二叉搜索树 BST

class TreeNode {
  val: number
  left: TreeNode | null
  right: TreeNode | null
  constructor(val?: number, left?: TreeNode | null, right?: TreeNode | null) {
    this.val = (val == undefined ? 0 : val)
    this.left = (left == undefined ? null : left)
    this.right = (right == undefined ? null : right)
  }
}

const insertIntoBST = (root: TreeNode | null, val: number): TreeNode | null => {
  if (root == null) return new TreeNode(val)
 
  if (val < root.val)

const deleteNode = (root: TreeNode | null, key: number): TreeNode | null => {
  if (root == null) return root
 
  if (root.val == key) {
    if