diff options
Diffstat (limited to 'core/src/main/scala/forge/Tarjans.scala')
-rw-r--r-- | core/src/main/scala/forge/Tarjans.scala | 50 |
1 files changed, 50 insertions, 0 deletions
diff --git a/core/src/main/scala/forge/Tarjans.scala b/core/src/main/scala/forge/Tarjans.scala new file mode 100644 index 00000000..9831fe7f --- /dev/null +++ b/core/src/main/scala/forge/Tarjans.scala @@ -0,0 +1,50 @@ +package forge + +import collection.mutable +// Adapted from +// https://github.com/indy256/codelibrary/blob/c52247216258e84aac442a23273b7d8306ef757b/java/src/SCCTarjan.java +object Tarjans { + def apply(graph0: Seq[Seq[Int]]): Seq[Seq[Int]] = { + val graph = graph0.map(_.toArray).toArray + val n = graph.length + val visited = new Array[Boolean](n) + val stack = mutable.ArrayBuffer.empty[Integer] + var time = 0 + val lowlink = new Array[Int](n) + val components = mutable.ArrayBuffer.empty[Seq[Int]] + + + for (u <- 0 until n) { + if (!visited(u)) dfs(u) + } + + def dfs(u: Int): Unit = { + lowlink(u) = time + time += 1 + visited(u) = true + stack.append(u) + var isComponentRoot = true + for (v <- graph(u)) { + if (!visited(v)) dfs(v) + if (lowlink(u) > lowlink(v)) { + lowlink(u) = lowlink(v) + isComponentRoot = false + } + } + if (isComponentRoot) { + val component = mutable.Buffer.empty[Int] + + var done = false + while (!done) { + val x = stack.last + stack.remove(stack.length - 1) + component.append(x) + lowlink(x) = Integer.MAX_VALUE + if (x == u) done = true + } + components.append(component) + } + } + components + } +}
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