68 lines
1.9 KiB
Go
68 lines
1.9 KiB
Go
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// Copyright (c) 2016 Bitfury Group Limited
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// Distributed under the MIT software license, see the accompanying
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// file LICENSE or http://www.opensource.org/licenses/mit-license.php
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package graph
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import "math"
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// KShortestPaths finds k shortest paths
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// Note: this implementation finds k path not necessary shortest
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// It tries to make that distinct and shortest at the same time
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func KShortestPaths(g *Graph, source, target Vertex, k int) ([][]Vertex, error) {
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ksp := make([][]Vertex, 0, k)
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DRY := make(map[string]bool)
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actualNodeWeight := make(map[Vertex]float64, g.GetVertexCount())
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for _, id := range g.GetVertexes() {
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actualNodeWeight[id] = 1
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}
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const UselessIterations = 200
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for cnt := 0; len(ksp) < k && cnt < UselessIterations; cnt++ {
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if err := modifyEdgeWeight(g, actualNodeWeight); err != nil {
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return nil, err
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}
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path, err := DijkstraPath(g, source, target)
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if err != nil {
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return nil, err
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}
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for _, v := range path {
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actualNodeWeight[v]++
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}
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key := ""
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for _, v := range path {
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key += v.String()
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}
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if !DRY[key] {
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DRY[key] = true
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ksp = append(ksp, path)
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cnt = 0
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}
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}
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return ksp, nil
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}
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func modifyEdgeWeight(g *Graph, actualNodeWeight map[Vertex]float64) error {
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for _, v1 := range g.GetVertexes() {
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targets, err := g.GetNeighbors(v1)
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if err != nil {
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return err
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}
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for v2, multiedges := range targets {
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for ID := range multiedges {
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wgt := calcEdgeWeight(actualNodeWeight, v1, v2)
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g.ReplaceUndirectedEdge(v1, v2, ID, &ChannelInfo{Wgt: wgt})
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}
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}
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}
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return nil
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}
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// Calculate new edge weight based on vertex weights.
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// It uses empirical formulae
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// weight(i, j) = (weight(i) + weight(j)) ^ 6
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// Number 6 was choosen because it gives best results in several simulations
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func calcEdgeWeight(actualNodeWeight map[Vertex]float64, v1, v2 Vertex) float64 {
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const ExperiementalNumber = 6.0
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wgt := math.Pow(actualNodeWeight[v1]+actualNodeWeight[v2], ExperiementalNumber)
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return wgt
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}
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