// Kruskal generates a minimum spanning tree of g by greedy tree coalesence, placing
// the result in the destination. The destination is not cleared first.
func Kruskal(dst graph.MutableUndirected, g EdgeListerGraph) {
var weight graph.WeightFunc
if g, ok := g.(graph.Weighter); ok {
weight = g.Weight
} else {
weight = graph.UniformCost
}
edgeList := g.Edges()
edges := make([]concrete.WeightedEdge, 0, len(edgeList))
for _, edge := range edgeList {
edges = append(edges, concrete.WeightedEdge{Edge: edge, Cost: weight(edge)})
}
sort.Sort(byWeight(edges))
ds := newDisjointSet()
for _, node := range g.Nodes() {
ds.makeSet(node.ID())
}
for _, edge := range edges {
// The disjoint set doesn't really care for which is head and which is tail so this
// should work fine without checking both ways
if s1, s2 := ds.find(edge.Edge.From().ID()), ds.find(edge.Edge.To().ID()); s1 != s2 {
ds.union(s1, s2)
dst.SetEdge(edge.Edge, edge.Cost)
}
}
}
// Kruskal generates a minimum spanning tree of g by greedy tree coalesence, placing
// the result in the destination. The destination is not cleared first.
func Kruskal(dst graph.MutableUndirected, g EdgeListerGraph) {
var weight Weighting
if wg, ok := g.(graph.Weighter); ok {
weight = wg.Weight
} else {
weight = UniformCost(g)
}
edgeList := g.Edges()
edges := make([]concrete.Edge, 0, len(edgeList))
for _, e := range edgeList {
u := e.From()
v := e.To()
w, ok := weight(u, v)
if !ok {
panic("kruskal: unexpected invalid weight")
}
edges = append(edges, concrete.Edge{F: u, T: v, W: w})
}
sort.Sort(byWeight(edges))
ds := newDisjointSet()
for _, node := range g.Nodes() {
ds.makeSet(node.ID())
}
for _, e := range edges {
// The disjoint set doesn't really care for which is head and which is tail so this
// should work fine without checking both ways
if s1, s2 := ds.find(e.From().ID()), ds.find(e.To().ID()); s1 != s2 {
ds.union(s1, s2)
dst.SetEdge(e)
}
}
}
// Prim generates a minimum spanning tree of g by greedy tree extension, placing
// the result in the destination. The destination is not cleared first.
func Prim(dst graph.MutableUndirected, g EdgeListerGraph) {
var weight Weighting
if wg, ok := g.(graph.Weighter); ok {
weight = wg.Weight
} else {
weight = UniformCost(g)
}
nlist := g.Nodes()
if nlist == nil || len(nlist) == 0 {
return
}
dst.AddNode(nlist[0])
remain := make(internal.IntSet)
for _, node := range nlist[1:] {
remain.Add(node.ID())
}
edgeList := g.Edges()
for remain.Count() != 0 {
var edges []concrete.Edge
for _, e := range edgeList {
u := e.From()
v := e.To()
if (dst.Has(u) && remain.Has(v.ID())) || (dst.Has(v) && remain.Has(u.ID())) {
w, ok := weight(u, v)
if !ok {
panic("prim: unexpected invalid weight")
}
edges = append(edges, concrete.Edge{F: u, T: v, W: w})
}
}
sort.Sort(byWeight(edges))
min := edges[0]
dst.SetEdge(min)
remain.Remove(min.From().ID())
}
}
// Prim generates a minimum spanning tree of g by greedy tree extension, placing
// the result in the destination. The destination is not cleared first.
func Prim(dst graph.MutableUndirected, g EdgeListerGraph) {
var weight graph.WeightFunc
if g, ok := g.(graph.Weighter); ok {
weight = g.Weight
} else {
weight = graph.UniformCost
}
nlist := g.Nodes()
if nlist == nil || len(nlist) == 0 {
return
}
dst.AddNode(nlist[0])
remainingNodes := make(internal.IntSet)
for _, node := range nlist[1:] {
remainingNodes.Add(node.ID())
}
edgeList := g.Edges()
for remainingNodes.Count() != 0 {
var edges []concrete.WeightedEdge
for _, edge := range edgeList {
if (dst.Has(edge.From()) && remainingNodes.Has(edge.To().ID())) ||
(dst.Has(edge.To()) && remainingNodes.Has(edge.From().ID())) {
edges = append(edges, concrete.WeightedEdge{Edge: edge, Cost: weight(edge)})
}
}
sort.Sort(byWeight(edges))
myEdge := edges[0]
dst.SetEdge(myEdge.Edge, myEdge.Cost)
remainingNodes.Remove(myEdge.Edge.From().ID())
}
}