二叉树

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 preorderTraversal = (root: TreeNode | null): number[] => {
  if (root == null) return []
  return [root.val, ...preorderTraversal(root.left), ...preorderTraversal

const preorderTraversal = (root: TreeNode | null): number[] => {
  const ans: number[] = []
 
  const stack: TreeNode[] = [root]
  while

const inorderTraversal = (root: TreeNode | null): number[] => {
  if (root == null) return []
  return [...inorderTraversal(root.left), root.val, ...inorderTraversal(

const inorderTraversal = (root: TreeNode | null): number[] => {
  const ans: number[] = []
 
  const stack: TreeNode[] = []
  let cur

const postorderTraversal = (root: TreeNode | null): number[] => {
  if (root == null) return []
  return [...postorderTraversal(root.left), ...postorderTraversal(

const postorderTraversal = (root: TreeNode | null): number[] => {
  const ans: number[] = []
 
  const stack: TreeNode[] = [root]
  while

const levelOrder = (root: TreeNode | null): number[][] => {
  const ans: number[][] = []
 
  const dfs = (node: TreeNode |

const levelOrder = (root: TreeNode | null): number[][] => {
  if (root == null) return []
 
  const ans: number[][] =

const buildTree = (preorder: number[], inorder: number[]): TreeNode | null => {
  if (preorder.length == 0) return null
 
  const root_val = preorder[0]

const buildTree = (inorder: number[], postorder: number[]): TreeNode | null => {
  if (postorder.length == 0) return null
 
  const root_val = postorder.at(-

const buildTree = (preorder: number[], postorder: number[]): TreeNode | null => {
  if(preorder.length == 0) return null
 
  const [root_val, sub_root_val] =