77 lines
1.7 KiB
Go
77 lines
1.7 KiB
Go
|
package dag
|
||
|
|
|
||
|
|
// StronglyConnected returns the list of strongly connected components
|
||
|
|
// within the Graph g. This information is primarily used by this package
|
||
|
|
// for cycle detection, but strongly connected components have widespread
|
||
|
|
// use.
|
||
|
|
func StronglyConnected(g *Graph) [][]Vertex {
|
||
|
|
vs := g.Vertices()
|
||
|
|
data := tarjanData{
|
||
|
|
index: make(map[interface{}]int),
|
||
|
|
stack: make([]*tarjanVertex, 0, len(vs)),
|
||
|
|
vertices: make([]*tarjanVertex, 0, len(vs)),
|
||
|
|
}
|
||
|
|
|
||
|
|
for _, v := range vs {
|
||
|
|
if _, ok := data.index[v]; !ok {
|
||
|
|
strongConnect(g, v, &data)
|
||
|
|
}
|
||
|
|
}
|
||
|
|
|
||
|
|
return data.result
|
||
|
|
}
|
||
|
|
|
||
|
|
type tarjanData struct {
|
||
|
|
index map[interface{}]int
|
||
|
|
result [][]Vertex
|
||
|
|
stack []*tarjanVertex
|
||
|
|
vertices []*tarjanVertex
|
||
|
|
}
|
||
|
|
|
||
|
|
type tarjanVertex struct {
|
||
|
|
V Vertex
|
||
|
|
Lowlink int
|
||
|
|
Index int
|
||
|
|
Stack bool
|
||
|
|
}
|
||
|
|
|
||
|
|
func strongConnect(g *Graph, v Vertex, data *tarjanData) *tarjanVertex {
|
||
|
|
index := len(data.index)
|
||
|
|
data.index[v] = index
|
||
|
|
tv := &tarjanVertex{V: v, Lowlink: index, Index: index, Stack: true}
|
||
|
|
data.stack = append(data.stack, tv)
|
||
|
|
data.vertices = append(data.vertices, tv)
|
||
|
|
|
||
|
|
for _, raw := range g.downEdges[v].List() {
|
||
|
|
target := raw.(Vertex)
|
||
|
|
|
||
|
|
if idx, ok := data.index[target]; !ok {
|
||
|
|
if tv2 := strongConnect(g, target, data); tv2.Lowlink < tv.Lowlink {
|
||
|
|
tv.Lowlink = tv2.Lowlink
|
||
|
|
}
|
||
|
|
} else if data.vertices[idx].Stack {
|
||
|
|
if idx < tv.Lowlink {
|
||
|
|
tv.Lowlink = idx
|
||
|
|
}
|
||
|
|
}
|
||
|
|
}
|
||
|
|
|
||
|
|
if tv.Lowlink == index {
|
||
|
|
vs := make([]Vertex, 0, 2)
|
||
|
|
for i := len(data.stack) - 1; ; i-- {
|
||
|
|
v := data.stack[i]
|
||
|
|
data.stack[i] = nil
|
||
|
|
data.stack = data.stack[:i]
|
||
|
|
data.vertices[data.index[v]].Stack = false
|
||
|
|
vs = append(vs, v.V)
|
||
|
|
if data.index[v] == i {
|
||
|
|
break
|
||
|
|
}
|
||
|
|
}
|
||
|
|
|
||
|
|
data.result = append(data.result, vs)
|
||
|
|
}
|
||
|
|
|
||
|
|
return tv
|
||
|
|
}
|