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