TreeNode.js

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

  static parse(arr) {
    if (arr.length === 0)
      return null
    const root = new TreeNode(arr[0])
    const queue = [root]
    for (let i = 1; i < arr.length; i += 2) {
      const node = queue.shift()
      if (arr[i] !== null) {
        node.left = new TreeNode(arr[i])
        queue.push(node.left)
      }
      if (arr[i + 1] !== null) {
        node.right = new TreeNode(arr[i + 1])
        queue.push(node.right)
      }
    }
    return root
  }

  static toArray(treeNode) {
    const result = []
    if (!treeNode)
      return result

    const queue = [treeNode]

    while (queue.length > 0) {
      const node = queue.shift()
      if (node) {
        result.push(node.val)
        queue.push(node.left)
        queue.push(node.right)
      }
      else {
        result.push(null)
      }
    }

    while (result.length > 0 && result[result.length - 1] === null) result.pop()

    return result
  }
}