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95 lines
2.2 KiB
95 lines
2.2 KiB
package txn
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import (
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"gopkg.in/mgo.v2/bson"
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"sort"
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)
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func tarjanSort(successors map[bson.ObjectId][]bson.ObjectId) [][]bson.ObjectId {
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// http://en.wikipedia.org/wiki/Tarjan%27s_strongly_connected_components_algorithm
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data := &tarjanData{
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successors: successors,
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nodes: make([]tarjanNode, 0, len(successors)),
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index: make(map[bson.ObjectId]int, len(successors)),
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}
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for id := range successors {
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id := bson.ObjectId(string(id))
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if _, seen := data.index[id]; !seen {
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data.strongConnect(id)
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}
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}
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// Sort connected components to stabilize the algorithm.
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for _, ids := range data.output {
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if len(ids) > 1 {
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sort.Sort(idList(ids))
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}
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}
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return data.output
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}
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type tarjanData struct {
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successors map[bson.ObjectId][]bson.ObjectId
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output [][]bson.ObjectId
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nodes []tarjanNode
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stack []bson.ObjectId
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index map[bson.ObjectId]int
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}
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type tarjanNode struct {
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lowlink int
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stacked bool
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}
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type idList []bson.ObjectId
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func (l idList) Len() int { return len(l) }
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func (l idList) Swap(i, j int) { l[i], l[j] = l[j], l[i] }
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func (l idList) Less(i, j int) bool { return l[i] < l[j] }
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func (data *tarjanData) strongConnect(id bson.ObjectId) *tarjanNode {
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index := len(data.nodes)
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data.index[id] = index
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data.stack = append(data.stack, id)
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data.nodes = append(data.nodes, tarjanNode{index, true})
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node := &data.nodes[index]
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for _, succid := range data.successors[id] {
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succindex, seen := data.index[succid]
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if !seen {
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succnode := data.strongConnect(succid)
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if succnode.lowlink < node.lowlink {
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node.lowlink = succnode.lowlink
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}
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} else if data.nodes[succindex].stacked {
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// Part of the current strongly-connected component.
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if succindex < node.lowlink {
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node.lowlink = succindex
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}
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}
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}
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if node.lowlink == index {
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// Root node; pop stack and output new
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// strongly-connected component.
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var scc []bson.ObjectId
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i := len(data.stack) - 1
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for {
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stackid := data.stack[i]
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stackindex := data.index[stackid]
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data.nodes[stackindex].stacked = false
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scc = append(scc, stackid)
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if stackindex == index {
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break
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}
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i--
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}
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data.stack = data.stack[:i]
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data.output = append(data.output, scc)
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}
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return node
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}
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