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dfs.go
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dfs.go
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// Copyright 2023 Google LLC
//
// 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 "slices"
// DFSAll performs a depth first search of all nodes in g.
// If enter is non-nil, it is called on entry to a node.
// If exit is non-nil, it is called on exit from a node.
func DFSAll(g Graph, enter, exit func(Node)) {
var all []Node
g.PerNode(func(n Node) {
all = append(all, n)
})
dfs(g, all, enter, exit)
}
// PostOrder returns nodes in g in post-order.
func PostOrder(g Graph) []Node {
var result []Node
DFSAll(g, nil, func(n Node) {
result = append(result, n)
})
return result
}
// ReversePostOrder returns nodes in g in reverse-post-order.
func ReversePostOrder(g Graph) []Node {
result := PostOrder(g)
slices.Reverse(result)
return result
}
func dfs(g Graph, roots []Node, enter, exit func(Node)) {
// Stack holds nodes to traverse. If we need to call exit, we
// leave a negative marker at the appropriate place in the stack.
var stack []Node
visited := make([]bool, g.NodeLimit())
for _, r := range roots {
stack = append(stack, r)
for len(stack) > 0 {
n := stack[len(stack)-1]
stack = stack[:len(stack)-1]
if n < 0 {
exit(-n - 1)
continue
}
if visited[n] {
continue
}
visited[n] = true
if exit != nil {
stack = append(stack, -n-1) // Exit marker
}
if enter != nil {
enter(n)
}
g.PerOutEdge(n, func(e Edge) {
stack = append(stack, e.Dst)
})
}
}
}