// 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())
}
}