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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,49 @@ | ||
| package scalan.util | ||
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| import scalan.{DFunc, DFuncAdapter} | ||
| import debox.{Buffer => DBuffer} | ||
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| import scala.reflect.ClassTag | ||
| import spire.syntax.all.cfor | ||
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| object GraphUtilEx { | ||
| /** | ||
| * Returns the strongly connected components | ||
| * of the graph rooted at the startNodes argument, | ||
| * whose edges are given by the function argument `succ`. | ||
| * | ||
| * @see Tarjan, Robert E.. “Depth-First Search and Linear Graph Algorithms.” SIAM J. Comput. 1 (1972): 146-160. | ||
| */ | ||
| def stronglyConnectedComponents[@specialized(Int) T: ClassTag](startNodes: DBuffer[T], succ: DFunc[T, DBuffer[T]]): DBuffer[DBuffer[T]] = { | ||
| val tarjan = new Tarjan[T](succ) | ||
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| // top level loop of the algorithm | ||
| cfor(0)(_ < startNodes.length, _ + 1) { i => | ||
| val node = startNodes(i) | ||
| tarjan.visit(node) | ||
| } | ||
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| tarjan.res | ||
| } | ||
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| def stronglyConnectedComponents[@specialized(Int) T: ClassTag](start: Array[T])(succ: T => DBuffer[T]): DBuffer[DBuffer[T]] = { | ||
| stronglyConnectedComponents(DBuffer.fromArray(start), new DFuncAdapter(succ)) | ||
| } | ||
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| def buildScheduleForResult(startNodes: DBuffer[Int], neighbours: DFunc[Int, DBuffer[Int]]): DBuffer[Int] = { | ||
| val components = GraphUtilEx.stronglyConnectedComponents(startNodes, neighbours) | ||
| val nComponents = components.length | ||
| if (nComponents == 1) { | ||
| components(0) | ||
| } else { | ||
| val res = DBuffer.ofSize[Int](components(0).length) | ||
| cfor(0)(_ < nComponents, _ + 1) { i => | ||
| res ++= components(i) | ||
| } | ||
| res | ||
| } | ||
| } | ||
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| val initTarjan = new Tarjan[Int](new DFuncAdapter((i: Int) => DBuffer(i))) | ||
| } | ||
|
|
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,52 @@ | ||
| package scalan.util | ||
|
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| import scala.reflect.ClassTag | ||
| import spire.syntax.all.cfor | ||
| import scalan.DFunc | ||
| import debox.{Buffer => DBuffer, Map => DMap} | ||
|
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| /** Implementation of the SCC part of Tarjan algorithm. */ | ||
| final class Tarjan[@specialized(Int) T: ClassTag](private var getNeighbours: DFunc[T, DBuffer[T]]) { | ||
| private var id = 0 | ||
| private var stack: DBuffer[T] = DBuffer.empty | ||
| private val mark = DMap.ofSize[T,Int](127) | ||
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| val res: DBuffer[DBuffer[T]] = DBuffer.empty | ||
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| /** Explore the next graph node. Returns quickly if the node is already marked. | ||
| * @return mark assigned to `node` */ | ||
| def visit(node: T): Int = { | ||
| val n = mark.getOrElse(node, -1) | ||
| if (n >= 0) return n | ||
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| id += 1 | ||
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| mark.update(node, id) | ||
| stack += node | ||
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| var min: Int = id | ||
| val neighbours = getNeighbours(node) | ||
| cfor(0)(_ < neighbours.length, _ + 1) { i => | ||
| val child = neighbours(i) | ||
| val m = visit(child) | ||
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| if (m < min) | ||
| min = m | ||
| } | ||
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| if (min == mark(node)) { | ||
| val scc = DBuffer.empty[T] | ||
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| var loop: Boolean = true | ||
| do { | ||
| val element = stack.pop | ||
| scc += element | ||
| mark.update(element, Integer.MAX_VALUE) | ||
| loop = element != node | ||
| } while (loop) | ||
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| res += scc | ||
| } | ||
| min | ||
| } | ||
| } |
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