maxAncestorDiff.scala

def maxAncestorDiff(root: TreeNode): Int = {
  def visit(node: TreeNode, min: Int, max: Int): Int = {
    if (node == null) return 0

    val diff = math.max(math.abs(node.value - max), math.abs(node.value - min))
    val newMin = math.min(node.value, min)
    val newMax = math.max(node.value, max)

    math.max(math.max(diff, visit(node.left, newMin, newMax)), visit(node.right, newMin, newMax))
  }

  visit(root, root.value, root.value)
}