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// Copyright 2022 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
package dag
// Transpose reverses all edges in g.
func (g *Graph) Transpose() {
old := g.edges
g.edges = make(map[string]map[string]bool)
for _, n := range g.Nodes {
g.edges[n] = make(map[string]bool)
}
for from, tos := range old {
for to := range tos {
g.edges[to][from] = true
}
}
}
// Topo returns a topological sort of g. This function is deterministic.
func (g *Graph) Topo() []string {
topo := make([]string, 0, len(g.Nodes))
marks := make(map[string]bool)
var visit func(n string)
visit = func(n string) {
if marks[n] {
return
}
for _, to := range g.Edges(n) {
visit(to)
}
marks[n] = true
topo = append(topo, n)
}
for _, root := range g.Nodes {
visit(root)
}
for i, j := 0, len(topo)-1; i < j; i, j = i+1, j-1 {
topo[i], topo[j] = topo[j], topo[i]
}
return topo
}
// TransitiveReduction removes edges from g that are transitively
// reachable. g must be transitively closed.
func (g *Graph) TransitiveReduction() {
// For i -> j -> k, if i -> k exists, delete it.
for _, i := range g.Nodes {
for _, j := range g.Nodes {
if g.HasEdge(i, j) {
for _, k := range g.Nodes {
if g.HasEdge(j, k) {
g.DelEdge(i, k)
}
}
}
}
}
}