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// Copyright ©2020 The Gonum Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
package rdf
// djSet implements a disjoint set finder using the union-find algorithm.
type djSet map[string]*dsNode
// add adds e to the collection of sets held by the disjoint set.
func (s djSet) add(e string) {
if _, ok := s[e]; ok {
return
}
s[e] = &dsNode{}
}
// union joins two sets a and b within the collection of sets held by
// the disjoint set.
func (djSet) union(a, b *dsNode) {
ra := find(a)
rb := find(b)
if ra == rb {
return
}
if ra.rank < rb.rank {
ra.parent = rb
return
}
rb.parent = ra
if ra.rank == rb.rank {
ra.rank++
}
}
// find returns the root of the set containing e.
func (s djSet) find(e string) *dsNode {
n, ok := s[e]
if !ok {
return nil
}
return find(n)
}
// find returns the root of the set containing the set node, n.
func find(n *dsNode) *dsNode {
for ; n.parent != nil; n = n.parent {
}
return n
}
// dsNode is a disjoint set element.
type dsNode struct {
parent *dsNode
rank int
}
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