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