DFS.groovy

class DFS {
  def visitedNodeCounter = 0

  def visitor = {
    visitedNodeCounter++
  }

  def visit(node) {
    node.acceptVisitor visitor
    node.children.each { visit(it) }
  }
}

class Node {
  def children = []

  def addChild(node) {
    children << node
  }

  def acceptVisitor(visitor) {
    visitor()
  }
}

root = new Node()

100.times {
  root.addChild new Node()
}
root.children.each { child ->
  50.times { child.addChild new Node() }
}

dfs = new DFS()
dfs.visit(root)

result = dfs.visitedNodeCounter