选项成员的Setters

Question

我正在尝试一个编码练习，任务是从二叉搜索树中删除一个节点。这是我目前所拥有的：

sealed trait Node {
  val label: Int
}
case class LeafNode(override val label: Int) extends Node
case class BranchNode(override val label: Int, var left: Option[Node], var right: Option[Node]) extends Node


def deleteFromBST(root: Option[Node], valueToDelete: Int): Option[Node] = {
   def doTheDelete(node: Option[Node], parent: Option[Node]): Option[Node] = (node, parent) match {
      // Handle other possibilities of (node, parent)
      ...
      // Case where the root needs replacement
      case (Some(BranchNode(label, left, right)), None) => {
         // Root replacement.
         // Get the replacement node and it's parent
         var (replacement, repParent) = getTheLeastInTheTree(right)
         // Mark the previous parent of the replacement node as not having this child anymore
         if (repParent.get.label > replacement.get.label) {
            repParent // <-- This is where I am stuck
         }
         ...
   }
   ...
}

为了保持代码简洁，我从上面的代码片段中删除了其他函数。现在，在“这就是我被卡住的地方”，我该如何将repParent的left或right节点设置为None呢？我以为在case class的BranchNode定义中将right和var声明为case classs会允许我对其进行更改吗？

Answer 1

您不能改变case class，因为case类背后的思想是保存不可变的数据。

但您可以做的是将数据复制到较新的数据中，并更改您想要的值。

  val leftNode = Option(LeafNode(2))
  val rightNode = Option(LeafNode(3))
  val root = BranchNode(1, leftNode, rightNode)

  //i'm deleting or Nonefying the right node in following example
  val newRoot = root.copy(right = None) //only overriding the right node
  assert(newRoot.label == 1)
  assert(newRoot.left == leftNode)
  assert(newRoot.right == None)