58 lines
1.9 KiB
Scala
58 lines
1.9 KiB
Scala
import scala.collection.mutable
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class Dijkstra[Key] {
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type PathInfo = (Double, List[Key])
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type Path = List[Key]
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type MinHeap[PathInfo] = mutable.PriorityQueue[PathInfo]
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final def dijkstra(weightedGraph: Map[Key, List[(Double, Key)]],
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start: Key,
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dest: Key)(implicit ord: Ordering[PathInfo]): PathInfo =
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dijkstraHelper(weightedGraph, mutable.PriorityQueue((0.0, List(start))), dest)
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@annotation.tailrec
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private final def dijkstraHelper(weightedGraph: Map[Key, List[(Double, Key)]],
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fringe: MinHeap[PathInfo],
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dest: Key,
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visited: Set[Key] = Set.empty[Key])(implicit ord: Ordering[PathInfo]): PathInfo = {
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def updateFringe(frng: MinHeap[PathInfo], currentDist: Double, currentPath: Path): MinHeap[PathInfo] =
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(currentPath : @unchecked) match {
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case keys @ key :: _ =>
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weightedGraph(key)
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.withFilter { case (_, k) => !visited.contains(k) }
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.map { case (d, k) => (currentDist + d, k :: keys) } // updated PathInfo's
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.foreach { p => frng.enqueue(p) }
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frng
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}
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if (fringe.isEmpty)
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(0, Nil)
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else {
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(fringe.dequeue() : @unchecked) match {
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case (dist, path @ `dest` :: _) =>
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(dist, path.reverse)
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case (dist, path @ key :: _) =>
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dijkstraHelper(weightedGraph, updateFringe(fringe, dist, path), dest, visited + key)
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}
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}
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}
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def main(x: Array[String]): Unit = {
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val weightedGraph = Map(
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"a" -> List((7.0, "b"), (9.0, "c"), (14.0, "f")),
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"b" -> List((10.0, "c"), (15.0, "d")),
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"c" -> List((11.0, "d"), (2.0, "f")),
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"d" -> List((6.0, "e")),
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"e" -> List((9.0, "f")),
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"f" -> Nil
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)
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val res = dijkstra[String](weightedGraph, "a", "e")
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println(res)
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}
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}
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