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Topological sorting: simple implementation in pure Scala
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| def tsort[A](edges: Traversable[(A, A)]): Iterable[A] = { | |
| @tailrec | |
| def tsort(toPreds: Map[A, Set[A]], done: Iterable[A]): Iterable[A] = { | |
| val (noPreds, hasPreds) = toPreds.partition { _._2.isEmpty } | |
| if (noPreds.isEmpty) { | |
| if (hasPreds.isEmpty) done else sys.error(hasPreds.toString) | |
| } else { | |
| val found = noPreds.map { _._1 } | |
| tsort(hasPreds.mapValues { _ -- found }, done ++ found) | |
| } | |
| } | |
| val toPred = edges.foldLeft(Map[A, Set[A]]()) { (acc, e) => | |
| acc + (e._1 -> acc.getOrElse(e._1, Set())) + (e._2 -> (acc.getOrElse(e._2, Set()) + e._1)) | |
| } | |
| tsort(toPred, Seq()) | |
| } | |
| println(tsort(Seq((1, 2), (2, 4), (3, 4), (3, 2), (1,3)))) |
this was useful, thanks. +1 to @infomarte's comment
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Would you mind to make this nice piece of code available under some permissive licence (like MIT or BSD) such that it can be used in open-source projects?