-
-
Save gengyu89/95da2c924d4447fa6c455517be8b7ad0 to your computer and use it in GitHub Desktop.
Tarjan's algorithm for Scala
This file contains hidden or bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
| package tarjan | |
| import scala.collection.mutable | |
| // See python version: https://github.com/bwesterb/py-tarjan | |
| /** | |
| * Tarjan's algorithm is an algorithm in graph theory for finding the strongly connected components of a directed graph. It runs in linear time, | |
| * matching the time bound for alternative methods including Kosaraju's algorithm and the path-based strong component algorithm. | |
| */ | |
| class TarjanRecursive { | |
| /** | |
| * The algorithm takes a directed graph as input, a | |
| * nd produces a partition of the graph's vertices into the graph's strongly connected components. | |
| * @param g the graph | |
| * @return the strongly connected components of g | |
| */ | |
| def apply(g: Map[Int, List[Int]]): mutable.Buffer[mutable.Buffer[Int]] = { | |
| val s = mutable.Buffer.empty[Int] | |
| val s_set = mutable.Set.empty[Int] | |
| val index = mutable.Map.empty[Int, Int] | |
| val lowlink = mutable.Map.empty[Int, Int] | |
| val ret = mutable.Buffer.empty[mutable.Buffer[Int]] | |
| def visit(v: Int): Unit = { | |
| index(v) = index.size | |
| lowlink(v) = index(v) | |
| s += v | |
| s_set += v | |
| for (w <- g(v)) { | |
| if (!index.contains(w)) { | |
| visit(w) | |
| lowlink(v) = math.min(lowlink(w), lowlink(v)) | |
| } else if (s_set(w)) { | |
| lowlink(v) = math.min(lowlink(v), index(w)) | |
| } | |
| } | |
| if (lowlink(v) == index(v)) { | |
| val scc = mutable.Buffer.empty[Int] | |
| var w = -1 | |
| while(v != w) { | |
| w = s.remove(s.size - 1) | |
| scc += w | |
| s_set -= w | |
| } | |
| ret += scc | |
| } | |
| } | |
| for (v <- g.keys) if (!index.contains(v)) visit(v) | |
| ret | |
| } | |
| } |
Sign up for free
to join this conversation on GitHub.
Already have an account?
Sign in to comment