@@ -2,6 +2,35 @@ package eu.sim642.adventofcodelib.graph
22
33object BronKerbosch {
44
5+ // unused
6+ def maximalCliques [A ](neighbors : Map [A , Set [A ]]): Iterator [Set [A ]] = {
7+ 8+ def bronKerbosch (r : Set [A ], p : Set [A ], x : Set [A ]): Iterator [Set [A ]] = {
9+ if (p.isEmpty) {
10+ if (x.isEmpty)
11+ Iterator .single(r)
12+ else
13+ Iterator .empty
14+ }
15+ else {
16+ // val u = p.headOption.getOrElse(x.head)
17+ val u = (p ++ x).maxBy(neighbors(_).size) // pivot on highest degree
18+ val vs = (p -- neighbors(u)).iterator
19+ Iterator .unfold((p, x))((p, x) => // foldLeftFlatMap
20+ vs.nextOption().map(v =>
21+ (bronKerbosch(r + v, p intersect neighbors(v), x intersect neighbors(v)), (p - v, x + v))
22+ )
23+ ).flatten
24+ }
25+ }
26+ 27+ bronKerbosch(Set .empty, neighbors.keySet, Set .empty)
28+ }
29+ 30+ // TODO: would this be slower than direct implementation below?
31+ /* def maximumClique[A](neighbors: Map[A, Set[A]]): Set[A] =
32+ maximalCliques(neighbors).maxBy(_.size)*/
33+ 534 // moved from 2018 day 23
635 def maximumClique [A ](neighbors : Map [A , Set [A ]]): Set [A ] = {
736 var best : Set [A ] = Set .empty
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