forked from LaconicNetwork/kompose
56 lines
1.3 KiB
Go
56 lines
1.3 KiB
Go
// Copyright ©2015 The gonum Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style
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// license that can be found in the LICENSE file.
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package path
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import "github.com/gonum/graph"
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// FloydWarshall returns a shortest-path tree for the graph g or false indicating
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// that a negative cycle exists in the graph. If the graph does not implement
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// graph.Weighter, graph.UniformCost is used.
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//
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// The time complexity of FloydWarshall is O(|V|^3).
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func FloydWarshall(g graph.Graph) (paths AllShortest, ok bool) {
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var weight graph.WeightFunc
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if g, ok := g.(graph.Weighter); ok {
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weight = g.Weight
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} else {
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weight = graph.UniformCost
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}
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nodes := g.Nodes()
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paths = newAllShortest(nodes, true)
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for i, u := range nodes {
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paths.dist.Set(i, i, 0)
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for _, v := range g.From(u) {
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j := paths.indexOf[v.ID()]
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paths.set(i, j, weight(g.Edge(u, v)), j)
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}
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}
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for k := range nodes {
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for i := range nodes {
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for j := range nodes {
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ij := paths.dist.At(i, j)
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joint := paths.dist.At(i, k) + paths.dist.At(k, j)
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if ij > joint {
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paths.set(i, j, joint, paths.at(i, k)...)
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} else if ij-joint == 0 {
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paths.add(i, j, paths.at(i, k)...)
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}
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}
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}
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}
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ok = true
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for i := range nodes {
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if paths.dist.At(i, i) < 0 {
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ok = false
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break
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}
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}
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return paths, ok
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}
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