├── .gitignore ├── LICENSE ├── README.md ├── go.mod ├── topsort.go └── topsort_test.go /.gitignore: -------------------------------------------------------------------------------- 1 | # Compiled Object files, Static and Dynamic libs (Shared Objects) 2 | *.o 3 | *.a 4 | *.so 5 | 6 | # Folders 7 | _obj 8 | _test 9 | 10 | # Architecture specific extensions/prefixes 11 | *.[568vq] 12 | [568vq].out 13 | 14 | *.cgo1.go 15 | *.cgo2.c 16 | _cgo_defun.c 17 | _cgo_gotypes.go 18 | _cgo_export.* 19 | 20 | _testmain.go 21 | 22 | *.exe 23 | -------------------------------------------------------------------------------- /LICENSE: -------------------------------------------------------------------------------- 1 | Apache License 2 | Version 2.0, January 2004 3 | http://www.apache.org/licenses/ 4 | 5 | TERMS AND CONDITIONS FOR USE, REPRODUCTION, AND DISTRIBUTION 6 | 7 | 1. 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We also 175 | recommend that a file or class name and description of purpose be included on 176 | the same "printed page" as the copyright notice for easier identification within 177 | third-party archives. 178 | 179 | Copyright [yyyy] [name of copyright owner] 180 | 181 | Licensed under the Apache License, Version 2.0 (the "License"); 182 | you may not use this file except in compliance with the License. 183 | You may obtain a copy of the License at 184 | 185 | http://www.apache.org/licenses/LICENSE-2.0 186 | 187 | Unless required by applicable law or agreed to in writing, software 188 | distributed under the License is distributed on an "AS IS" BASIS, 189 | WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 190 | See the License for the specific language governing permissions and 191 | limitations under the License. 192 | -------------------------------------------------------------------------------- /README.md: -------------------------------------------------------------------------------- 1 | topsort 2 | ======= 3 | 4 | Topological Sorting for Golang 5 | 6 | Topological sorting algorithms are especially useful for dependency calculation, and so this particular implementation is mainly intended for this purpose. As a result, the direction of edges and the order of the results may seem reversed compared to other implementations of topological sorting. 7 | 8 | For example, if: 9 | 10 | * A depends on B 11 | * B depends on C 12 | 13 | The graph is represented as: 14 | 15 | ``` 16 | A -> B -> C 17 | ``` 18 | 19 | Where `->` represents a directed edge from one node to another. 20 | 21 | The topological ordering of dependencies results in: 22 | 23 | ``` 24 | [C, B, A] 25 | ``` 26 | 27 | The code for this example would look something like: 28 | 29 | ```go 30 | // Initialize the graph. 31 | graph := topsort.NewGraph[string]() 32 | 33 | // Add edges. 34 | graph.AddEdge("A", "B") 35 | graph.AddEdge("B", "C") 36 | 37 | // Topologically sort node A. 38 | graph.TopSort("A") // => [C, B, A] 39 | ``` 40 | -------------------------------------------------------------------------------- /go.mod: -------------------------------------------------------------------------------- 1 | module github.com/stevenle/topsort/v2 2 | 3 | go 1.18 4 | -------------------------------------------------------------------------------- /topsort.go: -------------------------------------------------------------------------------- 1 | // Copyright 2013 Steven Le. All rights reserved. 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 topsort 16 | 17 | import ( 18 | "fmt" 19 | "strings" 20 | ) 21 | 22 | type Graph[Key comparable] struct { 23 | nodes map[Key]nodeimpl[Key] 24 | } 25 | 26 | func NewGraph[Key comparable]() *Graph[Key] { 27 | return &Graph[Key]{ 28 | nodes: make(map[Key]nodeimpl[Key]), 29 | } 30 | } 31 | 32 | func (g *Graph[Key]) AddNode(key Key) { 33 | if !g.ContainsNode(key) { 34 | g.nodes[key] = make(nodeimpl[Key]) 35 | } 36 | } 37 | 38 | func (g *Graph[Key]) getOrAddNode(node Key) nodeimpl[Key] { 39 | n, ok := g.nodes[node] 40 | if !ok { 41 | n = make(nodeimpl[Key]) 42 | g.nodes[node] = n 43 | } 44 | return n 45 | } 46 | 47 | func (g *Graph[Key]) AddEdge(from Key, to Key) error { 48 | f := g.getOrAddNode(from) 49 | g.AddNode(to) 50 | f.addEdge(to) 51 | return nil 52 | } 53 | 54 | func (g *Graph[Key]) ContainsNode(key Key) bool { 55 | _, ok := g.nodes[key] 56 | return ok 57 | } 58 | 59 | func (g *Graph[Key]) TopSort(key Key) ([]Key, error) { 60 | results := newOrderedSet[Key]() 61 | err := g.visit(key, results, nil) 62 | if err != nil { 63 | return nil, err 64 | } 65 | return results.items, nil 66 | } 67 | 68 | func (g *Graph[Key]) visit(key Key, results *orderedset[Key], visited *orderedset[Key]) error { 69 | if visited == nil { 70 | visited = newOrderedSet[Key]() 71 | } 72 | 73 | added := visited.add(key) 74 | if !added { 75 | index := visited.index(key) 76 | cycle := append(visited.items[index:], key) 77 | strs := make([]string, len(cycle)) 78 | for i, k := range cycle { 79 | strs[i] = fmt.Sprintf("%v", k) 80 | } 81 | return fmt.Errorf("Cycle error: %s", strings.Join(strs, " -> ")) 82 | } 83 | 84 | n := g.nodes[key] 85 | for _, edge := range n.edges() { 86 | err := g.visit(edge, results, visited.copy()) 87 | if err != nil { 88 | return err 89 | } 90 | } 91 | 92 | results.add(key) 93 | return nil 94 | } 95 | 96 | type nodeimpl[Key comparable] map[Key]bool 97 | 98 | func (n nodeimpl[Key]) addEdge(key Key) { 99 | n[key] = true 100 | } 101 | 102 | func (n nodeimpl[Key]) edges() []Key { 103 | var keys []Key 104 | for k := range n { 105 | keys = append(keys, k) 106 | } 107 | return keys 108 | } 109 | 110 | type orderedset[Key comparable] struct { 111 | indexes map[Key]int 112 | items []Key 113 | length int 114 | } 115 | 116 | func newOrderedSet[Key comparable]() *orderedset[Key] { 117 | return &orderedset[Key]{ 118 | indexes: make(map[Key]int), 119 | length: 0, 120 | } 121 | } 122 | 123 | func (s *orderedset[Key]) add(item Key) bool { 124 | _, ok := s.indexes[item] 125 | if !ok { 126 | s.indexes[item] = s.length 127 | s.items = append(s.items, item) 128 | s.length++ 129 | } 130 | return !ok 131 | } 132 | 133 | func (s *orderedset[Key]) copy() *orderedset[Key] { 134 | clone := newOrderedSet[Key]() 135 | for _, item := range s.items { 136 | clone.add(item) 137 | } 138 | return clone 139 | } 140 | 141 | func (s *orderedset[Key]) index(item Key) int { 142 | index, ok := s.indexes[item] 143 | if ok { 144 | return index 145 | } 146 | return -1 147 | } 148 | -------------------------------------------------------------------------------- /topsort_test.go: -------------------------------------------------------------------------------- 1 | // Copyright 2013 Steven Le. All rights reserved. 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 topsort 16 | 17 | import ( 18 | "strings" 19 | "testing" 20 | ) 21 | 22 | func TestTopSort(t *testing.T) { 23 | graph := initGraph() 24 | 25 | // a -> b -> c 26 | graph.AddEdge("a", "b") 27 | graph.AddEdge("b", "c") 28 | 29 | results, err := graph.TopSort("a") 30 | if err != nil { 31 | t.Error(err) 32 | return 33 | } 34 | if results[0] != "c" || results[1] != "b" || results[2] != "a" { 35 | t.Errorf("Wrong sort order: %v", results) 36 | } 37 | } 38 | 39 | func TestTopSort2(t *testing.T) { 40 | graph := initGraph() 41 | 42 | // a -> c 43 | // a -> b 44 | // b -> c 45 | graph.AddEdge("a", "c") 46 | graph.AddEdge("a", "b") 47 | graph.AddEdge("b", "c") 48 | 49 | results, err := graph.TopSort("a") 50 | if err != nil { 51 | t.Error(err) 52 | return 53 | } 54 | if results[0] != "c" || results[1] != "b" || results[2] != "a" { 55 | t.Errorf("Wrong sort order: %v", results) 56 | } 57 | } 58 | 59 | func TestTopSort3(t *testing.T) { 60 | graph := initGraph() 61 | 62 | // a -> b 63 | // a -> d 64 | // d -> c 65 | // c -> b 66 | graph.AddEdge("a", "b") 67 | graph.AddEdge("a", "d") 68 | graph.AddEdge("d", "c") 69 | graph.AddEdge("c", "b") 70 | 71 | results, err := graph.TopSort("a") 72 | if err != nil { 73 | t.Error(err) 74 | return 75 | } 76 | if len(results) != 4 { 77 | t.Errorf("Wrong number of results: %v", results) 78 | return 79 | } 80 | expected := [4]string{"b", "c", "d", "a"} 81 | for i := 0; i < 4; i++ { 82 | if results[i] != expected[i] { 83 | t.Errorf("Wrong sort order: %v", results) 84 | break 85 | } 86 | } 87 | } 88 | 89 | func TestTopSortCycleError(t *testing.T) { 90 | graph := initGraph() 91 | 92 | // a -> b 93 | // b -> a 94 | graph.AddEdge("a", "b") 95 | graph.AddEdge("b", "a") 96 | 97 | _, err := graph.TopSort("a") 98 | if err == nil { 99 | t.Errorf("Expected cycle error") 100 | return 101 | } 102 | if !strings.Contains(err.Error(), "a -> b -> a") { 103 | t.Errorf("Error doesn't print cycle: %q", err) 104 | } 105 | } 106 | 107 | func TestTopSortCycleError2(t *testing.T) { 108 | graph := initGraph() 109 | 110 | // a -> b 111 | // b -> c 112 | // c -> a 113 | graph.AddEdge("a", "b") 114 | graph.AddEdge("b", "c") 115 | graph.AddEdge("c", "a") 116 | 117 | _, err := graph.TopSort("a") 118 | if err == nil { 119 | t.Errorf("Expected cycle error") 120 | return 121 | } 122 | if !strings.Contains(err.Error(), "a -> b -> c -> a") { 123 | t.Errorf("Error doesn't print cycle: %q", err) 124 | } 125 | } 126 | 127 | func TestTopSortCycleError3(t *testing.T) { 128 | graph := initGraph() 129 | 130 | // a -> b 131 | // b -> c 132 | // c -> b 133 | graph.AddEdge("a", "b") 134 | graph.AddEdge("b", "c") 135 | graph.AddEdge("c", "b") 136 | 137 | _, err := graph.TopSort("a") 138 | if err == nil { 139 | t.Errorf("Expected cycle error") 140 | return 141 | } 142 | if !strings.Contains(err.Error(), "b -> c -> b") { 143 | t.Errorf("Error doesn't print cycle: %q", err) 144 | } 145 | } 146 | 147 | func initGraph() *Graph[string] { 148 | graph := NewGraph[string]() 149 | return graph 150 | } 151 | --------------------------------------------------------------------------------