需要Scala Graph Cycle Detection Algo 'return'吗？

Question

我在 Scala 中为 DAG 实现了一个小循环检测算法。'return' 困扰着我 - 我想要一个没有 return 的版本...可能吗？

  def isCyclic() : Boolean = {
    lock.readLock().lock()
    try {
      nodes.foreach(node => node.marker = 1)
      nodes.foreach(node => {if (1 == node.marker && visit(node)) return true})
    } finally {
      lock.readLock().unlock()
    }
    false
  }

  private def visit(node: MyNode): Boolean = {
    node.marker = 3

    val nodeId = node.id
    val children = vertexMap.getChildren(nodeId).toList.map(nodeId => id2nodeMap(nodeId))
    children.foreach(child => {
      if (3 == child.marker || (1 == child.marker && visit(child))) return true
    })

    node.marker = 2

    false
  }

Answer 1

是的，使用 '.find' 而不是 'foreach' + 'return':

http://www.scala-lang.org/api/current/index.html#scala.collection.immutable.Seq

def isCyclic() : Boolean = {
  def visit(node: MyNode): Boolean = {
      node.marker = 3

      val nodeId = node.id
      val children = vertexMap.getChildren(nodeId).toList.map(nodeId => id2nodeMap(nodeId))
      val found = children.exists(child => (3 == child.marker || (1 == child.marker && visit(child))))

      node.marker = 2

      found
  }

  lock.readLock().lock()
  try {
    nodes.foreach(node => node.marker = 1)
    nodes.exists(node => node.marker && visit(node))
  } finally {
    lock.readLock().unlock()
  }
}