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author | Li Haoyi <haoyi.sg@gmail.com> | 2017-10-17 06:03:36 -0700 |
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committer | Li Haoyi <haoyi.sg@gmail.com> | 2017-10-17 06:11:28 -0700 |
commit | aa5eb186c044e0c00d512e0c009e9d519a753e0c (patch) | |
tree | c4d28c2132c303578b3038deac1b36752520b5ed /src/main/scala/hbt/Tarjans.scala | |
parent | def1d68ebacc38cc93f4de83f5ed08ee6014d806 (diff) | |
download | mill-aa5eb186c044e0c00d512e0c009e9d519a753e0c.tar.gz mill-aa5eb186c044e0c00d512e0c009e9d519a753e0c.tar.bz2 mill-aa5eb186c044e0c00d512e0c009e9d519a753e0c.zip |
Include Tarjan's algorithm, for doing a topological sort which elegantly handles cycles
Diffstat (limited to 'src/main/scala/hbt/Tarjans.scala')
-rw-r--r-- | src/main/scala/hbt/Tarjans.scala | 61 |
1 files changed, 61 insertions, 0 deletions
diff --git a/src/main/scala/hbt/Tarjans.scala b/src/main/scala/hbt/Tarjans.scala new file mode 100644 index 00000000..dc95b02f --- /dev/null +++ b/src/main/scala/hbt/Tarjans.scala @@ -0,0 +1,61 @@ +package hbt + +import collection.mutable +// Adapted from +// https://github.com/indy256/codelibrary/blob/c52247216258e84aac442a23273b7d8306ef757b/java/src/SCCTarjan.java +object Tarjans { + def main(args: Array[String]) = { + val components = Tarjans( + Vector( + Vector(1), + Vector(0), + Vector(0, 1) + ) + ) + println(components) + } + + 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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