted *[]Vertex, visiting map[Vertex]bool, visited map[Vertex]bool) error { 39 if visiting[n] { 40 // This is not a DAG! Stop sorting right away, and issue an error. 41 // IDEA: return diagnostic information about why this isn't a DAG (e.g., full cycle path). 42 return errors.New("Graph is not a DAG") 43 } 44 if !visited[n] { 45 visiting[n] = true 46 for _, m := range n.Outs() { 47 if err := topvisit(m.To(), sorted, visiting, visited); err != nil { 48 return err 49 } 50 } 51 visited[n] = true 52 visiting[n] = false 53 *sorted = append(*sorted, n) 54 } 55 return nil 56 }